View source for Perception

{{Short description|Interpretation of sensory information}}
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{{Other uses|Perception (disambiguation)}}
{{redirect|Percept|other uses|Percept (disambiguation)}}
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[[File:Multistability.svg|thumb|The [[Necker cube]] and [[Rubin vase]] can be perceived in more than one way.]]
[[File:Synthesizing_3D_Shapes_via_Modeling_Multi-View_Depth_Maps_and_Silhouettes_With_Deep_Generative_Networks.png|thumb|Humans are able to make a very good guess on the underlying 3D shape category/identity/geometry given a silhouette of that shape. [[Computer vision]] researchers have been able to build computational models for perception that exhibit a similar behavior and are capable of generating and [[3D reconstruction|reconstructing 3D shapes]] from single or multi-view depth maps or silhouettes.<ref name="3DVAE">{{Cite web |title=Your 8 Senses |url=https://sensoryhealth.org/basic/your-8-senses |access-date=2024-05-06 |website=sensoryhealth.org |language=en}}</ref>]]
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'''Perception''' ({{etymology|la|{{wikt-lang|la|perceptio}}|gathering, receiving}}) is the organization, identification, and interpretation of [[sense|sensory]] information, in order to represent and understand the presented information or environment.<ref>{{cite book |title=Psychology |url=https://archive.org/details/psychology0000scha |url-access=registration |last=Schacter |first=Daniel |publisher=Worth Publishers |year=2011 |isbn=978-1-4292-3719-2}}</ref> All perception involves signals that go through the [[nervous system]], which in turn result from physical or chemical stimulation of the [[Sensory nervous system|sensory system]].<ref name="Goldstein52">Goldstein (2009) pp. 5–7</ref> [[Visual system|Vision]] involves [[light]] striking the [[retina]] of the [[eye]]; [[Sense of smell|smell]] is mediated by [[Olfactory system#Peripheral|odor molecules]]; and [[hearing]] involves [[Sound wave|pressure waves]].

Perception is not only the passive receipt of these [[Signal processing|signals]], but it is also shaped by the recipient's [[Perceptual learning|learning]], [[memory]], [[Expectation (epistemic)|expectation]], and [[attention]].<ref name="mind_perception2">[[Richard Gregory|Gregory, Richard]]. "Perception" in Gregory, Zangwill (1987) pp.&nbsp;598–601.</ref><ref name="Bernstein20102">{{cite book|url=https://books.google.com/books?id=rd77N0KsLVkC&pg=PA123|title=Essentials of Psychology|last=Bernstein|first=Douglas A.|date=5 March 2010|publisher=Cengage Learning|isbn=978-0-495-90693-3|pages=123–124|access-date=25 March 2011|archive-url=https://web.archive.org/web/20170102091148/https://books.google.com/books?id=rd77N0KsLVkC&pg=PA123|archive-date=2 January 2017|url-status=live}}</ref> Sensory input is a process that transforms this low-level information to higher-level information (e.g., extracts shapes for [[cognitive neuroscience of visual object recognition|object recognition]]).<ref name="Bernstein20102" /> The following process connects a person's concepts and expectations (or [[knowledge]]) with restorative and selective mechanisms, such as [[attention]], that influence perception.

Perception depends on complex functions of the [[nervous system]], but subjectively seems mostly effortless because this processing happens outside [[Consciousness|conscious]] [[awareness]].<ref name="Goldstein52"/> Since the rise of [[experimental psychology]] in the 19th century, [[Perceptual psychology|psychology's understanding of perception]] has progressed by combining a variety of techniques.<ref name="mind_perception2" /> [[Psychophysics]] [[quantitatively]] describes the relationships between the physical qualities of the sensory input and perception.<ref>[[Gustav Fechner|Gustav Theodor Fechner]]. Elemente der Psychophysik. Leipzig 1860.</ref> [[Sensory neuroscience]] studies the neural mechanisms underlying perception. Perceptual systems can also be studied [[computation]]ally, in terms of the information they process. [[Philosophy of perception|Perceptual issues in philosophy]] include the extent to which sensory qualities such as [[sound]], smell or [[color]] exist in objective reality rather than in the mind of the perceiver.<ref name="mind_perception2" />

Although people traditionally viewed the senses as passive receptors, the study of [[illusion]]s and [[ambiguous image]]s has demonstrated that the [[brain]]'s perceptual systems actively and pre-consciously attempt to make sense of their input.<ref name="mind_perception2" /> There is still active debate about the extent to which perception is an active process of [[hypothesis]] testing, analogous to [[science]], or whether realistic sensory information is rich enough to make this process unnecessary.<ref name="mind_perception2" />

The [[perceptual system]]s of the brain enable individuals to see the world around them as stable, even though the sensory information is typically incomplete and rapidly varying. Human and other animal brains are structured in a [[Cognitive module|modular way]], with different areas processing different kinds of sensory information. Some of these modules take the form of [[Sensory Maps|sensory maps]], mapping some aspect of the world across part of the brain's surface. These different modules are interconnected and influence each other. For instance, [[taste]] is strongly influenced by smell.<ref name="DeVereCalvert2010_332">{{cite book|url=https://books.google.com/books?id=m6WOtX2QAtwC&pg=PA39|title=Navigating Smell and Taste Disorders|last1=DeVere|first1=Ronald|last2=Calvert|first2=Marjorie|date=31 August 2010|publisher=Demos Medical Publishing|isbn=978-1-932603-96-5|pages=33–37|access-date=26 March 2011|archive-url=https://web.archive.org/web/20111109163210/http://books.google.com/books?id=m6WOtX2QAtwC&pg=PA39|archive-date=9 November 2011|url-status=live}}</ref>

== Process and terminology ==<!-- linked from disambiguation: update or define {{Anchor|Process and terminology}} if changed -->
The process of perception begins with an object in the real world, known as the ''[[distal]] stimulus'' or ''distal object''.<ref name="Goldstein52">Goldstein (2009) pp. 5–7</ref> By means of light, sound, or another physical process, the object stimulates the body's sensory organs. These sensory organs transform the input energy into neural activity—a process called ''[[Transduction (physiology)|transduction]]''.<ref name="Goldstein52" /><ref name="pomerantz">Pomerantz, James R. (2003): "Perception: Overview". In: Lynn Nadel (Ed.), ''Encyclopedia of Cognitive Science'', Vol.&nbsp;3, London: Nature Publishing Group, pp.&nbsp;527–537.</ref> This raw pattern of neural activity is called the ''proximal stimulus''.<ref name="Goldstein52" /> These neural signals are then transmitted to the brain and processed.<ref name="Goldstein52" /> The resulting mental re-creation of the distal stimulus is the ''percept''.

To explain the process of perception, an example could be an ordinary shoe. The shoe itself is the distal stimulus. When light from the shoe enters a person's eye and stimulates the retina, that stimulation is the proximal stimulus.<ref>{{cite web|url=http://www.learner.org/discoveringpsychology/07/e07glossary.html|title=Sensation and Perception|archive-url=https://web.archive.org/web/20110510081956/http://www.learner.org/discoveringpsychology/07/e07glossary.html|archive-date=10 May 2011|url-status=dead|access-date=24 March 2011}}</ref> The image of the shoe reconstructed by the brain of the person is the percept. Another example could be a ringing telephone. The ringing of the phone is the distal stimulus. The sound stimulating a person's auditory receptors is the proximal stimulus. The brain's interpretation of this as the "ringing of a telephone" is the percept.

The different kinds of sensation (such as warmth, sound, and taste) are called ''[[Stimulus modality|sensory modalities]]'' or ''stimulus modalities''.<ref name="pomerantz" /><ref name="WillisCoggeshall2004">{{cite book|url=https://books.google.com/books?id=uqnKCewO2voC&pg=PA1|title=Sensory Mechanisms of the Spinal Cord: Primary afferent neurons and the spinal dorsal horn|last1=Willis|first1=William D.|last2=Coggeshall|first2=Richard E.|date=31 January 2004|publisher=Springer|isbn=978-0-306-48033-1|page=1|access-date=25 March 2011|archive-url=https://web.archive.org/web/20111109162356/http://books.google.com/books?id=uqnKCewO2voC&pg=PA1|archive-date=9 November 2011|url-status=live}}</ref>

=== Bruner's model of the perceptual process ===
{{See also|Social identity theory}}
Psychologist [[Jerome Bruner]] developed a model of perception, in which people put "together the information contained in" a target and a situation to form "perceptions of ourselves and others based on social categories."<ref>{{Cite web|url=http://catalogue.pearsoned.ca/assets/hip/ca/hip_ca_pearsonhighered/samplechapter/013613436X.pdf|title=Perception, Attribution, and, Judgment of Others|website=Pearson Education|access-date=8 March 2020|archive-date=25 February 2021|archive-url=https://web.archive.org/web/20210225071326/http://catalogue.pearsoned.ca/assets/hip/ca/hip_ca_pearsonhighered/samplechapter/013613436X.pdf|url-status=dead}}</ref><ref name="Alan">Alan S. & Gary J. (2011). Perception, Attribution, and Judgment of Others. Organizational Behaviour: Understanding and Managing Life at Work, Vol. 7.</ref> This model is composed of three states:

# When people encounter an unfamiliar target, they are very open to the informational [[sensory cue|cue]]s contained in the target and the situation surrounding it.
# The first stage does not give people enough information on which to base perceptions of the target, so they will actively seek out cues to resolve this ambiguity. Gradually, people collect some familiar cues that enable them to make a rough categorization of the target.
# The cues become less open and selective. People try to search for more cues that confirm the categorization of the target. They actively ignore and distort cues that violate their initial perceptions. Their perception becomes more selective and they finally paint a consistent picture of the target.

=== Saks and John's three components to perception ===
According to Alan Saks and Gary Johns, there are three components to perception:<ref>Sincero, Sarah Mae. 2013. "Perception." ''Explorable.'' Retrieved 8 March 2020 (https://explorable.com/perception).</ref>{{Better source needed|reason=The current source is insufficiently reliable ([[WP:NOTRS]]).|date=March 2024}}

# '''The Perceiver''': a person whose awareness is focused on the stimulus, and thus begins to perceive it. There are many factors that may influence the perceptions of the perceiver, while the three major ones include (1) [[Motivation|motivational state]], (2) [[emotional state]], and (3) [[experience]]. All of these factors, especially the first two, greatly contribute to how the person perceives a situation. Oftentimes, the perceiver may employ what is called a "perceptual defense", where the person will only see what they want to see.
# '''The Target''': the ''object'' of perception; something or someone who is being perceived. The amount of information gathered by the sensory organs of the perceiver affects the interpretation and understanding about the target.
# '''The Situation''': the ''environmental'' factors, timing, and degree of stimulation that affect the process of perception. These factors may render a single stimulus to be left as merely a stimulus, not a percept that is subject for brain interpretation.

==== Multistable perception ====
Stimuli are not necessarily translated into a percept and rarely does a single stimulus translate into a percept. An ambiguous stimulus may sometimes be transduced into one or more percepts, experienced randomly, one at a time, in a process termed ''[[multistable perception]]''. The same stimuli, or absence of them, may result in different percepts depending on subject's culture and previous experiences.<ref>{{Cite journal |last1=Smith |first1=Eliot R. |last2=Zárate |first2=Michael A. |date=1992 |title=Exemplar-based model of social judgment. |url=http://dx.doi.org/10.1037//0033-295x.99.1.3 |journal=Psychological Review |volume=99 |issue=1 |pages=3–21 |doi=10.1037/0033-295x.99.1.3 |issn=0033-295X|url-access=subscription }}</ref>

Ambiguous figures demonstrate that a single stimulus can result in more than one percept. For example, the [[Rubin vase]] can be interpreted either as a vase or as two faces. The percept can bind sensations from multiple senses into a whole. A picture of a talking person on a television screen, for example, is bound to the sound of speech from speakers to form a percept of a talking person.

== Types of perception ==

=== Vision ===
{{main|Visual perception}}
[[File:Cerebrum lobes.png|thumb|400px|Cerebrum lobes]]
In many ways, vision is the primary human sense. Light is taken in through each eye and focused in a way which sorts it on the retina according to direction of origin. A dense surface of photosensitive cells, including rods, cones, and [[intrinsically photosensitive retinal ganglion cells]] captures information about the intensity, color, and position of incoming light. Some processing of texture and movement occurs within the neurons on the retina before the information is sent to the brain. In total, about 15 differing types of information are then forwarded to the brain proper via the optic nerve.<ref>{{cite journal|last1=Gollisch|first1=Tim|last2=Meister|first2=Markus|date=28 January 2010|title=Eye Smarter than Scientists Believed: Neural Computations in Circuits of the Retina|journal=Neuron|volume=65|issue=2|pages=150–164|doi=10.1016/j.neuron.2009.12.009|pmc=3717333|pmid=20152123}}</ref>

The timing of perception of a visual event, at points along the visual circuit, have been measured. A sudden alteration of light at a spot in the environment first alters photoreceptor cells in the [[retina]], which send a signal to the [[retina bipolar cell]] layer which, in turn, can activate a retinal ganglion neuron cell. A retinal ganglion cell is a bridging neuron that connects visual retinal input to the visual processing centers within the central nervous system.<ref name="pmid34093409">{{cite journal |vauthors=Kim US, Mahroo OA, Mollon JD, Yu-Wai-Man P |title=Retinal Ganglion Cells-Diversity of Cell Types and Clinical Relevance |journal=Front Neurol |volume=12 |article-number=661938 |date=2021 |pmid=34093409 |pmc=8175861 |doi=10.3389/fneur.2021.661938 |doi-access=free }}</ref> Light-altered neuron activation occurs within about 5–20 milliseconds in a rabbit retinal ganglion,<ref name="pmid9144251">{{cite journal |vauthors=Berry MJ, Warland DK, Meister M |title=The structure and precision of retinal spike trains |journal=Proc Natl Acad Sci U S A |volume=94 |issue=10 |pages=5411–6 |date=May 1997 |pmid=9144251 |pmc=24692 |doi=10.1073/pnas.94.10.5411 |bibcode=1997PNAS...94.5411B |doi-access=free }}</ref> although in a mouse retinal ganglion cell the initial spike takes between 40 and 240 milliseconds before the initial activation.<ref name="pmid31641196">{{cite journal |vauthors=Tengölics ÁJ, Szarka G, Ganczer A, Szabó-Meleg E, Nyitrai M, Kovács-Öller T, Völgyi B |title=Response Latency Tuning by Retinal Circuits Modulates Signal Efficiency |journal=Sci Rep |volume=9 |issue=1 |article-number=15110 |date=October 2019 |pmid=31641196 |pmc=6806000 |doi=10.1038/s41598-019-51756-y |bibcode=2019NatSR...915110T}}</ref> The initial activation can be detected by an [[action potential]] spike, a sudden spike in neuron membrane electric voltage.

A perceptual visual event measured in humans was the presentation to individuals of an anomalous word. If these individuals are shown a sentence, presented as a sequence of single words on a computer screen, with a puzzling word out of place in the sequence, the perception of the puzzling word can register on an electroencephalogram (EEG). In an experiment, human readers wore an elastic cap with 64 embedded electrodes distributed over their scalp surface.<ref name="pmid23515395">{{cite journal |vauthors=Kim AE, Gilley PM |title=Neural mechanisms of rapid sensitivity to syntactic anomaly |journal=Front Psychol |volume=4 |pages=45 |date=2013 |pmid=23515395 |pmc=3600774 |doi=10.3389/fpsyg.2013.00045 |doi-access=free }}</ref> Within 230 milliseconds of encountering the anomalous word, the human readers generated an event-related electrical potential alteration of their EEG at the left occipital-temporal channel, over the left occipital lobe and temporal lobe.

=== Sound ===
[[File:Anatomy of the Human Ear en.svg|right|thumb|Anatomy of the human ear. (The length of the auditory canal is exaggerated in this image.){{Anatomy of the human ear - color legend}}]]
[[Hearing]] (or ''audition'') is the ability to perceive [[sound]] by detecting [[vibration]]s (i.e., ''sonic'' detection). Frequencies capable of being heard by humans are called [[Audio frequency|''audio'' or ''audible'' ''frequencies'']], the range of which is typically considered to be between 20&nbsp;[[Hertz|Hz]] and 20,000&nbsp;Hz.<ref>{{cite web
| url=https://hypertextbook.com/facts/2003/ChrisDAmbrose.shtml
| title=Frequency range of human hearing
| first1=Christoper
| last1=D'Ambrose
| year=2003
| first2=Rizwan
| last2=Choudhary
| website=The Physics Factbook
| editor-last=Elert
| editor-first=Glenn
| accessdate=2022-01-22
}}</ref> Frequencies higher than audio are referred to as [[Ultrasound|''ultrasonic'']], while frequencies below audio are referred to as [[Infrasound|''infrasonic'']].

The [[auditory system]] includes the [[Ear|outer ears]], which collect and filter sound waves; the [[Ear|middle ear]], which transforms the sound pressure ([[impedance matching]]); and the [[Ear|inner ear]], which produces neural signals in response to the sound. By the ascending [[auditory pathway]] these are led to the [[primary auditory cortex]] within the [[temporal lobe]] of the human brain, from where the auditory information then goes to the [[cerebral cortex]] for further processing.

Sound does not usually come from a single source: in real situations, sounds from multiple sources and directions are [[mwod:superimpose|superimposed]] as they arrive at the ears. Hearing involves the computationally complex task of separating out sources of interest, identifying them and often estimating their distance and direction.<ref name="eop_constancy" />

=== Touch ===
{{main|Haptic perception}}The process of recognizing objects through touch is known as ''haptic perception''. It involves a combination of [[somatosensory]] perception of patterns on the skin surface (e.g., edges, curvature, and texture) and [[proprioception]] of hand position and conformation. People can rapidly and accurately identify three-dimensional objects by touch.<ref>{{cite journal|last1=Klatzky|first1=R. L.|last2=Lederman|first2=S. J.|last3=Metzger|first3=V. A.|year=1985|title=Identifying objects by touch: An "expert system."|journal=Perception & Psychophysics|volume=37|issue=4|pages=299–302|doi=10.3758/BF03211351|pmid=4034346|doi-access=free}}</ref> This involves exploratory procedures, such as moving the fingers over the outer surface of the object or holding the entire object in the hand.<ref>{{cite journal|last1=Lederman|first1=S. J.|last2=Klatzky|first2=R. L.|year=1987|title=Hand movements: A window into haptic object recognition|journal=Cognitive Psychology|volume=19|issue=3|pages=342–368|doi=10.1016/0010-0285(87)90008-9|pmid=3608405|s2cid=3157751}}</ref> Haptic perception relies on the forces experienced during touch.<ref name="Robles-de-la-torre2001">{{Cite journal|last1=Robles-de-la-torre|first1=Gabriel|last2=Hayward|first2=Vincent|year=2001|title=Force can overcome object geometry in the perception of shape through active touch|journal=Nature|volume=412|issue=6845|pages=445–448|doi=10.1038/35086588|pmid=11473320|bibcode=2001Natur.412..445R|s2cid=4413295}}</ref>

Professor [[James J. Gibson|Gibson]] defined the haptic system as "the sensibility of the individual to the world adjacent to his body by use of his body."<ref>{{cite book|title=The senses considered as perceptual systems.|url=https://archive.org/details/sensesconsidered00jame|url-access=registration|last=Gibson|first=J.J.|publisher=Houghton Mifflin|year=1966|isbn=978-0-313-23961-8|location=Boston}}</ref> Gibson and others emphasized the close link between body movement and haptic perception, where the latter is ''active exploration''.

The concept of haptic perception is related to the concept of [[extended physiological proprioception]] according to which, when using a tool such as a stick, perceptual experience is transparently transferred to the end of the tool.

=== Taste ===
{{main|Taste}}Taste (formally known as ''gustation'') is the ability to perceive the [[Flavor (taste)|flavor]] of substances, including, but not limited to, [[food]]. Humans receive tastes through sensory organs concentrated on the upper surface of the [[tongue]], called ''[[taste bud]]s'' or ''gustatory calyculi''<u>.</u><ref>[https://books.google.com/books?id=dNhFLnc6NRkC&pg=PA201 Human biology (Page 201/464)] {{webarchive|url=https://web.archive.org/web/20170102150409/https://books.google.com/books?id=dNhFLnc6NRkC&lpg=PA201|date=2 January 2017}} Daniel D. Chiras. Jones & Bartlett Learning, 2005.</ref> The human tongue has 100 to 150 taste receptor cells on each of its roughly-ten thousand taste buds.<ref name="DeVereCalvert2010_39">{{cite book|url=https://books.google.com/books?id=m6WOtX2QAtwC&pg=PA39|title=Navigating Smell and Taste Disorders|last1=DeVere|first1=Ronald|last2=Calvert|first2=Marjorie|date=31 August 2010|publisher=Demos Medical Publishing|isbn=978-1-932603-96-5|pages=39–40|access-date=26 March 2011|archive-url=https://web.archive.org/web/20111109163210/http://books.google.com/books?id=m6WOtX2QAtwC&pg=PA39|archive-date=9 November 2011|url-status=live}}</ref>

Traditionally, there have been four primary tastes: [[sweetness]], [[Bitter (taste)#Bitter|bitterness]], [[sourness]], and [[saltiness]]. The recognition and awareness of [[umami]], which is considered the fifth primary taste, is a relatively recent development in [[Western cuisine]].<ref>{{cite news|url=http://www.trendcentral.com/life/umami-dearest/|title=Umami Dearest: The mysterious fifth taste has officially infiltrated the food scene|date=23 February 2010|url-status=dead|archive-url=https://web.archive.org/web/20110418051954/http://www.trendcentral.com/life/umami-dearest/|archive-date=18 April 2011|publisher=trendcentral.com|access-date=26 March 2011}}</ref><ref>{{cite news|url=http://www.foodchannel.com/articles/article/8-food-trend-for-2010-i-want-my-umami/|title=#8 Food Trend for 2010: I Want My Umami|date=6 December 2009|url-status=live|archive-url=https://web.archive.org/web/20110711015658/http://www.foodchannel.com/articles/article/8-food-trend-for-2010-i-want-my-umami/|archive-date=11 July 2011|publisher=foodchannel.com}}</ref> Other tastes can be mimicked by combining these basic tastes,<ref name="DeVereCalvert2010_39" /><ref name="SiegelAlbers2006">{{cite book|url=https://books.google.com/books?id=Af0IyHtGCMUC&pg=PA825|title=Basic neurochemistry: molecular, cellular, and medical aspects|last1=Siegel|first1=George J.|last2=Albers|first2=R. Wayne|publisher=Academic Press|year=2006|isbn=978-0-12-088397-4|page=825|access-date=26 March 2011|archive-url=https://web.archive.org/web/20111109162711/http://books.google.com/books?id=Af0IyHtGCMUC&pg=PA825|archive-date=9 November 2011|url-status=live}}</ref> all of which contribute only partially to the sensation and [[Flavor (taste)|flavor]] of food in the mouth. Other factors include [[Odor|smell]], which is detected by the [[olfactory epithelium]] of the nose;<ref name="DeVereCalvert2010_332" /> [[Texture (food)|texture]], which is detected through a variety of [[mechanoreceptor]]s, muscle nerves, etc.;<ref name="SiegelAlbers2006" /><ref>[https://books.google.com/books?id=aJBIbvClWfcC&pg=PA4 Food texture: measurement and perception (page 3–4/311)] {{webarchive|url=https://web.archive.org/web/20170102091018/https://books.google.com/books?id=aJBIbvClWfcC&lpg=PP1&pg=PA4|date=2 January 2017}} Andrew J. Rosenthal. Springer, 1999.</ref> and temperature, which is detected by [[thermoreceptor]]s.<ref name="SiegelAlbers2006" /> All basic tastes are classified as either ''[[Reward system|appetitive]]'' or ''[[Aversives|aversive]]'', depending upon whether the things they sense are harmful or beneficial.<ref name="aa">[http://www.scientificamerican.com/article.cfm?id=two-great-tastes-not-great-together Why do two great tastes sometimes not taste great together?] {{webarchive|url=https://web.archive.org/web/20111128175618/http://www.scientificamerican.com/article.cfm?id=two-great-tastes-not-great-together|date=28 November 2011}} scientificamerican.com. Dr. Tim Jacob, Cardiff University. 22 May 2009.</ref>

=== Smell ===
{{main|Olfaction|l1 = Olfaction}}
Smell is the process of absorbing molecules through [[Olfactory system|olfactory organs]], which are absorbed by humans through the [[nose]]. These molecules diffuse through a thick layer of [[mucus]]; come into contact with one of thousands of [[Cilium|cilia]] that are projected from sensory neurons; and are then absorbed into a receptor (one of 347 or so).<ref>{{Cite journal|title=Science is perception: what can our sense of smell tell us about ourselves and the world around us?|journal = Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences|volume = 368|issue = 1924|pages = 3491–3502|last=Brookes|first=Jennifer|date=13 August 2010|pmc = 2944383|pmid = 20603363|doi = 10.1098/rsta.2010.0117|bibcode = 2010RSPTA.368.3491B}}</ref> It is this process that causes humans to understand the concept of smell from a physical standpoint.

Smell is also a very interactive sense as scientists have begun to observe that olfaction comes into contact with the other sense in unexpected ways.<ref>{{Cite web|url=https://www.apa.org/monitor/2011/02/scents.aspx|title=Scents and sensibility|last=Weir|first=Kirsten|date=February 2011|website=American Psychological Association|access-date=11 December 2018}}</ref> It is also the most primal of the senses, as it is known to be the first indicator of safety or danger, therefore being the sense that drives the most basic of human survival skills. As such, it can be a catalyst for human behavior on a [[subconscious]] and [[instinct]]ive level.<ref>{{Cite journal|last=Bergland|first=Christopher|date=29 June 2015|title=Psychology Today|url=https://www.psychologytoday.com/us/blog/the-athletes-way/201506/how-does-scent-drive-human-behavior|journal=How Does Scent Drive Human Behavior?}}</ref>

=== Social ===
{{main|Social perception}}[[Social perception]] is the part of perception that allows people to understand the individuals and groups of their social world. Thus, it is an element of [[social cognition]].<ref>E. R. Smith, D. M. Mackie (2000). ''Social Psychology''. Psychology Press, 2nd ed., p. 20</ref>

==== Speech ====
{{main|Speech perception}}
[[File:Spectrogram_of_I_owe_you.png|right|thumb|Though the phrase "I owe you" can be heard as three distinct words, a [[spectrogram]] reveals no clear boundaries.]]
''Speech perception'' is the process by which [[spoken language]] is heard, interpreted and understood. Research in this field seeks to understand how human listeners recognize the sound of speech (or ''[[phonetics]]'') and use such information to understand spoken language.

Listeners manage to perceive words across a wide range of conditions, as the sound of a word can vary widely according to words that surround it and the [[tempo]] of the speech, as well as the physical characteristics, [[Accent (dialect)|accent]], [[Tone (linguistics)|tone]], and mood of the speaker. [[Reverberation]], signifying the persistence of sound after the sound is produced, can also have a considerable impact on perception. Experiments have shown that people automatically compensate for this effect when hearing speech.<ref name="eop_constancy" /><ref name="Watkins2010">{{cite book|chapter-url=https://books.google.com/books?id=ACkNL-G7gUUC&pg=PA440|title=The Neurophysiological Bases of Auditory Perception|last1=Watkins|first1=Anthony J.|last2=Raimond|first2=Andrew|last3=Makin|first3=Simon J.|date=23 March 2010|publisher=Springer|isbn=978-1-4419-5685-9|editor-last=Lopez-Poveda|editor-first=Enrique A.|page=440|chapter=Room reflection and constancy in speech-like sounds: Within-band effects|access-date=26 March 2011|archive-url=https://web.archive.org/web/20111109163241/http://books.google.com/books?id=ACkNL-G7gUUC&pg=PA440|archive-date=9 November 2011|url-status=live|bibcode=2010nbap.book.....L}}</ref>

The process of perceiving speech begins at the level of the sound within the auditory signal and the process of [[Hearing (sense)|audition]]. The initial auditory signal is compared with visual information—primarily lip movement—to extract acoustic cues and phonetic information. It is possible other sensory modalities are integrated at this stage as well.<ref>{{cite book|chapter-url=https://books.google.com/books?id=EwY15naRiFgC&q=%22Primacy+of+Multimodal+Speech+Perception%22&pg=PA51|title=The Handbook of Speech Perception|last=Rosenblum|first=Lawrence D.|editor1-last=Pisoni|editor1-first=David|page=51|chapter=Primacy of Multimodal Speech Perception|date=15 April 2008|publisher=John Wiley & Sons |isbn=978-0-470-75677-5|editor2-last=Remez|editor2-first=Robert}}</ref> This speech information can then be used for higher-level language processes, such as [[word recognition]].

Speech perception is not necessarily uni-directional. Higher-level language processes connected with [[Morphology (linguistics)|morphology]], [[syntax]], and/or [[semantics]] may also interact with basic speech perception processes to aid in recognition of speech sounds.<ref>{{cite journal |last1=Davis |first1=Matthew H. |last2=Johnsrude |first2=Ingrid S. |title=Hearing speech sounds: Top-down influences on the interface between audition and speech perception |journal=Hearing Research |date=July 2007 |volume=229 |issue=1–2 |pages=132–147 |doi=10.1016/j.heares.2007.01.014|pmid=17317056 |s2cid=12111361 }}</ref> It may be the case that it is not necessary (maybe not even possible) for a listener to recognize [[phoneme]]s before recognizing higher units, such as words. In an experiment, professor Richard M. Warren replaced one phoneme of a word with a cough-like sound. His subjects restored the missing speech sound perceptually without any difficulty. Moreover, they were not able to accurately identify which phoneme had even been disturbed.<ref>{{cite journal|last=Warren|first=R. M.|year=1970|title=Restoration of missing speech sounds|journal=Science|volume=167|issue=3917|pages=392–393|doi=10.1126/science.167.3917.392|pmid=5409744|bibcode=1970Sci...167..392W|s2cid=30356740}}</ref>

==== Faces ====
{{main|Face perception}}''Facial perception'' refers to cognitive processes specialized in handling [[human faces]] (including perceiving the identity of an individual) and facial expressions (such as emotional cues.){{Reference needed|date=March 2024}}

==== Social touch ====
{{main|Somatosensory system#Neural processing of social touch}}The ''somatosensory cortex'' is a part of the brain that receives and encodes sensory information from receptors of the entire body.<ref>{{Cite web|url=https://human-memory.net/somatosensory-cortex/|title=Somatosensory Cortex|date=31 October 2019|website=The Human Memory|access-date=8 March 2020}}</ref>

[[Affective|Affective touch]] is a type of sensory information that elicits an emotional reaction and is usually social in nature. Such information is actually coded differently than other sensory information. Though the intensity of affective touch is still encoded in the primary somatosensory cortex, the feeling of pleasantness associated with affective touch is activated more in the [[anterior cingulate cortex]]. Increased [[Blood-oxygen-level-dependent imaging|blood oxygen level-dependent]] (BOLD) contrast imaging, identified during [[functional magnetic resonance imaging]] (fMRI), shows that signals in the anterior cingulate cortex, as well as the [[prefrontal cortex]], are highly correlated with pleasantness scores of affective touch. Inhibitory [[transcranial magnetic stimulation]] (TMS) of the primary somatosensory cortex inhibits the perception of affective touch intensity, but not affective touch pleasantness. Therefore, the S1 is not directly involved in processing socially affective touch pleasantness, but still plays a role in discriminating touch location and intensity.<ref>{{cite journal|last1=Case|first1=LK|last2=Laubacher|first2=CM|last3=Olausson|first3=H|last4=Wang|first4=B|last5=Spagnolo|first5=PA|last6=Bushnell|first6=MC|title=Encoding of Touch Intensity But Not Pleasantness in Human Primary Somatosensory Cortex|journal=J Neurosci|volume=36|issue=21|pages=5850–60|doi=10.1523/JNEUROSCI.1130-15.2016|pmc=4879201|pmid=27225773|year=2016}}</ref>

=== Multi-modal perception ===
[[Multi-modal perception]] refers to concurrent stimulation in more than one sensory modality and the effect such has on the perception of events and objects in the world.<ref>{{Cite web|url=https://courses.lumenlearning.com/waymaker-psychology/chapter/multi-modal-perception/|title=Multi-Modal Perception|website=Lumen Waymaker|page=Introduction to Psychology|access-date=8 March 2020}}</ref>

==== Time (chronoception) ====
{{main|time perception}}
[[Time perception|Chronoception]] refers to how the passage of [[time]] is perceived and experienced. Although the [[Time perception|sense of time]] is not associated with a specific [[sensory system]], the work of [[psychologist]]s and [[neuroscientist]]s indicates that human brains do have a system governing the perception of time,<ref name="Rao 2001">{{cite journal|vauthors=Rao SM, Mayer AR, Harrington DL|date=March 2001|title=The evolution of brain activation during temporal processing|journal=Nature Neuroscience|volume=4|issue=3|pages=317–23|doi=10.1038/85191|pmid=11224550|s2cid=3570715|url=https://escholarship.org/uc/item/80c4d02m }}</ref><ref>{{cite web|url=http://www.unisci.com/stories/20011/0227013.htm|title=Brain Areas Critical To Human Time Sense Identified|date=2001-02-27|publisher=UniSci – Daily University Science News}}</ref> composed of a highly distributed system involving the [[cerebral cortex]], [[cerebellum]], and [[basal ganglia]]. One particular component of the brain, the [[suprachiasmatic nucleus]], is responsible for the [[circadian rhythm]] (commonly known as one's "internal clock"), while other cell clusters appear to be capable of shorter-range timekeeping, known as an ''[[ultradian]] rhythm''.

One or more [[dopaminergic pathways]] in the [[central nervous system]] appear to have a strong modulatory influence on [[mental chronometry]], particularly [[Interval (time)|interval timing.]]<ref name="Amph-DA reaction time">{{cite journal|vauthors=Parker KL, Lamichhane D, Caetano MS, Narayanan NS|date=October 2013|title=Executive dysfunction in Parkinson's disease and timing deficits|journal=Frontiers in Integrative Neuroscience|volume=7|pages=75|doi=10.3389/fnint.2013.00075|pmc=3813949|pmid=24198770|quote=Manipulations of dopaminergic signaling profoundly influence interval timing, leading to the hypothesis that dopamine influences internal pacemaker, or "clock", activity. For instance, amphetamine, which increases concentrations of dopamine at the synaptic cleft advances the start of responding during interval timing, whereas antagonists of D2 type dopamine receptors typically slow timing;... Depletion of dopamine in healthy volunteers impairs timing, while amphetamine releases synaptic dopamine and speeds up timing.|doi-access=free}}</ref>

==== Agency ====
{{main|Sense of agency}}

''Sense of agency'' refers to the subjective feeling of having chosen a particular action. Some conditions, such as [[schizophrenia]], can cause a loss of this sense, which may lead a person into delusions, such as feeling like a machine or like an outside source is controlling them. An opposite extreme can also occur, where people experience everything in their environment as though they had decided that it would happen.<ref>{{cite book|last=Metzinger|first=Thomas|title=The Ego Tunnel|publisher=Basic Books|year=2009|isbn=978-0-465-04567-9|pages=117–118}}</ref>

Even in non-[[Pathology|pathological]] cases, there is a measurable difference between the making of a decision and the feeling of agency. Through methods such as [[Neuroscience of free will#Libet experiment|the Libet experiment]], a gap of half a second or more can be detected from the time when there are detectable neurological signs of a decision having been made to the time when the subject actually becomes conscious of the decision.

There are also experiments in which an illusion of agency is induced in psychologically normal subjects. In 1999, psychologists [[Daniel Wegner|Wegner]] and Wheatley gave subjects instructions to move a mouse around a scene and point to an image about once every thirty seconds. However, a second person—acting as a test subject but actually a confederate—had their hand on the mouse at the same time, and controlled some of the movement. Experimenters were able to arrange for subjects to perceive certain "forced stops" as if they were their own choice.<ref>{{cite journal|vauthors=Wegner DM, Wheatley T|date=July 1999|title=Apparent mental causation. Sources of the experience of will|journal=The American Psychologist|volume=54|issue=7|pages=480–92|citeseerx=10.1.1.188.8271|doi=10.1037/0003-066x.54.7.480|pmid=10424155}}</ref><ref>{{cite book|last=Metzinger|first=Thomas|title=Being No One|date=2003|page=508}}</ref>

==== Familiarity ====

[[Recognition memory]] is sometimes divided into two functions by neuroscientists: ''familiarity'' and ''recollection''.<ref>{{cite journal|last=Mandler|year=1980|title=Recognizing: the judgement of prior occurrence|url=http://www.escholarship.org/uc/item/58b2c2fc|journal=Psychological Review|volume=87|issue=3|pages=252–271|doi=10.1037/0033-295X.87.3.252|s2cid=2166238 }}</ref> A strong sense of familiarity can occur without any recollection, for example in cases of [[deja vu]].

The [[temporal lobe]] (specifically the [[perirhinal cortex]]) responds differently to stimuli that feel novel compared to stimuli that feel familiar. [[Firing rate (cells)|Firing rates]] in the perirhinal cortex are connected with the sense of familiarity in humans and other mammals. In tests, stimulating this area at 10–15&nbsp;Hz caused animals to treat even novel images as familiar, and stimulation at 30–40&nbsp;Hz caused novel images to be partially treated as familiar.<ref>{{cite journal|vauthors=Ho JW, Poeta DL, Jacobson TK, Zolnik TA, Neske GT, Connors BW, Burwell RD|date=September 2015|title=Bidirectional Modulation of Recognition Memory|journal=The Journal of Neuroscience|volume=35|issue=39|pages=13323–35|doi=10.1523/JNEUROSCI.2278-15.2015|pmc=4588607|pmid=26424881}}</ref> In particular, stimulation at 30–40&nbsp;Hz led to animals looking at a familiar image for longer periods, as they would for an unfamiliar one, though it did not lead to the same exploration behavior normally associated with novelty.

Recent studies on [[lesion]]s in the area concluded that rats with a damaged perirhinal cortex were still more interested in exploring when novel objects were present, but seemed unable to tell novel objects from familiar ones—they examined both equally. Thus, other brain regions are involved with noticing unfamiliarity, while the perirhinal cortex is needed to associate the feeling with a specific source.<ref>{{cite journal|vauthors=Kinnavane L, Amin E, Olarte-Sánchez CM, Aggleton JP|date=November 2016|title=Detecting and discriminating novel objects: The impact of perirhinal cortex disconnection on hippocampal activity patterns|journal=Hippocampus|volume=26|issue=11|pages=1393–1413|doi=10.1002/hipo.22615|pmc=5082501|pmid=27398938}}</ref>

==== Sexual stimulation ====
{{Main|Sexual stimulation}}

[[Sexual stimulation]] is any [[Stimulation|stimulus]] (including bodily contact) that leads to, enhances, and maintains [[sexual arousal]], possibly even leading to [[orgasm]]. Distinct from the general sense of [[#Touch|touch]], sexual stimulation is strongly tied to [[Hormone|hormonal activity]] and chemical triggers in the body. Although sexual arousal may arise without [[physical stimulation]], achieving orgasm usually requires physical sexual stimulation (stimulation of the Krause-Finger [[Bulboid corpuscle|corpuscles]]<ref>{{Cite news|url=https://abdominalkey.com/sensory-corpuscles/|title=Sensory Corpuscles|date=2017-03-29|work=Abdominal Key|access-date=2018-07-13|vauthors=Themes UF}}</ref> found in erogenous zones of the body.)

=== Other senses ===
{{main|Sense}}Other senses enable perception of [[Balance (ability)|body balance]] (vestibular sense<ref>{{Cite web |title=Your 8 Senses |url=https://sensoryhealth.org/basic/your-8-senses |access-date=2024-05-06 |website=sensoryhealth.org |language=en}}</ref>); [[acceleration]], including [[gravity]]; [[Proprioception|position of body parts]] (proprioception sense<ref name="3DVAE" />). They can also enable perception of internal senses (interoception sense<ref>{{Cite web |title=Your 8 Senses |url=https://sensoryhealth.org/basic/your-8-senses |access-date=2024-05-06 |website=sensoryhealth.org |language=en}}</ref>), such as temperature, pain, [[suffocation]], [[Gag Reflex|gag reflex]], [[abdominal distension]], fullness of [[rectum]] and [[urinary bladder]], and sensations felt in the [[throat]] and [[lung]]s.

== Reality ==
In the case of visual perception, some people can see the percept shift in their [[mind's eye]].<ref name="Wettlaufer2003">{{Cite book|title=In the mind's eye : the visual impulse in Diderot, Baudelaire and Ruskin, pg. 257|last=Wettlaufer|first=Alexandra K.|publisher=Rodopi|year=2003|isbn=978-90-420-1035-2|location=Amsterdam}}</ref> Others, who are not [[Picture thinking|picture thinkers]], may not necessarily perceive the 'shape-shifting' as their world changes. This [[esemplastic]] nature has been demonstrated by an experiment that showed that [[ambiguous image]]s have multiple interpretations on the perceptual level.

The confusing ambiguity of perception is exploited in human technologies such as [[camouflage]] and biological [[mimicry]]. For example, the wings of [[European peacock|European peacock butterflies]] bear [[Eyespot (mimicry)|eyespots]] that birds respond to as though they were the eyes of a dangerous predator.

There is also evidence that the brain in some ways operates on a slight "delay" in order to allow nerve impulses from distant parts of the body to be integrated into simultaneous signals.<ref>[https://www.npr.org/templates/story/story.php?storyId=104183551 The Secret Advantage Of Being Short] {{webarchive|url=https://web.archive.org/web/20090521081301/http://www.npr.org/templates/story/story.php?storyId=104183551|date=21 May 2009}} by Robert Krulwich. ''All Things Considered'', NPR. 18 May 2009.</ref>

Perception is one of the oldest fields in psychology. The oldest [[Quantitative research|quantitative]] laws in psychology are [[Weber-Fechner law|Weber's law]], which states that the smallest noticeable difference in stimulus intensity is proportional to the intensity of the reference; and [[Weber-Fechner law|Fechner's law]], which quantifies the relationship between the intensity of the physical stimulus and its perceptual counterpart (e.g., testing how much darker a computer screen can get before the viewer actually notices). The study of perception gave rise to the [[Gestalt psychology|Gestalt School of Psychology]], with an emphasis on a [[Holism|holistic]] approach.

== Physiology ==
{{main|Sensory system}}A ''sensory system'' is a part of the nervous system responsible for processing [[Sense|sensory]] information. A sensory system consists of [[sensory receptor]]s, [[neural pathway]]s, and parts of the brain involved in sensory perception. Commonly recognized sensory systems are those for [[Vision (sense)|vision]], [[Hearing (sense)|hearing]], [[somatic sensation]] (touch), [[taste]] and [[olfaction]] (smell), as listed above. It has been suggested that the immune system is an overlooked sensory modality.<ref>{{cite journal|last=Bedford|first=F. L.|author-link=Felice Bedford|year=2011|title=The missing sensory modality: the immune system|journal=Perception|volume=40|issue=10|pages=1265–1267|doi=10.1068/p7119|pmid=22308900|s2cid=9546850}}</ref> In short, senses are [[transducers]] from the physical world to the realm of the mind.

The [[receptive field]] is the specific part of the world to which a receptor organ and receptor cells respond. For instance, the part of the world an eye can see, is its receptive field; the light that each [[Rod cell|rod]] or [[Cone cell|cone]] can see, is its receptive field.<ref>Kolb & Whishaw: ''Fundamentals of Human Neuropsychology'' (2003)</ref> Receptive fields have been identified for the [[visual system]], [[auditory system]] and [[somatosensory system]], so far. Research attention is currently focused not only on external perception processes, but also to "[[interoception]]", considered as the process of receiving, accessing and appraising internal bodily signals. Maintaining desired physiological states is critical for an organism's well-being and survival. Interoception is an iterative process, requiring the interplay between perception of body states and awareness of these states to generate proper self-regulation. Afferent sensory signals continuously interact with higher order cognitive representations of goals, history, and environment, shaping emotional experience and motivating regulatory behavior.<ref>{{cite journal|author1=Farb N.|author2=Daubenmier J.|author3=Price C. J.|author4=Gard T.|author5=Kerr C.|author6=Dunn B. D.|author7=Mehling W. E.|year=2015|title=Interoception, contemplative practice, and health|journal=Frontiers in Psychology|volume=6|page=763|doi=10.3389/fpsyg.2015.00763|pmc=4460802|pmid=26106345|doi-access=free}}</ref>

== Features ==

=== Constancy ===
{{main|Subjective constancy|}}''Perceptual constancy'' is the ability of perceptual systems to recognize the same object from widely varying sensory inputs.<ref name="Bernstein20102"/>{{rp|118–120}}<ref name="AtkinsonAtkinson1990">{{cite book|url=https://books.google.com/books?id=Nw54PwAACAAJ|title=Introduction to psychology|last1=Atkinson|first1=Rita L.|last2=Atkinson|first2=Richard C.|last3=Smith|first3=Edward E.|date=March 1990|publisher=Harcourt Brace Jovanovich|isbn=978-0-15-543689-3|pages=177–183|access-date=24 March 2011|archive-url=https://web.archive.org/web/20111109162907/http://books.google.com/books?id=Nw54PwAACAAJ|archive-date=9 November 2011|url-status=live}}</ref> For example, individual people can be recognized from views, such as frontal and profile, which form very different shapes on the retina. A coin looked at face-on makes a circular image on the retina, but when held at angle it makes an elliptical image.<ref name="eop_constancy">{{cite book|chapter-url=https://books.google.com/books?id=Y4TOEN4f5ZMC&pg=PA136|title=Encyclopedia of Perception|last=Moore|first=Brian C. J.|date=15 October 2009|publisher=Sage|isbn=978-1-4129-4081-8|editor-last=Goldstein|editor-first=E. Bruce|pages=136–137|chapter=Audition|access-date=26 March 2011|archive-url=https://web.archive.org/web/20111109162606/http://books.google.com/books?id=Y4TOEN4f5ZMC&pg=PA136|archive-date=9 November 2011|url-status=live}}</ref> In normal perception these are recognized as a single three-dimensional object. Without this correction process, an animal approaching from the distance would appear to gain in size.<ref name="Sonderegger1998">{{cite book|url=https://books.google.com/books?id=UUrCHiSb_QsC&pg=PA45|title=Psychology|last=Sonderegger|first=Theo|date=16 October 1998|publisher=John Wiley and Sons|isbn=978-0-8220-5327-9|pages=43–46|access-date=24 March 2011|archive-url=https://web.archive.org/web/20111109162741/http://books.google.com/books?id=UUrCHiSb_QsC&pg=PA45|archive-date=9 November 2011|url-status=live}}</ref><ref name="enc_constancy">{{cite book|chapter-url=https://books.google.com/books?id=Y4TOEN4f5ZMC&pg=PA309|title=Encyclopedia of Perception|last=Goldstein|first=E. Bruce|date=15 October 2009|publisher=Sage|isbn=978-1-4129-4081-8|editor-last=Goldstein|editor-first=E. Bruce|pages=309–313|chapter=Constancy|access-date=26 March 2011|archive-url=https://web.archive.org/web/20111109162834/http://books.google.com/books?id=Y4TOEN4f5ZMC&pg=PA309|archive-date=9 November 2011|url-status=live}}</ref> One kind of perceptual constancy is ''[[color constancy]]'': for example, a white piece of paper can be recognized as such under different colors and intensities of light.<ref name="enc_constancy" /> Another example is ''roughness constancy'': when a hand is drawn quickly across a surface, the touch nerves are stimulated more intensely. The brain compensates for this, so the speed of contact does not affect the perceived roughness.<ref name="enc_constancy" /> Other constancies include melody, odor, brightness and words.<ref name="Roeckelein2006">{{cite book|url=https://books.google.com/books?id=1Yn6NZgxvssC&pg=PA126|title=Elsevier's dictionary of psychological theories|last=Roeckelein|first=Jon E.|publisher=Elsevier|year=2006|isbn=978-0-444-51750-0|page=126|access-date=24 March 2011|archive-url=https://web.archive.org/web/20111109162549/http://books.google.com/books?id=1Yn6NZgxvssC&pg=PA126|archive-date=9 November 2011|url-status=live}}</ref> These constancies are not always total, but the variation in the percept is much less than the variation in the physical stimulus.<ref name="enc_constancy" /> The perceptual systems of the brain achieve perceptual constancy in a variety of ways, each specialized for the kind of information being processed,<ref name="Yantis2001">{{cite book|url=https://books.google.com/books?id=GpGvYSTk9gYC&pg=PA7|title=Visual perception: essential readings|last=Yantis|first=Steven|publisher=Psychology Press|year=2001|isbn=978-0-86377-598-7|page=7|access-date=24 March 2011|archive-url=https://web.archive.org/web/20111109162254/http://books.google.com/books?id=GpGvYSTk9gYC&pg=PA7|archive-date=9 November 2011|url-status=live}}</ref> with [[Phonemic restoration effect|phonemic restoration]] as a notable example from hearing.

=== Grouping (Gestalt) ===
{{main|Principles of grouping}}
[[File:Gestalt closure.svg|right|thumb|Law of Closure. The human brain tends to perceive complete shapes even if those forms are incomplete.]]
The ''principles of grouping'' (or ''Gestalt laws of grouping'') are a set of principles in [[psychology]], first proposed by [[Gestalt psychology|Gestalt psychologists]], to explain how humans naturally perceive objects with patterns and objects. Gestalt psychologists argued that these principles exist because the mind has an innate disposition to [[perceive]] patterns in the stimulus based on certain rules. These principles are [[Principles of grouping|organized into six categories]]:

# '''Proximity''': the principle of ''[[Proximity principle|proximity]]'' states that, [[Ceteris paribus|all else being equal]], perception tends to group stimuli that are close together as part of the same object, and [[Stimulus (psychology)|stimuli]] that are far apart as two separate objects.
# '''Similarity''': the principle of ''[[Similarity (psychology)|similarity]]'' states that, all else being equal, perception lends itself to seeing stimuli that physically resemble each other as part of the same object and that are different as part of a separate object. This allows for people to distinguish between adjacent and overlapping objects based on their [[Texture (visual arts)#Visual texture|visual texture]] and [[Nominalism|resemblance]].
# '''Closure''': the principle of ''[[Closure (psychology)|closure]]'' refers to the mind's tendency to see complete figures or forms even if a picture is incomplete, partially hidden by other objects, or if part of the information needed to make a complete picture in our minds is missing. For example, if part of a shape's border is missing people still tend to see the shape as completely enclosed by the border and ignore the gaps.
# '''Good Continuation:''' the principle of ''[[Principles of grouping#Good continuation|good continuation]]'' makes sense of stimuli that overlap: when there is an intersection between two or more objects, people tend to perceive each as a single uninterrupted object.
# '''Common Fate''': the principle of ''[[Principles of grouping#Common fate|common fate]]'' groups stimuli together on the basis of their movement. When visual elements are seen moving in the same direction at the same rate, perception associates the movement as part of the same stimulus. This allows people to make out moving objects even when other details, such as color or outline, are obscured.
# The principle of ''[[Principles of grouping#Good form|good form]]'' refers to the tendency to group together forms of similar shape, pattern, [[color]], etc.<ref>Gray, Peter O. (2006): ''Psychology'', 5th ed., New York: Worth, p. 281. {{ISBN|978-0-7167-0617-5}}</ref><ref>{{cite book|title=Sensation and Perception|author1-link=Jeremy M. Wolfe|last1=Wolfe|first1=Jeremy M.|last2=Kluender|first2=Keith R.|last3=Levi|first3=Dennis M.|last4=Bartoshuk|first4=Linda M.|last5=Herz|first5=Rachel S.|last6=Klatzky|first6=Roberta L.|last7=Lederman|first7=Susan J.|publisher=Sinauer Associates|year=2008|isbn=978-0-87893-938-1|edition=2nd|pages=78, 80|chapter=Gestalt Grouping Principles|chapter-url=http://www.sinauer.com./wolfe/chap4/gestaltF.htm|archive-url=https://web.archive.org/web/20110723150836/http://www.sinauer.com/wolfe/chap4/gestaltF.htm|archive-date=23 July 2011|url-status=dead}}</ref><ref>Goldstein (2009). pp. 105–107</ref><ref>{{cite encyclopaedia|encyclopedia=Encyclopaedic Dictionary of Psychological Terms|first=J. C.|last=Banerjee|publisher=M.D. Publications Pvt. Ltd|year=1994|isbn=978-81-85880-28-0|article=Gestalt Theory of Perception|pages=107–108}}</ref>

Later research has identified additional grouping principles.<ref>{{cite book|title=Psychology: themes and variations|last=Weiten|first=Wayne|publisher=Brooks/Cole Pub. Co.|year=1998|isbn=978-0-534-34014-8|edition=4th|page=144}}</ref>

=== Contrast effects ===
{{main|Contrast effect}}A common finding across many different kinds of perception is that the perceived qualities of an object can be affected by the qualities of context. If one object is extreme on some dimension, then neighboring objects are perceived as further away from that extreme.

"[[Contrast effect#Types|Simultaneous contrast effect]]" is the term used when stimuli are presented at the same time, whereas ''[[successive contrast]]'' applies when stimuli are presented one after another.<ref name="Corsini2002">{{cite book|url=https://books.google.com/books?id=0uxnglHzYaoC&pg=PA219|title=The dictionary of psychology|last=Corsini|first=Raymond J.|publisher=Psychology Press|year=2002|isbn=978-1-58391-328-4|page=219|access-date=24 March 2011|archive-url=https://web.archive.org/web/20111109162655/http://books.google.com/books?id=0uxnglHzYaoC&pg=PA219|archive-date=9 November 2011|url-status=live}}</ref>

The contrast effect was noted by the 17th Century philosopher [[John Locke]], who observed that lukewarm water can feel hot or cold depending on whether the hand touching it was previously in hot or cold water.<ref name="Kushner2008">{{cite book|url=https://books.google.com/books?id=TYn5VHp9jioC&pg=PA1|title=Contrast in judgments of mental health|last=Kushner|first=Laura H.|year=2008|isbn=978-0-549-91314-6|page=1|access-date=24 March 2011|archive-url=https://web.archive.org/web/20111109163219/http://books.google.com/books?id=TYn5VHp9jioC&pg=PA1|archive-date=9 November 2011|url-status=live}}</ref> In the early 20th Century, [[Wilhelm Wundt]] identified contrast as a fundamental principle of perception, and since then the effect has been confirmed in many different areas.<ref name="Kushner2008" /> These effects shape not only visual qualities like color and brightness, but other kinds of perception, including how heavy an object feels.<ref name="Plous1993">{{cite book|url=https://books.google.com/books?id=xvWOQgAACAAJ|title=The psychology of judgment and decision making|last=Plous|first=Scott|publisher=McGraw-Hill|year=1993|isbn=978-0-07-050477-6|pages=38–41|access-date=24 March 2011|archive-url=https://web.archive.org/web/20111109162735/http://books.google.com/books?id=xvWOQgAACAAJ|archive-date=9 November 2011|url-status=live}}</ref> One experiment found that thinking of the name "Hitler" led to subjects rating a person as more hostile.<ref name="Moskowitz2005">{{cite book|url=https://books.google.com/books?id=_-NLW8Ynvp8C&pg=PA421|title=Social cognition: understanding self and others|last=Moskowitz|first=Gordon B.|publisher=Guilford Press|year=2005|isbn=978-1-59385-085-2|page=421|access-date=24 March 2011|archive-url=https://web.archive.org/web/20111109163155/http://books.google.com/books?id=_-NLW8Ynvp8C&pg=PA421|archive-date=9 November 2011|url-status=live}}</ref> Whether a piece of music is perceived as good or bad can depend on whether the music heard before it was pleasant or unpleasant.<ref name="Popper2010">{{cite book|url=https://books.google.com/books?id=ZYXd3CF1_vkC&pg=PA150|title=Music Perception|last=Popper|first=Arthur N.|date=30 November 2010|publisher=Springer|isbn=978-1-4419-6113-6|page=150|access-date=24 March 2011|archive-url=https://web.archive.org/web/20111109163046/http://books.google.com/books?id=ZYXd3CF1_vkC&pg=PA150|archive-date=9 November 2011|url-status=live}}</ref> For the effect to work, the objects being compared need to be similar to each other: a television reporter can seem smaller when interviewing a tall basketball player, but not when standing next to a tall building.<ref name="Plous1993" /> In the brain, brightness contrast exerts effects on both neuronal [[Firing rate (cells)|firing rates]] and [[Neuronal synchronization|neuronal synchrony]].<ref>{{cite journal|last1=Biederlack|first1=J.|last2=Castelo-Branco|first2=M.|last3=Neuenschwander|first3=S.|last4=Wheeler|first4=D.W.|last5=Singer|first5=W.|last6=Nikolić|first6=D.|year=2006|title=Brightness induction: Rate enhancement and neuronal synchronization as complementary codes|journal=Neuron|volume=52|issue=6|pages=1073–1083|doi=10.1016/j.neuron.2006.11.012|pmid=17178409|s2cid=16732916|doi-access=free}}</ref>

== Theories ==
=== Perception as direct perception (Gibson) ===
[[Cognitivism (psychology)|Cognitive theories]] of perception assume there is a [[poverty of the stimulus]]. This is the claim that [[wikt:sensation|sensations]], by themselves, are unable to provide a unique description of the world.<ref>Stone, James V. (2012): "[https://books.google.com/books?id=HZf6AQAAQBAJ Vision and Brain: How we perceive the world]", Cambridge, MIT Press, pp. 155–178.</ref> Sensations require 'enriching', which is the role of the [[mental model]].

The [[Ecological psychology|perceptual ecology]] approach was introduced by professor [[James J. Gibson]], who rejected the assumption of a [[poverty of stimulus]] and the idea that perception is based upon sensations. Instead, Gibson investigated what information is actually presented to the perceptual systems. His theory "assumes the existence of stable, unbounded, and permanent stimulus-information in the [[ambient optic array]]. And it supposes that the visual system can explore and detect this information. The theory is information-based, not sensation-based."<ref>Gibson, James J. (2002): "[https://web.archive.org/web/20181106171520/https://pdfs.semanticscholar.org/f594/23f1a766380ff945fc401b976618a2b2a92a.pdf A Theory of Direct Visual Perception]". In: Alva Noë/Evan Thompson (Eds.), ''Vision and Mind. Selected Readings in the Philosophy of Perception'', Cambridge, MIT Press, pp. 77–89.</ref> He and the psychologists who work within this [[paradigm]] detailed how the world could be specified to a mobile, exploring organism via the lawful projection of information about the world into energy arrays.<ref>{{cite book|url=https://books.google.com/books?id=NIEJt5afhwgC|title=Phenomenology of the Human Person|last=Sokolowski|first=Robert|publisher=Cambridge University Press|year=2008|isbn=978-0-521-71766-3|location=New York|pages=199–200|archive-url=https://web.archive.org/web/20150925011659/https://books.google.com/books?id=NIEJt5afhwgC&printsec=frontcover|archive-date=25 September 2015|url-status=live}}</ref> "Specification" would be a 1:1 mapping of some aspect of the world into a perceptual array. Given such a mapping, no enrichment is required and perception is [[direct perception|direct]].<ref>{{cite journal|last=Richards|first=Robert J.|date=December 1976|title=James Gibson's Passive Theory of Perception: A Rejection of the Doctrine of Specific Nerve Energies|url=http://philosophy.uchicago.edu/faculty/files/richards/James%20Gibson%27s%20Passive%20Theory%20of%20Perception.pdf|url-status=dead|journal=Philosophy and Phenomenological Research|volume=37|issue=2|pages=218–233|doi=10.2307/2107193|archive-url=https://web.archive.org/web/20130613180128/http://philosophy.uchicago.edu/faculty/files/richards/James%20Gibson%27s%20Passive%20Theory%20of%20Perception.pdf|archive-date=13 June 2013|jstor=2107193|access-date=15 February 2013}}</ref>

=== Perception-in-action ===
From Gibson's early work derived an ecological understanding of perception known as ''perception-in-action,'' which argues that perception is a requisite property of animate action. It posits that, without perception, action would be unguided, and without action, perception would serve no purpose. Animate actions require both perception and motion, which can be described as "two sides of the same coin, the coin is action." Gibson works from the assumption that singular entities, which he calls ''invariants,'' already exist in the real world and that all that the perception process does is home in upon them.

The [[Constructive perception|constructivist view]], held by such philosophers as [[Ernst von Glasersfeld]], regards the continual adjustment of perception and action to the external input as precisely what constitutes the "entity," which is therefore far from being invariant.<ref>Consciousness in Action, S. L. Hurley, illustrated, [[Harvard University Press]], 2002, 0674007964, pp. 430–432.</ref> Glasersfeld considers an ''invariant'' as a target to be homed in upon, and a pragmatic necessity to allow an initial measure of understanding to be established prior to the updating that a statement aims to achieve. The invariant does not, and need not, represent an actuality. Glasersfeld describes it as extremely unlikely that what is desired or [[Fear processing in the brain|feared]] by an organism will never suffer change as time goes on. This [[social constructionist]] theory thus allows for a needful evolutionary adjustment.<ref>Glasersfeld, Ernst von (1995), ''Radical Constructivism: A Way of Knowing and Learning,'' London: RoutledgeFalmer; Poerksen, Bernhard (ed.) (2004), ''[https://books.google.com/books?id=8-_EsHHxHYcC The Certainty of Uncertainty: Dialogues Introducing Constructivism],'' Exeter: Imprint Academic; Wright. Edmond (2005). ''Narrative, Perception, Language, and Faith,'' Basingstoke: [[Palgrave Macmillan]].</ref>

A mathematical theory of perception-in-action has been devised and investigated in many forms of controlled movement, and has been described in many different species of organism using the [[General Tau Theory]]. According to this theory, "tau information", or time-to-goal information is the fundamental ''percept'' in perception.

=== Evolutionary psychology ===
Many philosophers, such as [[Jerry Fodor]], write that the purpose of perception is knowledge. However, [[Evolutionary psychology|evolutionary psychologists]] hold that the primary purpose of perception is to guide action.<ref name="Gaulin 4">Gaulin, Steven J. C. and Donald H. McBurney. Evolutionary Psychology. [[Prentice Hall]]. 2003. {{ISBN|978-0-13-111529-3}}, Chapter 4, pp. 81–101.</ref> They give the example of [[depth perception]], which seems to have evolved not to aid in knowing the distances to other objects but rather to aid movement.<ref name="Gaulin 4" /> Evolutionary psychologists argue that animals ranging from [[fiddler crab]]s to humans use eyesight for [[Collision avoidance in transportation|collision avoidance]], suggesting that vision is basically for directing action, not providing knowledge.<ref name="Gaulin 4" /> [[Neuropsychology|Neuropsychologists]] showed that perception systems evolved along the specifics of animals' activities. This explains why bats and worms can perceive different frequency of auditory and visual systems than, for example, humans.

Building and maintaining sense organs is [[metabolically]] expensive. More than half the brain is devoted to processing sensory information, and the brain itself consumes roughly one-fourth of one's metabolic resources. Thus, such organs evolve only when they provide exceptional benefits to an organism's fitness.<ref name="Gaulin 4" />

Scientists who study perception and sensation have long understood the human senses as adaptations.<ref name="Gaulin 4" /> Depth perception consists of processing over half a dozen visual cues, each of which is based on a regularity of the physical world.<ref name="Gaulin 4" /> Vision evolved to respond to the narrow range of electromagnetic energy that is plentiful and that does not pass through objects.<ref name="Gaulin 4" /> Sound waves provide useful information about the sources of and distances to objects, with larger animals making and hearing lower-frequency sounds and smaller animals making and hearing higher-frequency sounds.<ref name="Gaulin 4" /> Taste and smell respond to chemicals in the environment that were significant for fitness in the environment of evolutionary adaptedness.<ref name="Gaulin 4" /> The sense of touch is actually many senses, including pressure, heat, cold, tickle, and pain.<ref name="Gaulin 4" /> Pain, while unpleasant, is adaptive.<ref name="Gaulin 4" /> An important adaptation for senses is range shifting, by which the organism becomes temporarily more or less sensitive to sensation.<ref name="Gaulin 4" /> For example, one's eyes automatically adjust to dim or bright ambient light.<ref name="Gaulin 4" /> Sensory abilities of different organisms often co-evolve, as is the case with the hearing of echolocating bats and that of the moths that have evolved to respond to the sounds that the bats make.<ref name="Gaulin 4" />

Evolutionary psychologists claim that perception demonstrates the principle of modularity, with specialized mechanisms handling particular perception tasks.<ref name="Gaulin 4" /> For example, people with damage to a particular part of the brain are not able to recognize faces (''[[prosopagnosia]]'').<ref name="Gaulin 4" /> Evolutionary psychology suggests that this indicates a so-called face-reading module.<ref name="Gaulin 4" />

=== Closed-loop perception ===
The theory of [[closed-loop transfer function|closed-loop perception]] proposes dynamic motor-sensory closed-loop process in which information flows through the environment and the brain in continuous loops.<ref name="Dewey1">{{cite journal |author=Dewey J |year=1896 |title=The reflex arc concept in psychology |url=https://pdfs.semanticscholar.org/a7ab/dafa9cca3547d8f441ee9dc3b5ad19ee7f59.pdf |url-status=dead |journal=[[Psychological Review]] |volume=3 |issue=4 |pages=359–370 |doi=10.1037/h0070405 |archive-url=https://web.archive.org/web/20181106132335/https://pdfs.semanticscholar.org/a7ab/dafa9cca3547d8f441ee9dc3b5ad19ee7f59.pdf |archive-date=2018-11-06 |s2cid=14028152}}</ref><ref name="Friston1">Friston, K. (2010) [http://bdl.kaist.ac.kr/lecture/2011springbis525/10%20(2010)%20The%20free-energy%20principle-%20a%20unified%20brain%20theory.pdf The free-energy principle: a unified brain theory?] {{Webarchive|url=https://web.archive.org/web/20170808232006/http://bdl.kaist.ac.kr/lecture/2011springbis525/10%20(2010)%20The%20free-energy%20principle-%20a%20unified%20brain%20theory.pdf |date=8 August 2017 }} nature reviews neuroscience 11:127-38</ref><ref name="Tishby1">Tishby, N. and D. Polani, [http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.259.8031&rep=rep1&type=pdf Information theory of decisions and actions], in Perception-Action Cycle. 2011, Springer. p. 601–636.</ref><ref name="AhiAssa1">{{cite journal |author=Ahissar E., Assa E. |year=2016 |title=Perception as a closed-loop convergence process |journal=[[eLife]] |volume=5 |article-number=e12830 |doi=10.7554/eLife.12830 |pmc=4913359 |pmid=27159238 |doi-access=free}}{{Creative Commons text attribution notice|cc=by4|from this source=yes}}</ref> Closed-loop perception appears consistent with anatomy and with the fact that perception is typically an incremental process. Repeated encounters with an object, whether conscious or not, enable an animal to refine its impressions of that object. This can be achieved more easily with a circular closed-loop system than with a linear open-loop one. Closed-loop perception can explain many of the phenomena that open-loop perception struggles to account for. This is largely because closed-loop perception considers motion to be an integral part of perception, and not an interfering component that must be corrected for. Furthermore, an environment perceived via sensor motion, and not despite sensor motion, need not be further stabilized by internal processes.<ref name="AhiAssa1" />

=== Feature integration theory ===
{{Main|Feature integration theory}}
[[Anne Treisman]]'s feature integration theory (FIT) attempts to explain how characteristics of a stimulus such as physical location in space, motion, color, and shape are merged to form one percept despite each of these characteristics activating separate areas of the cortex. FIT explains this through a two part system of perception involving the preattentive and focused attention stages.<ref name=":0">{{Cite book |last=Goldstein |first=E. Bruce |title=Cognitive Psychology: Connecting Mind, Research, and Everyday Experience, 4th Edition |publisher=[[Cengage Learning]] |year=2015 |isbn=978-1-285-76388-0 |location=Stamford, CT |pages=109–112}}</ref><ref>{{Cite journal |last1=Treisman |first1=Anne |last2=Gelade |first2=Garry |date=1980 |title=A Feature-Integration Theory of Attention |url=http://homepage.psy.utexas.edu/homepage/class/Psy355/Gilden/treisman.pdf |journal=Cognitive Psychology |volume=12 |issue=1 |pages=97–136 |doi=10.1016/0010-0285(80)90005-5 |pmid=7351125 |archive-url=https://web.archive.org/web/20080905025042/http://homepage.psy.utexas.edu/homepage/class/Psy355/Gilden/treisman.pdf |archive-date=5 September 2008 |via=[[Science Direct]] |s2cid=353246}}</ref><ref name=":1">{{Cite book|last=Goldstein|first=E. Bruce|title=Sensation and Perception|publisher=Cengage Learning|year=2010|isbn=978-0-495-60149-4|location=Belmont, CA|pages=144–146|edition=8th}}</ref><ref name=":2">{{Cite journal|last1=Treisman|first1=Anne|last2=Schmidt|first2=Hilary|date=1982|title=Illusory Conjunctions in the Perception of Objects|url=https://www.sciencedirect.com/science/article/abs/pii/0010028582900068|journal=Cognitive Psychology|volume=14|issue=1|pages=107–141|doi=10.1016/0010-0285(82)90006-8|pmid=7053925|s2cid=11201516|via=Science Direct|url-access=subscription}}</ref><ref name=":3">{{Cite journal|last=Treisman|first=Anne|date=1977|title=Focused Attention in The Perception and Retrieval of Multidimensional Stimuli|url=https://www.sciencedirect.com/science/article/abs/pii/0010028582900068|journal=Cognitive Psychology|volume=14|issue=1|pages=107–141|doi=10.1016/0010-0285(82)90006-8|pmid=7053925|s2cid=11201516|via=Science Direct|url-access=subscription}}</ref>

The preattentive stage of perception is largely unconscious, and analyzes an object by breaking it down into its basic features, such as the specific color, geometric shape, motion, depth, individual lines, and many others.<ref name=":0" /> Studies have shown that, when small groups of objects with different features (e.g., red triangle, blue circle) are briefly flashed in front of human participants, many individuals later report seeing shapes made up of the combined features of two different stimuli, thereby referred to as [[illusory conjunctions]].<ref name=":0" /><ref name=":2" />

The unconnected features described in the preattentive stage are combined into the objects one normally sees during the focused attention stage.<ref name=":0" /> The focused attention stage is based heavily around the idea of attention in perception and 'binds' the features together onto specific objects at specific spatial locations (see the [[binding problem]]).<ref name=":0" /><ref name=":3" />

=== Shared Intentionality theory ===
{{Main|Shared intentionality}}
A fundamentally different approach to understanding the perception of objects relies upon the essential role of [[Shared intentionality]].<ref>Tomasello, M. (1999). ''The Cultural Origins of Human Cognition.'' Cambridge, Massachusetts: Harvard University Press. 1999.</ref> Cognitive psychologist professor [[Michael Tomasello]] hypothesized that social bonds between children and caregivers would gradually increase through the essential motive force of shared intentionality beginning from birth.<ref>Tomasello, M. (2019). ''Becoming Human: A Theory of Ontogeny''. Cambridge, Massachusetts: [[Harvard University Press]].</ref> The notion of shared intentionality, introduced by Michael Tomasello, was developed by later researchers, who tended to explain this collaborative interaction from different perspectives, e.g., [[psychophysiology]],<ref>Val Danilov, I. & Mihailova, S. (2023). "Empirical Evidence of Shared Intentionality: Towards Bioengineering Systems Development." ''OBM Neurobiology'' 2023; 7(2): 167; doi:10.21926/obm.neurobiol.2302167. https://www.lidsen.com/journals/neurobiology/neurobiology-07-02-167</ref><ref>McClung, J. S., Placì, S., Bangerter, A., Clément, F., & Bshary, R. (2017). "The language of cooperation: shared intentionality drives variation in helping as a function of group membership." ''Proceedings of the Royal Society B: Biological Sciences,'' 284(1863), 20171682. http://dx.doi.org/10.1098/rspb.2017.1682.</ref><ref>Shteynberg, G., & Galinsky, A. D. (2011). "Implicit coordination: Sharing goals with similar others intensifies goal pursuit." ''Journal of Experimental Social Psychology,'' 47(6), 1291-1294., https://doi.org/10.1016/j.jesp.
2011.04.012.</ref> and neurobiology.<ref>Fishburn, F. A., Murty, V. P., Hlutkowsky, C. O., MacGillivray, C. E., Bemis, L. M., Murphy, M. E., ... & Perlman, S. B. (2018). "Putting our heads together: interpersonal neural synchronization as a biological mechanism for shared intentionality." ''Social cognitive and affective neuroscience,'' 13(8), 841-849.</ref> The [[Shared intentionality]] approach considers perception occurrence at an earlier stage of organisms' development than other theories, even before the emergence of [[Intentionality]]. Because many theories build their knowledge about perception based on its main features of the organization, identification, and interpretation of sensory information to represent the holistic picture of the environment, [[Intentionality]] is the central issue in perception development. Nowadays, only one hypothesis attempts to explain [[Shared intentionality]] in all its integral complexity from the level of interpersonal dynamics to interaction at the neuronal level. Introduced by Latvian professor Igor Val Danilov, the hypothesis of neurobiological processes occurring during Shared intentionality<ref>{{cite journal |title=Theoretical Grounds of Shared Intentionality for Neuroscience in Developing Bioengineering Systems |first=Igor |last=Val Danilov |journal=OBM Neurobiology |url= https://www.lidsen.com/journals/neurobiology/neurobiology-07-01-156 |date=2023-02-17 |volume=7 |issue=1 |page=156 |doi=10.21926/obm.neurobiol.2301156|doi-access=free }}</ref> highlights that, at the beginning of cognition, very young organisms cannot distinguish relevant sensory stimuli independently. Because the environment is the cacophony of stimuli (electromagnetic waves, chemical interactions, and pressure fluctuations), their sensation is too limited by the noise to solve the cue problem. The relevant stimulus cannot overcome the noise magnitude if it passes through the senses. Therefore, [[Intentionality]] is a difficult problem for them since it needs the representation of the environment already categorized into objects (see also [[binding problem]]). The perception of objects is also problematic since it cannot appear without Intentionality. From the perspective of this hypothesis, [[Shared intentionality]] is collaborative interactions in which participants share the essential sensory stimulus of the actual cognitive problem. This social bond enables ecological training of the young immature organism, starting at the reflexes stage of development, for processing the organization, identification, and interpretation of sensory information in developing perception.<ref>{{Cite journal |last=Val Danilov |first=Igor |date= 2023|title=Shared Intentionality Modulation at the Cell Level: Low-Frequency Oscillations for Temporal Coordination in Bioengineering Systems |url=https://www.lidsen.com/journals/neurobiology/neurobiology-07-04-185 |journal=OBM Neurobiology |language=en |volume=7 |issue=4 |pages=1–17 |doi=10.21926/obm.neurobiol.2304185|doi-access=free }}</ref> From this account perception emerges due to [[Shared intentionality]] in the embryonic stage of development, i.e., even before birth.<ref>{{Cite journal |last=Val Danilov |first=Igor |date= 2023|title=Low-Frequency Oscillations for Nonlocal Neuronal Coupling in Shared Intentionality Before and After Birth: Toward the Origin of Perception |url=https://www.lidsen.com/journals/neurobiology/neurobiology-07-04-192 |journal=OBM Neurobiology |language=en |volume=7 |issue=4 |pages=1–17 |doi=10.21926/obm.neurobiol.2304192|doi-access=free }}</ref>

=== Other theories of perception ===
* [[Enactivism]]
* [[Interactive activation and competition networks|The Interactive Activation and Competition Model]]
* [[Recognition-by-components theory|Recognition-By-Components Theory]] ([[Irving Biederman]])

== Effects on perception ==

=== Effect of experience ===
{{main|Perceptual learning}}With experience, [[organism]]s can learn to make finer perceptual distinctions, and learn new kinds of categorization. Wine-tasting, the reading of X-ray images and music appreciation are applications of this process in the [[human]] sphere. [[Research]] has focused on the relation of this to other kinds of [[learning]], and whether it takes place in peripheral [[Sensory perception|sensory]] systems or in the brain's processing of sense information.<ref>{{cite journal |last1=Sumner |first1=Meghan |last2=Samuel |first2=Arthur G. |url=https://web.stanford.edu/~sumner/Publications/2009_Sumner_JML.pdf |title=The Effect of Experience on the Perception and Representation of Dialect Variants |journal=Journal of Memory and Language |publisher=[[Elsevier Inc.]] |date=May 2009 |volume=60 |issue=4 |pages=487–501 |doi=10.1016/j.jml.2009.01.001 |access-date=3 June 2015 |archive-url=https://web.archive.org/web/20160202011511/https://web.stanford.edu/~sumner/Publications/2009_Sumner_JML.pdf |archive-date=2 February 2016 |url-status=live}}</ref> [[Empirical]] [[research]] show that specific practices (such as [[yoga]], [[mindfulness]], [[Tai chi|Tai Chi]], [[meditation]], Daoshi and other mind-body disciplines) can modify human perceptual modality. Specifically, these practices enable perception skills to switch from the external (exteroceptive field) towards a higher ability to focus on internal signals (''[[proprioception]]''). Also, when asked to provide verticality judgments, highly self-transcendent [[yoga]] practitioners were significantly less influenced by a misleading visual context. Increasing self-transcendence may enable yoga practitioners to optimize verticality judgment tasks by relying more on internal (vestibular and proprioceptive) signals coming from their own body, rather than on exteroceptive, visual cues.<ref>{{cite journal |last1=Fiori |first1=Francesca |last2=David |first2=Nicole |last3=Aglioti |first3=Salvatore Maria |date=2014 |title=Processing of proprioceptive and vestibular body signals and self-transcendence in Ashtanga yoga practitioners |journal=[[Frontiers in Human Neuroscience]] |volume=8 |pages=734 |doi=10.3389/fnhum.2014.00734 |pmc=4166896 |pmid=25278866 |doi-access=free}}</ref>

Past actions and events that transpire right before an encounter or any form of stimulation have a strong degree of influence on how sensory stimuli are processed and perceived. On a basic level, the information our senses receive is often ambiguous and incomplete. However, they are grouped together in order for us to be able to understand the physical world around us. But it is these various forms of stimulation, combined with our previous knowledge and experience that allows us to create our overall perception. For example, when engaging in conversation, we attempt to understand their message and words by not only paying attention to what we hear through our ears but also from the previous shapes we have seen our mouths make. Another example would be if we had a similar topic come up in another conversation, we would use our previous knowledge to guess the direction the conversation is headed in.<ref>{{Cite journal |last=Snyder |first=Joel |date=31 October 2015 |pmc=4628108 |title=How previous experience shapes perception in different sensory modalities |journal=Frontiers in Human Neuroscience |volume=9 |pages=594 |pmid=26582982 |doi=10.3389/fnhum.2015.00594 |doi-access=free }}</ref>

=== Effect of motivation and expectation ===
{{main|Set (psychology)}}A ''perceptual set'' (also called ''perceptual expectancy'' or simply ''set'') is a predisposition to perceive things in a certain way.<ref name="Weiten2008">{{cite book|url=https://books.google.com/books?id=sILajOhJpOsC&pg=PT193|title=Psychology: Themes and Variations|last=Weiten|first=Wayne|date=17 December 2008|publisher=Cengage Learning|isbn=978-0-495-60197-5|page=193|access-date=24 March 2011|archive-url=https://web.archive.org/web/20111109163032/http://books.google.com/books?id=sILajOhJpOsC&pg=PT193|archive-date=9 November 2011|url-status=live}}</ref> It is an example of how perception can be shaped by "top-down" processes such as drives and expectations.<ref name="CoonMitterer2008">{{cite book|url=https://books.google.com/books?id=vw20LEaJe10C&pg=PA171|title=Introduction to Psychology: Gateways to Mind and Behavior|last1=Coon|first1=Dennis|last2=Mitterer|first2=John O.|date=29 December 2008|publisher=Cengage Learning|isbn=978-0-495-59911-1|pages=171–172|access-date=24 March 2011|archive-url=https://web.archive.org/web/20111109162432/http://books.google.com/books?id=vw20LEaJe10C&pg=PA171|archive-date=9 November 2011|url-status=live}}</ref> Perceptual sets occur in all the different senses.<ref name="Sonderegger1998" /> They can be long term, such as a special sensitivity to hearing one's own name in a crowded room, or short-term, as in the ease with which hungry people notice the smell of food.<ref name="HardyHeyes1999">{{cite book|url=https://books.google.com/books?id=fjPWqXi9WQsC&pg=PA24|title=Beginning Psychology|last1=Hardy|first1=Malcolm|last2=Heyes|first2=Steve|date=2 December 1999|publisher=Oxford University Press|isbn=978-0-19-832821-6|pages=24–27|access-date=24 March 2011|archive-url=https://web.archive.org/web/20111109163023/http://books.google.com/books?id=fjPWqXi9WQsC&pg=PA24|archive-date=9 November 2011|url-status=live}}</ref> A simple demonstration of the effect involved very brief presentations of non-words such as "sael". Subjects who were told to expect words about animals read it as "seal", but others who were expecting boat-related words read it as "sail".<ref name="HardyHeyes1999" />

Sets can be created by [[motivation]] and so can result in people interpreting ambiguous figures so that they see what they want to see.<ref name="CoonMitterer2008" /> For instance, how someone perceives what unfolds during a sports game can be biased if they strongly support one of the teams.<ref name="BlockYuker2002">{{cite book|url=https://books.google.com/books?id=uNMFiMQu8BMC&pg=PA173|title=Can You Believe Your Eyes?: Over 250 Illusions and Other Visual Oddities|last1=Block|first1=J. R.|last2=Yuker|first2=Harold E.|date=1 October 2002|publisher=Robson|isbn=978-1-86105-586-6|pages=173–174|access-date=24 March 2011|archive-url=https://web.archive.org/web/20111109162334/http://books.google.com/books?id=uNMFiMQu8BMC&pg=PA173|archive-date=9 November 2011|url-status=live}}</ref> In one experiment, students were allocated to pleasant or unpleasant tasks by a computer. They were told that either a number or a letter would flash on the screen to say whether they were going to taste an orange juice drink or an unpleasant-tasting health drink. In fact, an ambiguous figure was flashed on screen, which could either be read as the letter B or the number 13. When the letters were associated with the pleasant task, subjects were more likely to perceive a letter B, and when letters were associated with the unpleasant task they tended to perceive a number 13.<ref name="Weiten2008" />

Perceptual set has been demonstrated in many social contexts. When someone has a reputation for being funny, an audience is more likely to find them amusing.<ref name="HardyHeyes1999" /> Individual's perceptual sets reflect their own personality traits. For example, people with an aggressive personality are quicker to correctly identify aggressive words or situations.<ref name="HardyHeyes1999" /> In general, perceptual speed as a mental ability is positively correlated with personality traits such as conscientiousness, emotional stability, and agreeableness suggesting its evolutionary role in preserving homeostasis.<ref>{{Cite book |last1=Stanek |first1=Kevin |url=https://umnlibraries.manifoldapp.org/projects/of-anchors-and-sails |title=Of Anchors & Sails: Personality-Ability Trait Constellations |last2=Ones |first2=Deniz |date=2023-11-20 |publisher=University of Minnesota |isbn=978-1-946135-98-8 |doi=10.24926/9781946135988}}</ref>

One classic psychological experiment showed slower reaction times and less accurate answers when a deck of [[playing cards]] reversed the color of the [[Suit (cards)|suit]] symbol for some cards (e.g. red spades and black hearts).<ref>"On the Perception of Incongruity: A Paradigm" by Jerome S. Bruner and Leo Postman. ''Journal of Personality'', 18, pp. 206-223. 1949. [http://psychclassics.yorku.ca/Bruner/Cards/ Yorku.ca] {{webarchive|url=https://web.archive.org/web/20060215174339/http://psychclassics.yorku.ca/Bruner/Cards/|date=15 February 2006}}</ref>

Philosopher [[Andy Clark]] explains that perception, although it occurs quickly, is not simply a bottom-up process (where minute details are put together to form larger wholes). Instead, our brains use what he calls ''[[predictive coding]]''. It starts with very broad constraints and expectations for the state of the world, and as expectations are met, it makes more detailed predictions (errors lead to new predictions, or ''[[learning]] processes)''. Clark says this research has various implications; not only can there be no completely "unbiased, unfiltered" perception, but this means that there is a great deal of feedback between perception and expectation (perceptual experiences often shape our beliefs, but those perceptions were based on existing beliefs).<ref>{{cite web|url=http://www.edge.org/q2011/q11_6.html|title=Predictive Coding|archive-url=https://web.archive.org/web/20131205173145/http://www.edge.org/q2011/q11_6.html|archive-date=5 December 2013|url-status=dead|access-date=24 February 2011}}</ref> Indeed, predictive coding provides an account where this type of feedback assists in stabilizing our inference-making process about the physical world, such as with perceptual constancy examples.

[[Embodied cognition]] challenges the idea of perception as internal representations resulting from a passive reception of (incomplete) sensory inputs coming from the outside world. According to O'Regan (1992), the major issue with this perspective is that it leaves the subjective character of perception unexplained.<ref>{{Cite journal |last=O'Regan |first=J. Kevin |date=1992 |title=Solving the "real" mysteries of visual perception: The world as an outside memory. |url=http://doi.apa.org/getdoi.cfm?doi=10.1037/h0084327 |journal=Canadian Journal of Psychology |language=en |volume=46 |issue=3 |pages=461–488 |doi=10.1037/h0084327 |pmid=1486554 |issn=0008-4255|url-access=subscription }}</ref> Thus, perception is understood as an active process conducted by perceiving and engaged agents (perceivers). Furthermore, perception is influenced by agents' motives and expectations, their bodily states, and the interaction between the agent's body and the environment around it.<ref>{{Cite journal |last1=O'Regan |first1=J. Kevin |last2=Noë |first2=Alva |date=2001 |title=A sensorimotor account of vision and visual consciousness |url=https://www.cambridge.org/core/product/identifier/S0140525X01000115/type/journal_article |journal=Behavioral and Brain Sciences |language=en |volume=24 |issue=5 |pages=939–973 |doi=10.1017/S0140525X01000115 |pmid=12239892 |issn=0140-525X|url-access=subscription }}</ref>

== Philosophy ==
{{main|Philosophy of perception}}
Perception is an important part of the theories of many philosophers it has been famously addressed by [[René Descartes|Rene Descartes]], [[George Berkeley]], and [[Immanuel Kant]] to name a few. In his work The Meditations Descartes begins by doubting all of his perceptions proving his existence with the famous phrase "I think therefore I am", and then works to the conclusion that perceptions are God-given.<ref>{{Citation |last=Hatfield |first=Gary |title=René Descartes |date=2023 |url=https://plato.stanford.edu/archives/win2023/entries/descartes/ |encyclopedia=The Stanford Encyclopedia of Philosophy |editor-last=Zalta |editor-first=Edward N. |access-date=2023-11-11 |edition=Winter 2023 |publisher=Metaphysics Research Lab, Stanford University |editor2-last=Nodelman |editor2-first=Uri}}</ref> George Berkely took the stance that all things that we see have a reality to them and that our perceptions were sufficient to know and understand that thing because our perceptions are capable of responding to a true reality.<ref>{{Citation |last=Downing |first=Lisa |title=George Berkeley |date=2021 |url=https://plato.stanford.edu/archives/fall2021/entries/berkeley/ |encyclopedia=The Stanford Encyclopedia of Philosophy |editor-last=Zalta |editor-first=Edward N. |access-date=2023-11-11 |edition=Fall 2021 |publisher=Metaphysics Research Lab, Stanford University}}</ref> Kant almost meets the rationalists and the empiricists half way. His theory utilizes the reality of a noumenon, the actual objects that cannot be understood, and then a phenomenon which is human understanding through the mind lens interpreting that noumenon.<ref>{{Citation |last=Rohlf |first=Michael |title=Immanuel Kant |date=2023 |url=https://plato.stanford.edu/archives/fall2023/entries/kant/ |encyclopedia=The Stanford Encyclopedia of Philosophy |editor-last=Zalta |editor-first=Edward N. |access-date=2023-11-11 |edition=Fall 2023 |publisher=Metaphysics Research Lab, Stanford University |editor2-last=Nodelman |editor2-first=Uri}}</ref>

== See also ==
{{Portal bar|Philosophy|Psychology}}
{{cmn|
* [[Action-specific perception]]
* [[Alice in Wonderland syndrome]]
* [[Apophenia]]
* [[Binding problem|Binding Problem]]
* [[Embodied cognition]]
* [[Change blindness]]
* [[Cognitive bias]]
* [[Cultural bias]]
* [[Experience model]]
* [[Feeling]]
* [[Generic views]]
* [[Ideasthesia]]
* [[Introspection]]
* [[Model-dependent realism]]
* [[Multisensory integration]]
* [[Near sets]]
* [[Neural correlates of consciousness]]
* [[Pareidolia]]
* [[Perceptual paradox]]
* [[Philosophy of perception]]
* [[Proprioception]]
* [[Qualia]]
* [[Recept]]
* [[Samjñā]], the Buddhist concept of perception
* [[Shared intentionality]]
* [[Simulated reality]]
* [[Simulation]]
* [[Transsaccadic memory]]
* [[Visual routine]]
}}

== References ==

=== Citations ===
{{reflist}}

=== Sources ===

== Bibliography ==
* Arnheim, R. (1969). ''Visual Thinking''. Berkeley: University of California Press. {{ISBN|978-0-520-24226-5}}.
* Flanagan, J. R., & [[Susan Lederman|Lederman, S. J.]] (2001). "'Neurobiology: Feeling bumps and holes. News and Views", ''Nature'', 412(6845):389–91. ([http://brain.phgy.queensu.ca/flanagan/papers/FlaLed_NAT_01.pdf PDF])
* Gibson, J. J. (1966). ''The Senses Considered as Perceptual Systems'', Houghton Mifflin.
* Gibson, J. J. (1987). ''The Ecological Approach to Visual Perception''. Lawrence Erlbaum Associates. {{ISBN|0-89859-959-8}}
* Robles-De-La-Torre, G. (2006). "The Importance of the Sense of Touch in Virtual and Real Environments". IEEE MultiMedia,13(3), Special issue on Haptic User Interfaces for Multimedia Systems, pp.&nbsp;24–30. ([https://web.archive.org/web/20140124073640/http://www.roblesdelatorre.com/gabriel/GR-IEEE-MM-2006.pdf PDF])

== External links ==
{{Sister project links|Perception}}
* [https://web.archive.org/web/20061223231555/http://www.simplypsychology.pwp.blueyonder.co.uk/perception-theories.html Theories of Perception] Several different aspects on perception
* [http://www.richardgregory.org/ Richard L Gregory] Theories of Richard. L. Gregory.
* [https://michaelbach.de/ot/ Comprehensive set of optical illusions], presented by [[Michael Bach (vision scientist)|Michael Bach]].
* [http://www.illusions.org/ Optical Illusions] Examples of well-known optical illusions.
* [https://iep.utm.edu/epis-per/ The Epistemology of Perception] Article in the ''[[Internet Encyclopedia of Philosophy]]''
* [https://iep.utm.edu/cognitive-penetrability-of-perception-and-epistemic-justification/ Cognitive Penetrability of Perception and Epistemic Justification] Article in the ''[[Internet Encyclopedia of Philosophy]]''

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