Perception

For other uses, seePerception (disambiguation).

"Percept" redirects here. For other uses, seePercept (disambiguation).

TheNecker cubeandRubin vasecan be perceived in more than one way.

Humans are able to make a very good guess on the underlying 3D shape category/identity/geometry given a silhouette of that shape.Computer visionresearchers have been able to build computational models for perception that exhibit a similar behavior and are capable of generating andreconstructing 3D shapesfrom single or multi-view depth maps or silhouettes.

Perception(fromLatinperceptio'gathering, receiving') is the organization, identification, and interpretation ofsensoryinformation in order to represent and understand the presented information or environment.All perception involves signals that go through thenervous system,which in turn result from physical or chemical stimulation of thesensory system.Visioninvolveslightstriking theretinaof theeye;smellis mediated byodor molecules;andhearinginvolvespressure waves.

Perception is not only the passive receipt of thesesignals,but it is also shaped by the recipient'slearning,memory,expectation,andattention.Sensory input is a process that transforms this low-level information to higher-level information (e.g., extracts shapes forobject recognition).The process that follows connects a person's concepts and expectations (or knowledge), restorative and selective mechanisms (such asattention) that influence perception.

Perception depends on complex functions of the nervous system, but subjectively seems mostly effortless because this processing happens outsideconsciousawareness.Since the rise ofexperimental psychologyin the 19th century,psychology's understanding of perceptionhas progressed by combining a variety of techniques.Psychophysicsquantitativelydescribes the relationships between the physical qualities of the sensory input and perception.Sensory neurosciencestudies the neural mechanisms underlying perception. Perceptual systems can also be studiedcomputationally,in terms of the information they process.Perceptual issues in philosophyinclude the extent to which sensory qualities such assound,smell orcolorexist in objective reality rather than in the mind of the perceiver.

Although people traditionally viewed the senses as passive receptors, the study ofillusionsandambiguous imageshas demonstrated that thebrain's perceptual systems actively and pre-consciously attempt to make sense of their input.There is still active debate about the extent to which perception is an active process ofhypothesistesting, analogous toscience,or whether realistic sensory information is rich enough to make this process unnecessary.

Theperceptual systemsof 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 amodular way,with different areas processing different kinds of sensory information. Some of these modules take the form ofsensory 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,tasteis strongly influenced by smell.

Process and terminology

The process of perception begins with an object in the real world, known as thedistalstimulusordistal object.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 calledtransduction.This raw pattern of neural activity is called theproximal stimulus.These neural signals are then transmitted to the brain and processed.The resulting mental re-creation of the distal stimulus is thepercept.

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.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 calledsensory modalitiesorstimulus modalities.

Bruner's model of the perceptual process

See also:Social identity theory

PsychologistJerome Brunerdeveloped 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."This model is composed of three states:

1. When people encounter an unfamiliar target, they are very open to the informationalcuescontained in the target and the situation surrounding it.
2. 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.
3. 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:

1. 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)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.
2. The Target:theobjectof 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.
3. The Situation:theenvironmentalfactors, 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 termedmultistable perception.The same stimuli, or absence of them, may result in different percepts depending on subject's culture and previous experiences.

Ambiguous figures demonstrate that a single stimulus can result in more than one percept. For example, theRubin vasecan 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

Cerebrum lobes

Vision

Main article:Visual perception

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, andintrinsically photosensitive retinal ganglion cellscaptures 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.

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 theretina,which send a signal to theretina bipolar celllayer 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.Light-altered neuron activation occurs within about 5–20 milliseconds in a rabbit retinal ganglion,although in a mouse retinal ganglion cell the initial spike takes between 40 and 240 milliseconds before the initial activation.The initial activation can be detected by anaction potentialspike, 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.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

Anatomy of the human ear. (The length of the auditory canal is exaggerated in this image.)

Brown isouter ear.

Red ismiddle ear.

Purple isinner ear.

Hearing(oraudition) is the ability to perceivesoundby detectingvibrations(i.e.,sonicdetection). Frequencies capable of being heard by humans are calledaudiooraudiblefrequencies,the range of which is typically considered to be between 20Hzand 20,000 Hz.Frequencies higher than audio are referred to asultrasonic,while frequencies below audio are referred to asinfrasonic.

Theauditory systemincludes theouter ears,which collect and filter sound waves; themiddle ear,which transforms the sound pressure (impedance matching); and theinner ear,which produces neural signals in response to the sound. By the ascendingauditory pathwaythese are led to theprimary auditory cortexwithin thetemporal lobeof the human brain, from where the auditory information then goes to thecerebral cortexfor further processing.

Sound does not usually come from a single source: in real situations, sounds from multiple sources and directions aresuperimposedas 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.

Touch

Main article:Haptic perception

The process of recognizing objects through touch is known ashaptic perception.It involves a combination ofsomatosensoryperception of patterns on the skin surface (e.g., edges, curvature, and texture) andproprioceptionof hand position and conformation. People can rapidly and accurately identify three-dimensional objects by touch.This involves exploratory procedures, such as moving the fingers over the outer surface of the object or holding the entire object in the hand.Haptic perception relies on the forces experienced during touch.

ProfessorGibsondefined the haptic system as "the sensibility of the individual to the world adjacent to his body by use of his body."Gibson and others emphasized the close link between body movement and haptic perception, where the latter isactive exploration.

The concept of haptic perception is related to the concept ofextended physiological proprioceptionaccording to which, when using a tool such as a stick, perceptual experience is transparently transferred to the end of the tool.

Taste

Main article:Taste

Taste (formally known asgustation) is the ability to perceive theflavorof substances, including, but not limited to,food.Humans receive tastes through sensory organs concentrated on the upper surface of thetongue,calledtaste budsorgustatory calyculi.The human tongue has 100 to 150 taste receptor cells on each of its roughly-ten thousand taste buds.

Traditionally, there have been four primary tastes:sweetness,bitterness,sourness,andsaltiness.The recognition and awareness ofumami,which is considered the fifth primary taste, is a relatively recent development inWestern cuisine.Other tastes can be mimicked by combining these basic tastes,all of which contribute only partially to the sensation andflavorof food in the mouth. Other factors includesmell,which is detected by theolfactory epitheliumof the nose;texture,which is detected through a variety ofmechanoreceptors,muscle nerves, etc.;and temperature, which is detected bythermoreceptors.All basic tastes are classified as eitherappetitiveoraversive,depending upon whether the things they sense are harmful or beneficial.

Smell

Main article:Olfaction

Smell is the process of absorbing molecules througholfactory organs,which are absorbed by humans through thenose.These molecules diffuse through a thick layer ofmucus;come into contact with one of thousands ofciliathat are projected from sensory neurons; and are then absorbed into a receptor (one of 347 or so).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.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 asubconsciousandinstinctivelevel.

Social

Main article:Social perception

Social perceptionis the part of perception that allows people to understand the individuals and groups of their social world. Thus, it is an element ofsocial cognition.

Though the phrase "I owe you" can be heard as three distinct words, aspectrogramreveals no clear boundaries.

Speech

Main article:Speech perception

Speech perceptionis the process by whichspoken languageis heard, interpreted and understood. Research in this field seeks to understand how human listeners recognize the sound of speech (orphonetics) 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 thetempoof the speech, as well as the physical characteristics,accent,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.

The process of perceiving speech begins at the level of the sound within the auditory signal and the process ofaudition.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.This speech information can then be used for higher-level language processes, such asword recognition.

Speech perception is not necessarily uni-directional. Higher-level language processes connected withmorphology,syntax,and/orsemanticsmay also interact with basic speech perception processes to aid in recognition of speech sounds.It may be the case that it is not necessary (maybe not even possible) for a listener to recognizephonemesbefore 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.

Faces

Main article:Face perception

Facial perceptionrefers to cognitive processes specialized in handlinghuman faces(including perceiving the identity of an individual) and facial expressions (such as emotional cues.)

Social touch

Main article:Somatosensory system § Neural processing of social touch

Thesomatosensory cortexis a part of the brain that receives and encodes sensory information from receptors of the entire body.

Affective touchis 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 theanterior cingulate cortex.Increasedblood oxygen level-dependent(BOLD) contrast imaging, identified duringfunctional magnetic resonance imaging(fMRI), shows that signals in the anterior cingulate cortex, as well as theprefrontal cortex,are highly correlated with pleasantness scores of affective touch. Inhibitorytranscranial 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.

Multi-modal perception

Multi-modal perceptionrefers to concurrent stimulation in more than one sensory modality and the effect such has on the perception of events and objects in the world.

Time (chronoception)

Main article:time perception

Chronoceptionrefers to how the passage oftimeis perceived and experienced. Although thesense of timeis not associated with a specificsensory system,the work ofpsychologistsandneuroscientistsindicates that human brains do have a system governing the perception of time,composed of a highly distributed system involving thecerebral cortex,cerebellum,andbasal ganglia.One particular component of the brain, thesuprachiasmatic nucleus,is responsible for thecircadian rhythm(commonly known as one's "internal clock" ), while other cell clusters appear to be capable of shorter-range timekeeping, known as anultradianrhythm.

One or moredopaminergic pathwaysin thecentral nervous systemappear to have a strong modulatory influence onmental chronometry,particularlyinterval timing.

Agency

Main article:Sense of agency

Sense of agencyrefers to the subjective feeling of having chosen a particular action. Some conditions, such asschizophrenia,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.

Even in non-pathologicalcases, there is a measurable difference between the making of a decision and the feeling of agency. Through methods such asthe 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, psychologistsWegnerand 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.

Familiarity

Recognition memoryis sometimes divided into two functions by neuroscientists:familiarityandrecollection.A strong sense of familiarity can occur without any recollection, for example in cases ofdeja vu.

Thetemporal lobe(specifically theperirhinal cortex) responds differently to stimuli that feel novel compared to stimuli that feel familiar.Firing ratesin the perirhinal cortex are connected with the sense of familiarity in humans and other mammals. In tests, stimulating this area at 10–15 Hz caused animals to treat even novel images as familiar, and stimulation at 30–40 Hz caused novel images to be partially treated as familiar.In particular, stimulation at 30–40 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 onlesionsin 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.

Sexual stimulation

Main article:Sexual stimulation

Sexual stimulationis anystimulus(including bodily contact) that leads to, enhances, and maintainssexual arousal,possibly even leading toorgasm.Distinct from the general sense oftouch,sexual stimulation is strongly tied tohormonal activityand chemical triggers in the body. Although sexual arousal may arise withoutphysical stimulation,achieving orgasm usually requires physical sexual stimulation (stimulation of the Krause-Fingercorpusclesfound in erogenous zones of the body.)

Other senses

Main article:Sense

Other senses enable perception ofbody balance(vestibular sense);acceleration,includinggravity;position of body parts(proprioception sense). They can also enable perception of internal senses (interoception sense), such as temperature, pain,suffocation,gag reflex,abdominal distension,fullness ofrectumandurinary bladder,and sensations felt in thethroatandlungs.

Reality

In the case of visual perception, some people can see the percept shift in theirmind's eye.Others, who are notpicture thinkers,may not necessarily perceive the 'shape-shifting' as their world changes. Thisesemplasticnature has been demonstrated by an experiment that showed thatambiguous imageshave multiple interpretations on the perceptual level.

The confusing ambiguity of perception is exploited in human technologies such ascamouflageand biologicalmimicry.For example, the wings ofEuropean peacock butterfliesbeareyespotsthat 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.

Perception is one of the oldest fields in psychology. The oldestquantitativelaws in psychology areWeber's law,which states that the smallest noticeable difference in stimulus intensity is proportional to the intensity of the reference; andFechner'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 theGestalt School of Psychology,with an emphasis on aholisticapproach.

Physiology

Main article:Sensory system

Asensory systemis a part of the nervous system responsible for processingsensoryinformation. A sensory system consists ofsensory receptors,neural pathways,and parts of the brain involved in sensory perception. Commonly recognized sensory systems are those forvision,hearing,somatic sensation(touch),tasteandolfaction(smell), as listed above. It has been suggested that the immune system is an overlooked sensory modality.In short, senses aretransducersfrom the physical world to the realm of the mind.

Thereceptive fieldis 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 eachrodorconecan see, is its receptive field.Receptive fields have been identified for thevisual system,auditory systemandsomatosensory 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.

Features

Constancy

Main article:Subjective constancy

Perceptual constancyis the ability of perceptual systems to recognize the same object from widely varying sensory inputs.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.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.One kind of perceptual constancy iscolor constancy:for example, a white piece of paper can be recognized as such under different colors and intensities of light.Another example isroughness 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.Other constancies include melody, odor, brightness and words.These constancies are not always total, but the variation in the percept is much less than the variation in the physical stimulus.The perceptual systems of the brain achieve perceptual constancy in a variety of ways, each specialized for the kind of information being processed,withphonemic restorationas a notable example from hearing.

Law of Closure. The human brain tends to perceive complete shapes even if those forms are incomplete.

Grouping (Gestalt)

Main article:Principles of grouping

Theprinciples of grouping(orGestalt laws of grouping) are a set of principles inpsychology,first proposed byGestalt 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 toperceivepatterns in the stimulus based on certain rules. These principles areorganized into six categories:

1. Proximity:the principle ofproximitystates that,all else being equal,perception tends to group stimuli that are close together as part of the same object, andstimulithat are far apart as two separate objects.
2. Similarity:the principle ofsimilaritystates 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 theirvisual textureandresemblance.
3. Closure:the principle ofclosurerefers 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.
4. Good Continuation:the principle ofgood continuationmakes 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.
5. Common Fate:the principle ofcommon fategroups 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.
6. The principle ofgood formrefers to the tendency to group together forms of similar shape, pattern,color,etc.

Later research has identified additional grouping principles.

Contrast effects

Main article: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.

"Simultaneous contrast effect"is the term used when stimuli are presented at the same time, whereassuccessive contrastapplies when stimuli are presented one after another.

The contrast effect was noted by the 17th Century philosopherJohn 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.In the early 20th Century,Wilhelm Wundtidentified contrast as a fundamental principle of perception, and since then the effect has been confirmed in many different areas.These effects shape not only visual qualities like color and brightness, but other kinds of perception, including how heavy an object feels.One experiment found that thinking of the name "Hitler" led to subjects rating a person as more hostile.Whether a piece of music is perceived as good or bad can depend on whether the music heard before it was pleasant or unpleasant.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.In the brain, brightness contrast exerts effects on both neuronalfiring ratesandneuronal synchrony.

Theories

Perception as direct perception (Gibson)

Cognitive theoriesof perception assume there is apoverty of the stimulus.This is the claim thatsensations,by themselves, are unable to provide a unique description of the world.Sensations require 'enriching', which is the role of themental model.

Theperceptual ecologyapproach was introduced by professorJames J. Gibson,who rejected the assumption of apoverty of stimulusand 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 theambient optic array.And it supposes that the visual system can explore and detect this information. The theory is information-based, not sensation-based. "He and the psychologists who work within thisparadigmdetailed how the world could be specified to a mobile, exploring organism via the lawful projection of information about the world into energy arrays."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 isdirect.

Perception-in-action

From Gibson's early work derived an ecological understanding of perception known asperception-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 callsinvariants,already exist in the real world and that all that the perception process does is home in upon them.

Theconstructivist view,held by such philosophers asErnst 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.Glasersfeld considers aninvariantas 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 orfearedby an organism will never suffer change as time goes on. Thissocial constructionisttheory thus allows for a needful evolutionary adjustment.

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 theGeneral Tau Theory.According to this theory, "tau information", or time-to-goal information is the fundamentalperceptin perception.

Evolutionary psychology

Many philosophers, such asJerry Fodor,write that the purpose of perception is knowledge. However,evolutionary psychologistshold that the primary purpose of perception is to guide action.They give the example ofdepth perception,which seems to have evolved not to aid in knowing the distances to other objects but rather to aid movement.Evolutionary psychologists argue that animals ranging fromfiddler crabsto humans use eyesight forcollision avoidance,suggesting that vision is basically for directing action, not providing knowledge.Neuropsychologistsshowed 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 ismetabolicallyexpensive. 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.

Scientists who study perception and sensation have long understood the human senses as adaptations.Depth perception consists of processing over half a dozen visual cues, each of which is based on a regularity of the physical world.Vision evolved to respond to the narrow range of electromagnetic energy that is plentiful and that does not pass through objects.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.Taste and smell respond to chemicals in the environment that were significant for fitness in the environment of evolutionary adaptedness.The sense of touch is actually many senses, including pressure, heat, cold, tickle, and pain.Pain, while unpleasant, is adaptive.An important adaptation for senses is range shifting, by which the organism becomes temporarily more or less sensitive to sensation.For example, one's eyes automatically adjust to dim or bright ambient light.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.

Evolutionary psychologists claim that perception demonstrates the principle of modularity, with specialized mechanisms handling particular perception tasks.For example, people with damage to a particular part of the brain are not able to recognize faces (prosopagnosia).Evolutionary psychology suggests that this indicates a so-called face-reading module.

Closed-loop perception

The theory ofclosed-loop perceptionproposes dynamic motor-sensory closed-loop process in which information flows through the environment and the brain in continuous loops.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.

Feature integration theory

Main article: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.

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.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 asillusory conjunctions.

The unconnected features described in the preattentive stage are combined into the objects one normally sees during the focused attention stage.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 thebinding problem).

Shared Intentionality theory

Main article:Shared intentionality

A fundamentally different approach to understanding the perception of objects relies upon the essential role ofShared intentionality.Cognitive psychologist professorMichael Tomasellohypothesized that social bonds between children and caregivers would gradually increase through the essential motive force of shared intentionality beginning from birth.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,and neurobiology.TheShared intentionalityapproach considers perception occurrence at an earlier stage of organisms' development than other theories, even before the emergence ofIntentionality.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,Intentionalityis the central issue in perception development. Nowadays, only one hypothesis attempts to explainShared intentionalityin 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 intentionalityhighlights 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,Intentionalityis a difficult problem for them since it needs the representation of the environment already categorized into objects (see alsobinding problem). The perception of objects is also problematic since it cannot appear without Intentionality. From the perspective of this hypothesis,Shared intentionalityis 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.From this account perception emerges due toShared intentionalityin the embryonic stage of development, i.e., even before birth.

Other theories of perception

• Enactivism
• The Interactive Activation and Competition Model
• Recognition-By-Components Theory(Irving Biederman)

Effects on perception

Effect of experience

Main article:Perceptual learning

With experience,organismscan 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 thehumansphere.Researchhas focused on the relation of this to other kinds oflearning,and whether it takes place in peripheralsensorysystems or in the brain's processing of sense information.Empiricalresearchshow that specific practices (such asyoga,mindfulness,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-transcendentyogapractitioners 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.

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.

Effect of motivation and expectation

Main article:Set (psychology)

Aperceptual set(also calledperceptual expectancyor simplyset) is a predisposition to perceive things in a certain way.It is an example of how perception can be shaped by "top-down" processes such as drives and expectations.Perceptual sets occur in all the different senses.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.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".

Sets can be created bymotivationand so can result in people interpreting ambiguous figures so that they see what they want to see.For instance, how someone perceives what unfolds during a sports game can be biased if they strongly support one of the teams.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.

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.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.

One classic psychological experiment showed slower reaction times and less accurate answers when a deck ofplaying cardsreversed the color of thesuitsymbol for some cards (e.g. red spades and black hearts).

PhilosopherAndy Clarkexplains 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 callspredictive 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, orlearningprocesses).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).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 cognitionchallenges 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.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.

Philosophy

Main article:Philosophy of perception

Perception is an important part of the theories of many philosophers it has been famously addressed byRene Descartes,George Berkeley,andImmanuel Kantto 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.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.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.

See also

• Action-specific perception
• Alice in Wonderland syndrome
• Apophenia
• 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

Bibliography

• Arnheim, R. (1969).Visual Thinking.Berkeley: University of California Press.ISBN978-0-520-24226-5.
• Flanagan, J. R., &Lederman, S. J.(2001). "'Neurobiology: Feeling bumps and holes. News and Views",Nature,412(6845):389–91. (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.ISBN0-89859-959-8
• 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. 24–30. (PDF)

External links

• Theories of PerceptionSeveral different aspects on perception
• Richard L GregoryTheories of Richard. L. Gregory.
• Comprehensive set of optical illusions,presented byMichael Bach.
• Optical IllusionsExamples of well-known optical illusions.
• The Epistemology of PerceptionArticle in theInternet Encyclopedia of Philosophy
• Cognitive Penetrability of Perception and Epistemic JustificationArticle in theInternet Encyclopedia of Philosophy