Humans are able to have 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 reconstructing 3D shapes from single or multi-view depth maps or silhouettes.
Perception is not only the passive receipt for of these
object recognition). The process that follows connects a person's concepts and expectations (or knowledge), 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
quantitatively describes the relationships between the physical qualities of the sensory input and perception.Sensory neuroscience studies the neural mechanisms underlying perception. Perceptual systems can also be studied computationally, in terms of the information they process. 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.
Although people traditionally viewed the senses as passive receptors, the study of illusions and ambiguous images has demonstrated that the brain'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 of hypothesis testing, analogous to science, or whether realistic sensory information is rich enough to make this process unnecessary.
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.
Process and terminology
The process of perception begins with an object in the real world, known as the
distal stimulus or distal 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 called transduction. This raw pattern of neural activity is called the proximal stimulus. These neural signals are then transmitted to the brain and processed.
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. 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 sensory modalities or stimulus modalities.
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." This model is composed of three states:
When people encounter an unfamiliar target, they are very open to the informational cues 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:
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)
. 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.
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.
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.
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.
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. 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 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. 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.
Anatomy of the human ear. (The length of the auditory canal is exaggerated in this image).
Hearing (or audition) is the ability to perceive sound by detecting vibrations (i.e., sonic detection). Frequencies capable of being heard by humans are called audio or audiblefrequencies, the range of which is typically considered to be between 20 Hz and 20,000 Hz. Frequencies higher than audio are referred to as ultrasonic, while frequencies below audio are referred to as infrasonic.
Sound does not usually come from a single source: in real situations, sounds from multiple sources and directions are 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.
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. 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.
Gibson defined 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 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.
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 buds or gustatory 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:
Smell is the process of absorbing molecules through 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 cilia that 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 a subconscious and instinctive level.
Though the phrase "I owe you" can be heard as three distinct words, a spectrogram
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
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 of
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. 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, syntax, and/or semantics may 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 recognize phonemes before recognizing higher units, such as words. In an experiment, 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.
(including perceiving the identity of an individual) and facial expressions (such as emotional cues.)
The somatosensory cortex is a part of the brain that receives and encodes sensory information from receptors of the entire body.
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 (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.
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.
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.
Even in non-pathological cases, there is a measurable difference between the making of a decision and the feeling of agency. Through methods such as 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 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.
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 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 on lesions 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.
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.
Perception is one of the oldest fields in psychology. The oldest
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 School of Psychology, with an emphasis on holistic
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 or cone can see, is its receptive field. 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.
Law of Closure. The human brain tends to perceive complete shapes even if those forms are incomplete.
Proximity: the principle of proximity states that, all else being equal, perception tends to group stimuli that are close together as part of the same object, and stimuli that are far apart as two separate objects.
Similarity: the principle of 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 visual texture and resemblance.
Closure: the principle of 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 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 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.
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.
successive contrast applies when stimuli are presented one after another.
The contrast effect was noted by the 17th Century philosopher
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.
social constructionist theory 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 the
General Tau Theory
. According to this theory, "tau information", or time-to-goal information is the fundamental percept in perception.
Many philosophers, such as Jerry Fodor, write that the purpose of perception is knowledge. However, evolutionary psychologists hold that the primary purpose of perception is to guide action. 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. Evolutionary psychologists argue that animals ranging from fiddler crabs to humans use eyesight for collision avoidance, suggesting that vision is basically for directing action, not providing knowledge.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.
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.
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 as illusory 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 the binding problem).
Empirical research show that specific practices (such as yoga, 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-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.
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.
A perceptual set (also called perceptual expectancy or simply set) 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 by motivation and 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 of
suit symbol for some cards (e.g. red spades and black hearts).
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). 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. 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.
. 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.
^Gibson, James J. (2002): "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.
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)