The philosophy of perception is concerned with the nature of perceptual experience and the status of perceptual data, in particular how they relate to beliefs about, or knowledge of, the world. Any explicit account of perception requires a commitment to one of a variety of ontological or metaphysical views. Philosophers distinguish internalist accounts, which assume that perceptions of objects, and knowledge or beliefs about them, are aspects of an individual's mind, and externalist accounts, which state that they constitute real aspects of the world external to the individual. The position of naïve realism—the 'everyday' impression of physical objects constituting what is perceived—is to some extent contradicted by the occurrence of perceptual illusions and hallucinations and the relativity of perceptual experience as well as certain insights in science. Realist conceptions include phenomenalism and direct and indirect realism. Anti-realist conceptions include idealism and skepticism. Recent philosophical work have expanded on the philosophical features of perception by going beyond the single paradigm of vision.
Perception is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous system, which in turn result from physical or chemical stimulation of the sensory system. Vision involves light striking the retina of the eye; smell is mediated by odor molecules; and hearing involves pressure waves.
A hallucination is a perception in the absence of an external stimulus that has the qualities of a real perception. Hallucinations are vivid, substantial, and are perceived to be located in external objective space. Hallucination is a combination of two conscious states of brain wakefulness and REM sleep. They are distinguishable from several related phenomena, such as dreaming, which does not involve wakefulness; pseudohallucination, which does not mimic real perception, and is accurately perceived as unreal; illusion, which involves distorted or misinterpreted real perception; and mental imagery, which does not mimic real perception, and is under voluntary control. Hallucinations also differ from "delusional perceptions", in which a correctly sensed and interpreted stimulus is given some additional significance.
In visual perception, an optical illusion is an illusion caused by the visual system and characterized by a visual percept that arguably appears to differ from reality. Illusions come in a wide variety; their categorization is difficult because the underlying cause is often not clear but a classification proposed by Richard Gregory is useful as an orientation. According to that, there are three main classes: physical, physiological, and cognitive illusions, and in each class there are four kinds: Ambiguities, distortions, paradoxes, and fictions. A classical example for a physical distortion would be the apparent bending of a stick half immerged in water; an example for a physiological paradox is the motion aftereffect. An example for a physiological fiction is an afterimage. Three typical cognitive distortions are the Ponzo, Poggendorff, and Müller-Lyer illusion. Physical illusions are caused by the physical environment, e.g. by the optical properties of water. Physiological illusions arise in the eye or the visual pathway, e.g. from the effects of excessive stimulation of a specific receptor type. Cognitive visual illusions are the result of unconscious inferences and are perhaps those most widely known.
A tactile illusion is an illusion that affects the sense of touch. Some tactile illusions require active touch, whereas others can be evoked passively. In recent years, a growing interest among perceptual researchers has led to the discovery of new tactile illusions and to the celebration of tactile illusions in the popular science press. Some tactile illusions are analogous to visual and auditory illusions, suggesting that these sensory systems may process information in similar ways; other tactile illusions don't have obvious visual or auditory analogs.
Stimulus modality, also called sensory modality, is one aspect of a stimulus or what is perceived after a stimulus. For example, the temperature modality is registered after heat or cold stimulate a receptor. Some sensory modalities include: light, sound, temperature, taste, pressure, and smell. The type and location of the sensory receptor activated by the stimulus plays the primary role in coding the sensation. All sensory modalities work together to heighten stimuli sensation when necessary.
Multisensory integration, also known as multimodal integration, is the study of how information from the different sensory modalities may be integrated by the nervous system. A coherent representation of objects combining modalities enables animals to have meaningful perceptual experiences. Indeed, multisensory integration is central to adaptive behavior because it allows animals to perceive a world of coherent perceptual entities. Multisensory integration also deals with how different sensory modalities interact with one another and alter each other's processing.
Sensory substitution is a change of the characteristics of one sensory modality into stimuli of another sensory modality.
Sensory processing is the process that organizes and distinguishes sensation from one's own body and the environment, thus making it possible to use the body effectively within the environment. Specifically, it deals with how the brain processes multiple sensory modality inputs, such as proprioception, vision, auditory system, tactile, olfactory, vestibular system, interoception, and taste into usable functional outputs.
Troxler's fading, also called Troxler fading or the Troxler effect, is an optical illusion affecting visual perception. When one fixates on a particular point for even a short period of time, an unchanging stimulus away from the fixation point will fade away and disappear. Research suggests that at least some portion of the perceptual phenomena associated with Troxler's fading occurs in the brain.
In neurobiology, lateral inhibition is the capacity of an excited neuron to reduce the activity of its neighbors. Lateral inhibition disables the spreading of action potentials from excited neurons to neighboring neurons in the lateral direction. This creates a contrast in stimulation that allows increased sensory perception. It is also referred to as lateral antagonism and occurs primarily in visual processes, but also in tactile, auditory, and even olfactory processing. Cells that utilize lateral inhibition appear primarily in the cerebral cortex and thalamus and make up lateral inhibitory networks (LINs). Artificial lateral inhibition has been incorporated into artificial sensory systems, such as vision chips, hearing systems, and optical mice. An often under-appreciated point is that although lateral inhibition is visualised in a spatial sense, it is also thought to exist in what is known as "lateral inhibition across abstract dimensions." This refers to lateral inhibition between neurons that are not adjacent in a spatial sense, but in terms of modality of stimulus. This phenomenon is thought to aid in colour discrimination.
A sensory cue is a statistic or signal that can be extracted from the sensory input by a perceiver, that indicates the state of some property of the world that the perceiver is interested in perceiving.
The cutaneous rabbit illusion is a tactile illusion evoked by tapping two or more separate regions of the skin in rapid succession. The illusion is most readily evoked on regions of the body surface that have relatively poor spatial acuity, such as the forearm. A rapid sequence of taps delivered first near the wrist and then near the elbow creates the sensation of sequential taps hopping up the arm from the wrist towards the elbow, although no physical stimulus was applied between the two actual stimulus locations. Similarly, stimuli delivered first near the elbow then near the wrist evoke the illusory perception of taps hopping from elbow towards wrist. The illusion was discovered by Frank Geldard and Carl Sherrick of Princeton University, in the early 1970s, and further characterized by Geldard (1982) and in many subsequent studies. Geldard and Sherrick likened the perception to that of a rabbit hopping along the skin, giving the phenomenon its name. While the rabbit illusion has been most extensively studied in the tactile domain, analogous sensory saltation illusions have been observed in audition and vision. The word "saltation" refers to the leaping or jumping nature of the percept.
Extinction is a neurological disorder that impairs the ability to perceive multiple stimuli of the same type simultaneously. Extinction is usually caused by damage resulting in lesions on one side of the brain. Those who are affected by extinction have a lack of awareness in the contralesional side of space and a loss of exploratory search and other actions normally directed toward that side.
A sense is a biological system used by an organism for sensation, the process of gathering information about the surroundings through the detection of stimuli. Although, in some cultures, five human senses were traditionally identified as such, many more are now recognized. Senses used by non-human organisms are even greater in variety and number. During sensation, sense organs collect various stimuli for transduction, meaning transformation into a form that can be understood by the brain. Sensation and perception are fundamental to nearly every aspect of an organism's cognition, behavior and thought.
In psychology, visual capture is the dominance of vision over other sense modalities in creating a percept. In this process, the visual senses influence the other parts of the somatosensory system, to result in a perceived environment that is not congruent with the actual stimuli. Through this phenomenon, the visual system is able to disregard what other information a different sensory system is conveying, and provide a logical explanation for whatever output the environment provides. Visual capture allows one to interpret the location of sound as well as the sensation of touch without actually relying on those stimuli but rather creating an output that allows the individual to perceive a coherent environment.
Chronostasis is a type of temporal illusion in which the first impression following the introduction of a new event or task-demand to the brain can appear to be extended in time. For example, chronostasis temporarily occurs when fixating on a target stimulus, immediately following a saccade. This elicits an overestimation in the temporal duration for which that target stimulus was perceived. This effect can extend apparent durations by up to half a second and is consistent with the idea that the visual system models events prior to perception.
Geometrical–optical are visual illusions, also optical illusions, in which the geometrical properties of what is seen differ from those of the corresponding objects in the visual field.
Multistable auditory perception is a cognitive phenomenon in which certain auditory stimuli can be perceived in multiple ways. While multistable perception has been most commonly studied in the visual domain, it also has been observed in the auditory and olfactory modalities. In the olfactory domain, different scents are piped to the two nostrils, while in the auditory domain, researchers often examine the effects of binaural sequences of pure tones. Generally speaking, multistable perception has three main characteristics: exclusivity, implying that the multiple perceptions cannot simultaneously occur; randomness, indicating that the duration of perceptual phases follows a random law, and inevitability, meaning that subjects are unable to completely block out one percept indefinitely.
Interindividual differences in perception describes the effect that differences in brain structure or factors such as culture, upbringing and environment have on the perception of humans. Interindividual variability is usually regarded as a source of noise for research. However, in recent years, it has become an interesting source to study sensory mechanisms and understand human behavior. With the help of modern neuroimaging methods such as fMRI and EEG, individual differences in perception could be related to the underlying brain mechanisms. This has helped to explain differences in behavior and cognition across the population. Common methods include studying the perception of illusions, as they can effectively demonstrate how different aspects such as culture, genetics and the environment can influence human behavior.
