The philosophy of perception is concerned with the nature of perceptual experience

Perception

Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...

 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

Metaphysical

Metaphysical may refer to:*Metaphysics, a branch of philosophy dealing with aspects of existence and the theory of knowledge*The supernatural...

 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

Externalism

Externalism is a group of positions in the philosophy of mind which hold that the mind is not only the result of what is going on inside the nervous system but also of what either occur or exist outside the subject. It is often contrasted with internalism which holds that the mind emerges out of...

 accounts, which state that they constitute real aspects of the world external to the individual. The position of naïve realism

Naïve realism

Naïve realism, also known as direct realism or common sense realism, is a philosophy of mind rooted in a common sense theory of perception that claims that the senses provide us with direct awareness of the external world...

 — 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

Philosophical realism

Contemporary philosophical realism is the belief that our reality, or some aspect of it, is ontologically independent of our conceptual schemes, linguistic practices, beliefs, etc....

 conceptions include phenomenalism

Phenomenalism

Phenomenalism is the view that physical objects do not exist as things in themselves but only as perceptual phenomena or sensory stimuli situated in time and in space...

 and direct and indirect realism

Direct and indirect realism

The question of direct or "naïve" realism, as opposed to indirect or "representational" realism, arises in the philosophy of perception and of mind out of the debate over the nature of conscious experience; the epistemological question of whether the world we see around us is the real world itself...

. Anti-realist

Anti-realism

In analytic philosophy, the term anti-realism is used to describe any position involving either the denial of an objective reality of entities of a certain type or the denial that verification-transcendent statements about a type of entity are either true or false...

 conceptions include idealism

Idealism

In philosophy, idealism is the family of views which assert that reality, or reality as we can know it, is fundamentally mental, mentally constructed, or otherwise immaterial. Epistemologically, idealism manifests as a skepticism about the possibility of knowing any mind-independent thing...

 and skepticism

Philosophical skepticism

Philosophical skepticism is both a philosophical school of thought and a method that crosses disciplines and cultures. Many skeptics critically examine the meaning systems of their times, and this examination often results in a position of ambiguity or doubt...

.

Categories of perception

We may categorize perception as internal or external.

• Internal perception (proprioception
  Proprioception
  Proprioception , from Latin proprius, meaning "one's own" and perception, is the sense of the relative position of neighbouring parts of the body and strength of effort being employed in movement...
  
  ) tells us what is going on in our bodies; where our limbs are, whether we are sitting or standing, whether we are hungry or tired and so forth.

• External or Sensory perception (exteroception), tells us about the world outside our bodies. Using our senses of sight, hearing, touch, smell, and taste, we perceive colors, sounds, textures, etc. of the world at large. There is a growing body of knowledge of the mechanics of sensory processes in cognitive psychology
  Cognitive psychology
  Cognitive psychology is a subdiscipline of psychology exploring internal mental processes.It is the study of how people perceive, remember, think, speak, and solve problems.Cognitive psychology differs from previous psychological approaches in two key ways....
  
  .

The philosophy of perception is mainly concerned with exteroception.

Scientific accounts of perception

An object at some distance from an observer will reflect light from the sun in all directions, some of which will fall upon the corneae of the eye

Human eye

The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...

s where it will be focussed upon each retina

Retina

The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

, forming an image. The disparity between the electrical output of these two slightly different images is resolved either at the level of the lateral geniculate nucleus or in a part of the visual cortex

Visual cortex

The visual cortex of the brain is the part of the cerebral cortex responsible for processing visual information. It is located in the occipital lobe, in the back of the brain....

 called 'V1'. The resolved data is further processed in the visual cortex where some areas have specialised functions, for instance area V5 is involved in the modelling of motion and V4 in adding colour. The resulting single image that subjects report as their experience is called a 'percept'. Studies involving rapidly changing scenes show the percept derives from numerous processes that involve time delays . Recent fMRI studies show that dreams, imaginings and perceptions of things such as faces are accompanied by activity in many of the same areas of brain as are involved with physical sight. Imagery that originates from the senses and internally generated imagery may have a shared ontology

Ontology

Ontology is the philosophical study of the nature of being, existence or reality as such, as well as the basic categories of being and their relations...

 at higher levels of cortical processing.

Sound

Sound

Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...

 is pressure waves sensed by the cochlea

Cochlea

The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....

 in the ear. Data from the eyes and ears is combined to form a 'bound' percept. The problem of how this is produced, known as the binding problem

Binding problem

The binding problem is one of a number of terms at the interface between neuroscience and philosophy which suffer from being used in several different ways, often in a context that does not explicitly indicate which way the term is being used. Of the many possible usages, two common versions may be...

, is the subject of considerable study.

Perception is a cognitive process in which information processing

Information processing

Information processing is the change of information in any manner detectable by an observer. As such, it is a process which describes everything which happens in the universe, from the falling of a rock to the printing of a text file from a digital computer system...

 is used to transfer information into the mind where it is related to other information. Some psychologists propose that this processing gives rise to particular mental states (cognitivism

Cognitivism (psychology)

In psychology, cognitivism is a theoretical framework for understanding the mind that came into usage in the 1950s. The movement was a response to behaviorism, which cognitivists said neglected to explain cognition...

) whilst others envisage a direct path back into the external world in the form of action (radical behaviourism). Behaviourists such as John B. Watson

John B. Watson

John Broadus Watson was an American psychologist who established the psychological school of behaviorism. Watson promoted a change in psychology through his address Psychology as the Behaviorist Views it which was given at Columbia University in 1913...

 and B.F. Skinner have proposed that perception acts largely as a process between a stimulus and a response but have noted that Gilbert Ryle

Gilbert Ryle

Gilbert Ryle , was a British philosopher, a representative of the generation of British ordinary language philosophers that shared Wittgenstein's approach to philosophical problems, and is principally known for his critique of Cartesian dualism, for which he coined the phrase "the ghost in the...

's "ghost in the machine

Ghost in the machine

The "ghost in the machine" is the British philosopher Gilbert Ryle's description of René Descartes' mind-body dualism. The phrase was introduced in Ryle's book The Concept of Mind to highlight the perceived absurdity of dualist systems like Descartes' where mental activity carries on in parallel...

 of the brain" still seems to exist. "The objection to inner states is not that they do not exist, but that they are not relevant in a functional analysis". This view, in which experience is thought to be an incidental by-product of information processing, is known as epiphenomenalism

Epiphenomenalism

In philosophy of mind, epiphenomenalism, also known as Type-E Dualism, is a view that "mental" states do not have any influence on "physical" states.-Background:...

.

Philosophical accounts of perception

Important philosophical problems derive from the epistemology of perception — how we can gain knowledge via perception - such as the question of the nature of qualia

Qualia

Qualia , singular "quale" , from a Latin word meaning for "what sort" or "what kind," is a term used in philosophy to refer to subjective conscious experiences as 'raw feels'. Examples of qualia are the pain of a headache, the taste of wine, the experience of taking a recreational drug, or the...

. Within the biological study of perception naive realism is unusable. However, outside biology modified forms of naive realism are defended. Thomas Reid

Thomas Reid

The Reverend Thomas Reid FRSE , was a religiously trained Scottish philosopher, and a contemporary of David Hume, was the founder of the Scottish School of Common Sense, and played an integral role in the Scottish Enlightenment...

, the eighteenth-century founder of the Scottish School of Common Sense, realised that sensation was composed of a set of data transfers but declared that there is still a direct connection between perception and the world. This idea, called direct realism, has again become popular in recent years with the rise of postmodernism

Postmodernism

Postmodernism is a philosophical movement evolved in reaction to modernism, the tendency in contemporary culture to accept only objective truth and to be inherently suspicious towards a global cultural narrative or meta-narrative. Postmodernist thought is an intentional departure from the...

.

The succession of data transfers involved in perception suggests that sense data

Sense data

In the philosophy of perception, the theory of sense data was a popular view held the early 20th century by philosophers such as Bertrand Russell, C. D. Broad, H. H. Price, A.J. Ayer and G.E. Moore, among others. Sense data are supposedly mind-dependent objects whose existence and properties are...

 are somehow available to a perceiving subject that is the substrate of the percept. Indirect realism, the view held by John Locke

John Locke

John Locke FRS , widely known as the Father of Liberalism, was an English philosopher and physician regarded as one of the most influential of Enlightenment thinkers. Considered one of the first of the British empiricists, following the tradition of Francis Bacon, he is equally important to social...

 and Nicolas Malebranche

Nicolas Malebranche

Nicolas Malebranche ; was a French Oratorian and rationalist philosopher. In his works, he sought to synthesize the thought of St. Augustine and Descartes, in order to demonstrate the active role of God in every aspect of the world...

, proposes that we can only be aware of mental representation

Mental representation

A representation, in philosophy of mind, cognitive psychology, neuroscience, and cognitive science, is a hypothetical internal cognitive symbol that represents external reality, or else a mental process that makes use of such a symbol; "a formal system for making explicit certain entities or types...

s of objects. however this may imply an infinite regress (a perceiver within a perceiver within a perceiver...), though a finite regress is perfectly possible. It also assumes that perception is entirely due to data transfer and information processing, an argument that can be avoided by proposing that the percept does not depend wholly upon the transfer and rearrangement of data. This still involves basic ontological issues of the sort raised by Leibniz Locke, Hume

David Hume

David Hume was a Scottish philosopher, historian, economist, and essayist, known especially for his philosophical empiricism and skepticism. He was one of the most important figures in the history of Western philosophy and the Scottish Enlightenment...

, Whitehead

Alfred North Whitehead

Alfred North Whitehead, OM FRS was an English mathematician who became a philosopher. He wrote on algebra, logic, foundations of mathematics, philosophy of science, physics, metaphysics, and education...

 and others, which remain outstanding particularly in relation to the binding problem

Binding problem

The binding problem is one of a number of terms at the interface between neuroscience and philosophy which suffer from being used in several different ways, often in a context that does not explicitly indicate which way the term is being used. Of the many possible usages, two common versions may be...

, the question of how different perceptions (e.g. color and contour in vision) are "bound" to the same object when they are processed by separate areas of the brain.

Indirect realism provides an account of issues such as qualia

Qualia

Qualia , singular "quale" , from a Latin word meaning for "what sort" or "what kind," is a term used in philosophy to refer to subjective conscious experiences as 'raw feels'. Examples of qualia are the pain of a headache, the taste of wine, the experience of taking a recreational drug, or the...

, dreams, imaginings, hallucinations, illusions, the resolution of binocular rivalry

Binocular rivalry

Binocular rivalry is a phenomenon of visual perception in which perception alternates between different images presented to each eye.When one image is presented to one eye and a very different image is presented to the other, instead of the two images being seen superimposed, one image is seen for...

, the resolution of multistable perception

Multistable perception

Multistable perceptual phenomena are a form of perceptual phenomena in which there are unpredictable sequences of spontaneous subjective changes...

, the modelling of motion that allows us to watch TV, the sensations that result from direct brain stimulation, the update of the mental image by saccades of the eyes and the referral of events backwards in time. Direct realists must either argue that these experiences do not occur or else refuse to define them as perceptions.

Idealism holds that reality is limited to mental qualities while skepticism challenges our ability to know anything outside our minds. One of the most influential proponents of idealism was George Berkeley

George Berkeley

George Berkeley , also known as Bishop Berkeley , was an Irish philosopher whose primary achievement was the advancement of a theory he called "immaterialism"...

 who maintained that everything was mind or dependent upon mind. Berkeley's idealism has two main strands, phenomenalism

Phenomenalism

Phenomenalism is the view that physical objects do not exist as things in themselves but only as perceptual phenomena or sensory stimuli situated in time and in space...

 in which physical events are viewed as a special kind of mental event and subjective idealism

Subjective idealism

Subjective idealism, or empirical idealism, is the monistic metaphysical doctrine that only minds and mental contents exist. It entails and is generally identified or associated with immaterialism, the doctrine that physical things do not exist...

. David Hume

David Hume

David Hume was a Scottish philosopher, historian, economist, and essayist, known especially for his philosophical empiricism and skepticism. He was one of the most important figures in the history of Western philosophy and the Scottish Enlightenment...

 is probably the most influential proponent of skepticism.

A third theory of perception, enactivism, attempts to find a middle path between realist and anti-realist theories, positing that cognition

Cognition

In science, cognition refers to mental processes. These processes include attention, remembering, producing and understanding language, solving problems, and making decisions. Cognition is studied in various disciplines such as psychology, philosophy, linguistics, and computer science...

 arises as a result of the dynamic interplay between an organism's sensory-motor capabilities and its environment. Instead of seeing perception as a passive process determined entirely by the features of an independently existing world, enactivism suggests that organism and environment are structurally coupled and co-determining. The theory was first formalized by Francisco Varela, Evan Thompson, and Eleanor Rosch in "The Embodied Mind".

Spatial representation

An aspect of perception that is common to both realists and anti-realists is the idea of mental or perceptual space

Visual space

Visual space is the perceptual space housing the visual world being experienced by an aware observer; it is the subjective counterpart of the space of physical objects before an observer's eyes.-Space of Physical Objects:...

. David Hume

David Hume

David Hume was a Scottish philosopher, historian, economist, and essayist, known especially for his philosophical empiricism and skepticism. He was one of the most important figures in the history of Western philosophy and the Scottish Enlightenment...

 concluded that things appear extended because they have attributes of colour and solidity. A popular modern philosophical view is that the brain cannot contain images so our sense of space must be due to the actual space occupied by physical things. However, as René Descartes noticed, perceptual space has a projective geometry, things within it appear as if they are viewed from a point. The phenomenon of perspective

Perspective

- Literally, in visual topics :* Perspective , the way in which objects appear to the eye.* Perspective , representing the effects of visual perspective in graphic arts- Metaphorically, in relation to cognitive topics :...

 was closely studied by artists and architects in the Renaissance, who relied mainly on the 11th century polymath, Alhazen (Ibn al-Haytham), who affirmed the visibility of perceptual space in geometric structuring projections. Mathematicians now know of many types of projective geometry such as complex Minkowski space

Minkowski space

In physics and mathematics, Minkowski space or Minkowski spacetime is the mathematical setting in which Einstein's theory of special relativity is most conveniently formulated...

 that might describe the layout of things in perception (see Peters (2000)) and it has also emerged that parts of the brain contain patterns of electrical activity that correspond closely to the layout of the retinal image (this is known as retinotopy

Retinotopy

Retinotopy describes the spatial organization of the neuronal responses to visual stimuli. In many locations within the brain, adjacent neurons have receptive fields that include slightly different, but overlapping portions of the visual field. The position of the center of these receptive fields...

). How or whether these become conscious experience is still unknown(see McGinn (1995)).

See also

• Argument from illusion
  Argument from illusion
  The argument from illusion is an argument for the existence of sense-data. It is posed as a criticism of direct realism. Naturally occurring illusions best illustrate the argument's points, a notable example concerning a stick: I have a stick, which appears to me to be straight, but when I hold it...
  
  
• Arthur Schopenhauer
  Arthur Schopenhauer
  Arthur Schopenhauer was a German philosopher known for his pessimism and philosophical clarity. At age 25, he published his doctoral dissertation, On the Fourfold Root of the Principle of Sufficient Reason, which examined the four separate manifestations of reason in the phenomenal...
  
  
• Āyatana (Sense Bases in Theravada Buddhism)
• Binding problem
  Binding problem
  The binding problem is one of a number of terms at the interface between neuroscience and philosophy which suffer from being used in several different ways, often in a context that does not explicitly indicate which way the term is being used. Of the many possible usages, two common versions may be...
  
  
• Consciousness
  Consciousness
  Consciousness is a term that refers to the relationship between the mind and the world with which it interacts. It has been defined as: subjectivity, awareness, the ability to experience or to feel, wakefulness, having a sense of selfhood, and the executive control system of the mind...
  
  
• Direct Realism
• Epistemology
• George Berkeley
  George Berkeley
  George Berkeley , also known as Bishop Berkeley , was an Irish philosopher whose primary achievement was the advancement of a theory he called "immaterialism"...
  
  
• Hallucinations in the sane
  Hallucinations in the sane
  A hallucination may occur in a person in a state of good mental and physical health, even in the apparent absence of a transient trigger factor such as fatigue, intoxication or sensory deprivation....
  
  
• Immanuel Kant
  Immanuel Kant
  Immanuel Kant was a German philosopher from Königsberg , researching, lecturing and writing on philosophy and anthropology at the end of the 18th Century Enlightenment....
  
  
• Idealism
  Idealism
  In philosophy, idealism is the family of views which assert that reality, or reality as we can know it, is fundamentally mental, mentally constructed, or otherwise immaterial. Epistemologically, idealism manifests as a skepticism about the possibility of knowing any mind-independent thing...
  
  
• Indirect Realism
• Map-territory relation
• Maurice Merleau-Ponty
  Maurice Merleau-Ponty
  Maurice Merleau-Ponty was a French phenomenological philosopher, strongly influenced by Karl Marx, Edmund Husserl and Martin Heidegger in addition to being closely associated with Jean-Paul Sartre and Simone de Beauvoir...
  
  
• Mind's eye
  Mind's eye
  The phrase "mind's eye" refers to the human ability for visualization, i.e., for the experiencing of visual mental imagery; in other words, one's ability to "see" things with the mind.- Physical basis :...
  
  
• Multistable perception
  Multistable perception
  Multistable perceptual phenomena are a form of perceptual phenomena in which there are unpredictable sequences of spontaneous subjective changes...
  
  
• Perception
  Perception
  Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
  
  
• Philosophical realism
  Philosophical realism
  Contemporary philosophical realism is the belief that our reality, or some aspect of it, is ontologically independent of our conceptual schemes, linguistic practices, beliefs, etc....
  
  
• Roderick Chisholm
  Roderick Chisholm
  Roderick M. Chisholm was an American philosopher known for his work on epistemology, metaphysics, free will, and the philosophy of perception. He received his Ph.D. at Harvard University under Clarence Irving Lewis and Donald C. Williams, and taught at Brown University...
  
  
• Sensorium
  Sensorium
  The term sensorium refers to the sum of an organism's perception, the "seat of sensation" where it experiences and interprets the environments within which it lives. The term originally enters English from the Late Latin in the mid-17th century, from the stem sens-...
  
  
• Subjective character of experience
  Subjective character of experience
  The subjective character of experience is a term in psychology and the philosophy of mind denoting that all subjective phenomena are associated with a single point of view...
  
  
• Thomas Reid
  Thomas Reid
  The Reverend Thomas Reid FRSE , was a religiously trained Scottish philosopher, and a contemporary of David Hume, was the founder of the Scottish School of Common Sense, and played an integral role in the Scottish Enlightenment...
  
  
• Transcendental idealism
  Transcendental idealism
  Transcendental idealism is a doctrine founded by German philosopher Immanuel Kant in the eighteenth century. Kant's doctrine maintains that human experience of things is similar to the way they appear to us — implying a fundamentally subject-based component, rather than being an activity that...
  
  
• Visual perception
  Visual perception
  Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
  
  
• Visual space
  Visual space
  Visual space is the perceptual space housing the visual world being experienced by an aware observer; it is the subjective counterpart of the space of physical objects before an observer's eyes.-Space of Physical Objects:...
  
  

Other references and further reading

• Chalmers DJ. (1995) Facing up to the hard problem of consciousness. Journal of Consciousness Studies 2, 3, 200-219.
• Wikibooks: Consciousness Studies
• BonJour, Laurence (2001). "Epistemological Problems of Perception," The Stanford Encyclopedia of Philosophy, Edward Zalta (ed.). Online text
• Burge, Tyler (1991). "Vision and Intentional Content," in E. LePore and R. Van Gulick (eds.) John Searle and his Critics, Oxford: Blackwell.
• Crane, Tim (2005). "The Problem of Perception," The Stanford Encyclopedia of Philosophy, Edward Zalta (ed.). Online text
• Descartes, Rene (1641). Meditations on First Philosophy. Online text
• Dretske, Fred (1981). Knowledge and the Flow of Information, Oxford: Blackwell.
• Evans, Gareth (1982). The Varieties of Reference, Oxford: Clarendon Press.
• Flynn, Bernard (2004). "Maurice Merleau-Ponty," The Stanford Encyclopedia of Philosophy, Edward Zalta (ed.). Online text
• Hume, David (1739–40). A Treatise of Human Nature: Being An Attempt to Introduce the Experimental Method of Reasoning Into Moral Subjects. Online text
• Kant, Immanuel (1781). Critique of Pure Reason. Norman Kemp Smith (trans.) with preface by Howard Caygill, Palgrave Macmillan. Online text
• Lacewing, Michael (unpublished). "Phenomenalism." Online PDF
• Locke, John (1689). An Essay Concerning Human Understanding. Online text
• McCreery, Charles (2006). "Perception and Hallucination: the Case for Continuity." Philosophical Paper No. 2006-1. Oxford: Oxford Forum. Online PDF
• McDowell, John, (1982). "Criteria, Defeasibility, and Knowledge," Proceedings of the British Academy, pp. 455–79.
• McDowell, John, (1994). Mind and World, Cambridge, Mass.: Harvard University Press.
• McGinn, Colin (1995). "Consciousness and Space," In Conscious Experience, Thomas Metzinger (ed.), Imprint Academic. Online text
• Mead, George Herbert (1938). "Mediate Factors in Perception," Essay 8 in The Philosophy of the Act, Charles W. Morris with John M. Brewster, Albert M. Dunham and David Miller (eds.), Chicago: University of Chicago, pp. 125–139. Online text
• Moutoussis, K. and Zeki, S. (1997). "A Direct Demonstration of Perceptual Asynchrony in Vision," Proceedings of the Royal Society of London, Series B: Biological Sciences, 264, pp. 393–399.
• Noe, Alva/Thompson, Evan T.: Vision and Mind: Selected Readings in the Philosophy of Perception, Cambridge: MIT Press, 2002.
• Peacocke, Christopher (1983). Sense and Content, Oxford: Oxford University Press.
• Peters, G. (2000). "Theories of Three-Dimensional Object Perception - A Survey," Recent Research Developments in Pattern Recognition, Transworld Research Network. Online text
• Putnam, Hilary (1999). The Threefold Cord, New York: Columbia University Press.
• Read, Czerne (unpublished). "Dreaming in Color." Online text
• Russell, Bertrand (1912). The Problems of Philosophy, London: Williams and Norgate; New York: Henry Holt and Company. Online text
• Shoemaker, Sydney (1990). "Qualities and Qualia: What's in the Mind?" Philosophy and Phenomenological Research 50, Supplement, pp. 109–31.
• Siegel, Susanna (2005). "The Contents of Perception," The Stanford Encyclopedia of Philosophy, Edward Zalta (ed.). Online text
• Tong, Frank (2003). "Primary Visual Cortex and Visual Awareness," Nature Reviews, Neuroscience, Vol 4, 219. Online text
• Tye, Michael (2000). Consciousness, Color and Content, Cambridge, MA: MIT Press.
• Infoactivity Genesis of perception investigation

External links

• The Problem of Perception at the Stanford Encyclopedia of Philosophy.
• Epistemological Problems of Perception at the Stanford Encyclopedia of Philosophy.