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perception: Definition, Synonyms and Much More from Answers.com

️Wed Jul 01 2015

Those subjective experiences of objects or events that ordinarily result from stimulation of the receptor organs of the body. This stimulation is transformed or encoded into neural activity (by specialized receptor mechanisms) and is relayed to more central regions of the nervous system where further neural processing occurs. Most likely, it is the final neural processing in the brain that underlies or causes perceptual experience, and so perceptionlike experiences can sometimes occur without external stimulation of the receptor organs, as in dreams.

In contemporary psychology, interest generally focuses on perception or the apprehension of objects or events, rather than simply on sensation or sensory process. While no sharp line of demarcation between these topics exists, it is fair to say that sensory qualities are generally explicable on the basis of mechanisms within the receptor organ, whereas object and event perception entails higher-level activity of the brain. See also Hearing (human); Sensation; Vision.

Since objects or events are not experienced only through vision, the term perception obviously applies to other sense modalities as well. Certainly things and their movement may be experienced through the sense of touch. Such experiences derive from receptors in the skin (tactile perception), but more importantly, from the positioning of the fingers with respect to one another when an object is grasped, the latter information arising from receptors in the muscles and joints (haptic or tactual perception). The position of the parts of the body are also perceived with respect to one another whether they are stationary (proprioception) or in motion (kinesthesis), and the position of the body is experienced with respect to the environment through receptors sensitive to gravity such as those in the vestibular apparatus in the inner ear. Auditory perception yields recognition of the location of sound sources and of structures such as melodies and speech. Other sense modalities such as taste (gustation), smell (olfaction), pain, and temperature provide sensory qualities but not perceptual structures as do vision, audition, and touch, and thus are usually dealt with as sensory processes. See also Olfaction; Pain; Proprioception.

Constancy

By and large, these perceptual properties of objects remain remarkably constant despite variations in distance, slant, and retinal locus caused by movements of the observer. This fact, referred to as perceptual constancy, is perhaps the hallmark of perception and more than any other, serves to characterize the field of perception.

Examples of perceptual constancy are: size (except at very great distances, an object appears the same size whether seen nearby or far away, although the size of its image on the retina can be very different); shape (a circle seen from the side is perceived as a circle, although it appears as an ellipse on the retina); orientation (objects appear to keep the same orientation in space, independently of the orientation of the observer's head); and position (a fixed object remains perceived as stationary even when its image on the retina moves because of eye or head movements).

Motion perception

Perceived movement cannot simply be explained by the motion of an object's retinal image since image motion caused by observer or eye movement does not lead to perceived object movement. Moreover, an object tracked by smooth-pursuit eye movements will appear to move, although in that case there is essentially no motion of the object's image over the retina. Similarly, an afterimage will appear to move during eye movement even in a completely darkened room. Where ordinarily the movement of the retinal image caused by the moving eye is computed to signify “no object motion,” thus yielding position constancy (since the image motion and eye motion are equal in magnitude), the same computational rule must signify “object motion” in the case of the afterimage.

Form perception

Form perception means the experience of a shaped region in the field. Recognition means the experience that the shape is familiar. Identification means that the function or meaning or category of the shape is known. For those who have never seen the shape before, it will be perceived but not recognized or identified. For those who have, it will be perceived as a certain familiar shape and also identified. Recognition and identification obviously must be based on past experience, which means that through certain unknown processes, memory contributes to the immediate experience that one has, giving the qualities of familiarity and meaning.

The figure of a 4 in Fig. 1a is seen as one unit, separate from other units in the field, even if these units overlap. This means that the parts of the figure are grouped together by the perceptual system into a whole, and these parts are not grouped with the parts of other objects. This effect is called perceptional organization. There are other problems about form perception that remain to be unraveled. For example, the size of a figure can vary, as can its locus on the retina or even its color or type of contour, without affecting its perceived shape (Fig. 2).

Perceptual organization, (a) The figure of a four is immediately and spontaneously perceived despite the presence of other overlapping and adjacent lines, (b) The four, although physically present, is not spontaneously perceived and is even difficult to see when one knows it is there.
Perceptual organization, (a) The figure of a four is immediately and spontaneously perceived despite the presence of other overlapping and adjacent lines, (b) The four, although physically present, is not spontaneously perceived and is even difficult to see when one knows it is there.

Transposition of form; the two shapes clearly look the same despite the difference in size.

A further fact about form perception is that it is dependent upon orientation. It is a commonplace observation that printed or written words are difficult to read when inverted, and faces look very odd or become unrecognizable when upside down. Simple figures also look different when their orientation is changed: a square looks like a diamond when tilted by 45°.

Geometrical illusions

Related to the topic of form perception is the misperception of the size or direction of parts of figures that constitutes many of the geometric illusions. In an illusion figure, one particular part is perceived to be either longer or shorter than another part, although they are objectively equal (Fig. 3a); or the direction of a contour is perceived to be different from that of another contour although they are the same (Fig. 3b). For reasons still not understood, the background or context of the rest of the figure affects these parts.

Geometrical illusions, (a) The Ponzo illusion in which the two horizontal lines of equal length appear <ailnk tname= unequal, (b) The Poggendorff illusion in which the two oblique line segments are aligned with one another (that is, are collinear) but appear to be misaligned.">
Geometrical illusions, (a) The Ponzo illusion in which the two horizontal lines of equal length appear unequal, (b) The Poggendorff illusion in which the two oblique line segments are aligned with one another (that is, are collinear) but appear to be misaligned.

Innate or learned?

A central problem is whether the perception of properties such as form and depth or the achievement of veridical perception as in the constancies is innately determined or is based on past experience. By “innate” it is meant that the perception is the result of evolutionary adaptation and thus is present at birth or when the necessary neural maturation has occurred. By “past experience” it is meant that the perception in question is the end result of prior exposure to certain relevant patterns or conditions, a kind of learning process. Despite centuries of discussion of this problem, and considerable experimental work, there is still no final answer to the question. It now seems clear that certain kinds of perception are innate, but equally clear that past experience also is a determining factor. See also Intelligence.

Our senses probe the external world, and they also tell us about ourselves as they monitor the positions of our limbs and the balance of our bodies. Through pain they signal injury and illness.

How we experience and know about external objects is a question that was discussed by the Greek philosophers and has been ever since. Planned experiments on perception, in the spirit of the physical sciences, were hardly attempted before the mid nineteenth century. They have revealed a surprising complexity of physiological and cognitive (knowledge-based) processes, of which we are normally unaware, though many can be demonstrated simply and dramatically, especially through the phenomena of illusions.

There is a long-standing tradition in philosophy that perception, especially touch and vision, gives undeniably true knowledge. For philosophers have generally sought certainty and often claimed it, whereas scientists (who are used to their theories being upset by new data) are more ready to settle for today's best bet. Many scientific instruments have been developed because of the unreliability or inadequacy of perception.

Perceptions are separate, and in several ways different, from conceptual understanding, for perception must work very fast (whereas we may take minutes or hours to ‘make up our minds’, and years to form new concepts). Also, it would be impossible for perception to draw upon all of our knowledge; and perceptions are of individual objects and events in present time, while concepts are abstract and generally timeless.

The evolution of mechanisms for the perception of objects and events at a distance (most completely through vision and hearing) freed organisms from the tyranny of reflex responses to immediate situations, and no doubt was a necessary precursor of all intelligence. It is a fairly new notion that perception itself is an intelligent activity, requiring still only partly understood problem-solving to infer the objective world from sensory signals. Earlier accounts, especially British Empiricism, portrayed sensory perception very differently, as a passive, undistorting window, through which the mind accepts sensations directly from objects. This is not consistent with physiological knowledge of the senses and the brain, nor with many phenomena, such as illusions of vision and hearing and touch. The notion of ‘direct perception’ is, however, still maintained by some followers of the American psychologist J. J. Gibson, perhaps by taking this aspect of his important writings too literally. Perception is not traditionally thought of as an intelligent activity; though the power, especially of vision, to probe distance gains the time needed for intelligent behaviour and for the intelligence of perception itself.

Are perceptions simply picked up by the senses passively, or are they created actively by the brain, or mind? This issue between passive or active perception is a long-standing debate, with significant implications, such as: what is ‘objective’ and what ‘subjective’? The philosopher John Locke (1690) suggested that there are primary characteristics, such as hardness and mass and extension of objects, in space and time — in the world before life, existing apart from mind — and secondary characteristics, created in minds or brains. Thus colours are not in the world, but are created within us, though related in complex ways to light and to the surfaces of objects. Sir Isaac Newton (Opticks, 1704) expressed clearly that red light is not itself red, but is: ‘red-making’:

…there is nothing else than a certain power and disposition to stir up the sensation of this or that colour. For as sound in a bell or musical string … is nothing but a trembling motion.

Then (in Query 23 of Opticks) Newton speculates on something like a neural mechanism of vision:

Is not vision perform'd chiefly by the Vibrations of this (Eatherial) Medium, excited in the bottom of the eye of Rays of Light, and propagated through the solid, pellucid and uniform Capillamenta of the optic Nerves in the place (the ‘Sensorium’) of Sensation?

The Empiricist school (of which, in their different ways, Locke and Newton were founders) also rejected the notion that minds can receive knowledge by direct intuition quite apart from sensory experience. Mind was now regarded as essentially isolated from the physical world — linked only by tenuous threads of nerve and by fallible inferences of what might be ‘out there’. Some people find this too unsettling to be true. But it is now generally accepted that perception depends on active, physiologically based, intelligent processes. This is not intuitively obvious, since perception seems so simple and easy and we know nothing of the processes in our brains by introspection. Seeing happens so fast and so effortlessly that it is hard to conceive the complexity of the processes that we now know are needed to interpret the nature of the visual world from sensory signals — processes that remain largely beyond the capabilities of the most advanced computers.

Paradoxically, this takes us to concepts familiar to engineers and useful for physiology. We may describe the organs of the senses as ‘transducers’, which accept patterns of energy from the external world, signalling them as coded messages to be read by the brain, which uses these patterns to infer the state-of-play of the surrounding world, and something of the body's own states. Another useful engineering concept is that of ‘channels’. The various senses feed specialized ‘brain modules’ through neural channels, discovered by physiological and ‘psychophysical’ (perceptual) experiments. Thus, as Thomas Young suggested in 1801, colour vision is created from information about the wavelength of light transmitted through three channels, red, green, and blue, responding to light of long, medium, and short wavelength, respectively. All the hundreds of colours we can see are interpretations by the brain of the relative activity of these three colour channels. The three colour channels correspond, initially, to three kinds of light-catching photopigment in the photoreceptors, called cones, in the retina.

There are similar neural channels representing the orientation of lines and edges, and for movement, as first shown by direct physiological recording from nerve cells in the visual cortex of cats by the physiologists D. H. Hubel and T. N. Wiesel in 1962. There are channels for many other visual characteristics: stereoscopic (3-D) depth, texture, spatial size, etc. The ear has many different frequency channels, and there are scores of channels for the sense of ‘touch’, including those for various kinds of pain, for tickle, and for monitoring the positions of the limbs and the stretch of muscles in order to control movement. We are unaware of activity in these sensory channels themselves. Somehow outputs from the many channels are combined to give consistent perceptions. Small discrepancies — such as the delay in sound between seeing a ball hit a bat and hearing the impact — are rejected or pulled into place to maintain a consistent world. Equally, whole objects are somehow assembled from the many signals in different sensory channels that define them. But how this (‘the binding problem’) is done is not understood.

The theory that perception is ‘cognitive’, depending on inferences from essentially inadequate sensory signals, was first clearly proposed by the German polymath physicist, physiologist, and psychologist, Hermann von Helmholtz (1821-94). He called perceptions ‘unconscious inferences’. We might say that they (our most intimate experiences and knowledge) are simply hypotheses, essentially like the predictive hypotheses of science — though not always agreeing in particular accounts.

More recently, attempts to program computers to see (an important component of artificial intelligence) has shown how hard it is to infer objects from sensed data. The most influential attempt, by physiologist David Marr, suggested that object shapes are derived from the retinal images via three essential stages:

(i) the ‘primal sketch(es) ’, describing intensity changes and locations or critical features and local geometric relations;
(ii) the ‘2 ¹/₂-D sketch’, giving a preliminary analysis of depth, surface discontinuities, and so on, in a frame that is centred on the viewer;
(iii) the ‘3-D model representation’, in an object-centred co-ordinate system, so that we see objects much as they really are in 3-D space, though they are presented from just one viewpoint. Marr supposed that this last stage is aided by restraints on the range of likely solutions to the problem of what is ‘out there’. These information-processing constraints are set by assuming typical object shapes; for example, that the shapes of many objects, such as other human beings, are modified cylinders. Interestingly, the painter Paul Cézanne came close to this notion in 1904:

Treat nature by the cylinder, the sphere, the cone, everything in proper perspective so that each side of an object or a plane is directed towards a central point … nature for us men is more depth than surface.

David Marr stressed the importance of immediate, passive processing of sensory signals, over active, cognitive ‘top down’ application of knowledge gained from the past. This is a central controversy, currently moving towards greater cognitive ‘top down’ contributions, especially for vision. When computers (or the form of computing known as ‘neural nets’) can access vast amounts of knowledge appropriately, in real time, they might share our miracle of perception.

Artists and scientists can teach each other secrets of perception (as by Gombrich, 1960), though such cross-cultural communication is not easy for most of us.

— Richard L. Gregory

Bibliography

Gibson, J. J. (1950). Perception of the visual world. Houghton Mifflin, Boston MA.
Gibson, J. J. (1966). The senses considered as perceptual systems. Houghton Mifflin, Boston MA.
Gombrich, E. (1960). Art and illusion. Phaidon, London.
Gregory, R. L. (1966, fifth edn 1998). Eye and brain. Oxford University Press.
Hubel, D. and Wiesel, T. N. (1962). Receptive fields, binocular interaction and functional architecture in the cat's visual cortex. Journal of Physiology, 160, 106-54.
Marr, D. (1982). Vision. W. H. Freeman, San Francisco.
Zeki, S. (1993). A vision of the brain. Blackwell, Oxford

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In psychology and the cognitive sciences, perception is the process of acquiring, interpreting, selecting, and organizing sensory information. It is a task far more complex than was imagined in the 1950s and 1960s, when it was proclaimed that building perceiving machines would take about a decade, but, needless to say, that is still very far from reality. The word perception comes from the Latin perception-, percepio, , meaning "receiving, collecting, action of taking possession, apprehension with the mind or senses." --OED.com. Methods of studying perception range from essentially biological or physiological approaches, through psychological approaches through the philosophy of mind and in empiricist epistemology, such as that of David Hume, John Locke, George Berkeley, or as in Merleau Ponty's affirmation of perception as the basis of all science and knowledge.

There are two basic theories of perception: Passive Perception (PP) and Active Perception (PA). The passive perception (conceived by René Descartes) is addressed in this article and could be surmised as the following sequence of events: surrounding - > input (senses) - > processing (brain) - > output (re-action). Although still supported by mainstream philosophers, psychologists and neurologists, this theory is nowadays losing momentum. The theory of active perception has emerged from extensive research of sensory illusions with works of Professor Emeritus Richard L Gregory in a lead. This theory is increasingly gaining experimental support and could be surmised as dynamic relationship between “description” (in the brain) < - > senses < - > surrounding.

History of the study of perception

Perception is one of the oldest fields within scientific psychology, and there are correspondingly many theories about its underlying processes. The oldest quantitative law in psychology is the Weber-Fechner law, which quantifies the relationship between the intensity of physical stimuli and their perceptual effects. It was the study of perception that gave rise to the Gestalt school of psychology, with its emphasis on holistic approach. .

Perception and reality

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Many cognitive psychologists hold that, as we move about in the world, we create a model of how the world works. That is, we sense the objective world, but our sensations map to percepts, and these percepts are provisional, in the same sense that scientific hypotheses are provisional (cf. in the scientific method).

As we acquire new information, our percepts shift, thus solidifying the idea that perception is a matter of belief. Abraham Pais' biography refers to the 'esemplastic' nature of imagination. In the case of visual perception, some people can actually see the percept shift in their mind's eye. Others who are not picture thinkers, may not necessarily perceive the 'shape-shifting' as their world changes. The 'esemplastic' nature has been shown by experiment: an ambiguous image has multiple interpretations on the perceptual level.

Just as one object can give rise to multiple percepts, so an object may fail to give rise to any percept at all: if the percept has no grounding in a person's experience, the person may literally not perceive it.

This confusing ambiguity of perception is exploited in human technologies such as camouflage, and also in biological mimicry, for example by Peacock butterflies, whose wings bear eye markings that birds respond to as though they were the eyes of a dangerous predator. Perceptual ambiguity is not restricted to vision. For example, recent touch perception research (Robles-De-La-Torre & Hayward 2001) found that kinesthesia-based haptic perception strongly relies on the forces experienced during touch. This makes it possible to produce illusory touch percepts (see also the MIT Technology Review article The Cutting Edge of Haptics).

Cognitive theories of perception assume there is a poverty of stimulus. This (with reference to perception) is the claim that sensations are, by themselves, unable to provide a unique description of the world. Sensations require 'enriching', which is the role of the mental model. A different type of theory is the perceptual ecology approach of James J. Gibson. Gibson rejected the assumption of a poverty of stimulus by rejecting the notion that perception is based in sensations. Instead, he investigated what information is actually presented to the perceptual systems. He (and the psychologists who work within this paradigm) detailed how the world could be specified to a mobile, exploring organism via the lawful projection of information about the world into energy arrays. Specification is a 1:1 mapping of some aspect of the world into a perceptual array; given such a mapping, no enrichment is required and perception is direct.

Perception-in-Action

The ecological understanding of perception advanced from Gibson's early work is perception-in-action, the notion that perception is a requisite property of animate action, without perception action would not be guided and without action perception would be pointless. Animate actions require perceiving and moving together. In a sense, "perception and movement are two sides of the same coin, the coin is action." (D.N. Lee) A mathematical theory of perception-in-action has been devised and investigated in many forms of controlled movement by many different species of organism, General Tau Theory. According to this theory, tau information, or time-to-goal information is the fundamental 'percept' in perception.-

Perception and action

We gather information about the world and interact with it through our actions. Perceptual information is critical for action. Perceptual deficits may lead to profound deficits in action (for touch-perception-related deficits, see Robles-De-La-Torre 2006).

Types of perception

Amodal perception
Color perception
Depth perception
Form perception
Haptic perception
Speech perception
Perception as Interpretation
Numeric Value of Perception
Perceive

References and Further Reading

Flanagan, J.R., Lederman, S.J. Neurobiology: Feeling bumps and holes, News and Views, Nature, 412(6845):389-91 (2001).
James.J.Gibson, The Senses Considered as Perceptual Systems. Boston 1966.
James J. Gibson. The Ecological Approach to Visual Perception. Lawrence Erlbaum Associates, 1987. ISBN 0898599598
Hayward V, Astley OR, Cruz-Hernandez M, Grant D, Robles-De-La-Torre G. Haptic interfaces and devices. Sensor Review 24(1), pp. 16-29 (2004).
Robles-De-La-Torre G. & Hayward V. Force Can Overcome Object Geometry In the perception of Shape Through Active Touch. Nature 412 (6845):445-8 (2001).
Robles-De-La-Torre G. 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 (2006).

External links

Online papers on perception, by various authors, compiled by David Chalmers
Paradoxical haptic objects. An example of touch illusions of shape. See also the MIT Technology Review article:
The Cutting Edge of Haptics, by Duncan Graham-Rowe.
Theories of Perception
Richard L Gregory