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Date posted: November 30, 2011

Perception refers to the way the world looks round, feels taste or smell. In other words, perception can be defined as whatever is experienced by a person. In psychology and the cognitive sciences perception is the process of acquiring, interpreting, selecting and organizing sensory information. The word perception comes from the Latin perception-percepio meaning “receiving collecting, action of taking possession, apprehension with the mind or senses. Subjective experiences of objects or events ordinarily result from stimulation of the receptor organs of the body. This stimulation is transformed or encoded into neutral activity [by specialized receptor mechanism] and is relayed to more central regions of the nervous system where further neutral process occurs. Most likely, it is the final neutral processing in the brain that underlines or causes perceptual experience and so perception like experiences can sometime occur without external stimulation of the receptor organs, as in dreams.

Apart from five senses i.e. vision, hearing, taste, smell and touch, perception also applies to other sense modalities. In addition to touch the skin contains separate warmth, cold and pain senses further more the sense organs is the muscles, tendon and joints tells us about the position of limbs and state of tension in the muscles. Positions of the parts of the body are perceived with respect to one another whether they are stationary (proprioception) or in motion (kinesthesis). The vestibular sense informs us about the movement and stationary position of the head.

Catagories of perception

  • Internal perception (proprioception)

It tells us what’s going in our bodies.  E.g. we can sense if we are sitting, standing hungry etc

  • External perception (Exterpception)

It tells us about the world outside our bodies.

E.g. using our senses we can discover colours, sounds, textures etc. the philosophy of perception is mainly concerned with exteroception.

Scientific accounts of perception
The science of perception is concerned with how events are observed and interpreted. Our sense organs translate physical energy from the environment into electrical impulses processed the brain. For e.g. light in the form of electromagnetic radiation, causes receptor cells in our eyes to activate and send signals to the brain. But we do not understand these signals as pure energy. The process of perception allows us to interpret them as objects, events people and situations.

Dreams, imaginings and perception of similar things such as faces are accompanied by activity in many of the same areas of brain. Imaginary also involves higher level of cortical processing.

If an object is also a sources of sound this is transmitted a pressure waves that are sensed by the chochlear in the ear. The data from eye & ears is combined to form a ‘bound’ percept.

Theories of perception
Passive perception – (conceived by Rene Descartes) surmised as the following sequence of events.

Surrounding>input (sense)>processing (brain)>output (reaction).  Although still supported by mainstream philosophers, psychologists and neurologists, this theory is now days losing momentem.

Active perception-   Emerged from extensive research of sensory illusions with works of professor Emeritus Richard Gregory in a lead. This theory is increasingly gaining experimental support and could be surmised dynamic relationship between description (in the brain) <…> senses <…> surrounding.

Form perceptionFundamental process in form perception is the recognition of a figure on a ground. Pictures hang on a well, words are seen on a page and the melody stands out from the repetitive chords in the musical backgrounds. The pictures, words, and melody are perceived as the figure. While the wall, page and chords are the ground.

Contours in visual form perception
Contours are formed whenever a marked difference occurs in the brightness or colour of the background. 

If you look at a piece of paper that varies continuously in brightness from white at one border to black at the opposite border, you will perceive no contour. The paper will appear uniform, and if you are asked to say where the sheet stops being light and starts to become dark, you can only guess or be arbitrary. On the other hand, if the change is marked rather than gradual – suppose several shades are skipped – you will see the paper as divided into two parts, a light part and a dark part. In perceiving the division at the place where the brightness gradient changes abruptly, you have perceived a contour.

Contours give shape to the objects in our visual world because they mark one object off from another or they mark an object off from the general ground. When contours are disrupted visually, as in camouflage objects are difficult to distinguish from the background. But just because contours give shape to forms does not mean that contours themselves are shapes. The reversible faces of figure show the difference between contour and shape. Although both faces are formed by same contour, they obviously do not have the same shape. Contours determine shape, but by themselves they are shapeless.

While difference in energy levels of light across the retina are involved in the formation of most contours in everyday experience, it has been found that contours can contours can sometimes be seen without any energy difference at all on the two sides of the contour (Kanizsa, 1976; Coren, 1972). These are the so-called subjective contours. For example, in figure, you see the contours of the upright triangle even though there are no energy changes across its perceived borders except in the corners. Note that the three angles forming the corners of the inverted triangle do not generate a subjective contour.

ORGANIZATION IN FORM PERCEPTION
When several objects are presents in the visual field, we tend to perceive them as organized into patterns or groupings. Gestalt psychologists said that “the whole is more than the sum of its parts”. This simply means that what is perceived has its own new properties, properties that emerge from the organization which takes place.

Organization in perception partially explains our perception of complex patterns as unitary forms, or objects. We see objects as object only because grouping processes operate in perception. Without them, the various objects and patterns we perceive- a face on television screen, a car, a tree, a book- would not “hang together” as objects or patterns. They would merely be so many disconnected sensations- dots, lines, or blotches, for example.

One organizing principle is proximity, or nearness. In figure we see three pairs of vertical lines instead of six single lines. The law of proximity says that items which are close together in space or time tend to be perceived as belonging together or forming an organized group.

Another organizing principle of perception- similarity. In b, most people see one triangle form by dots with its apex at the top and another triangle formed by the rings with its apex at the bottom. They perceive triangles because similar items- the dots and rings- tend to be organized together otherwise they would see figure has hexagon or a six pointed star, like figure where all the dots are the same.

Grouping according the similarity, however, does not always occur. The figure in is more easily seen as a six pointed star than as one figure composed of dots and another figure made up of rings. In this case, similarity is competing with the organizing principle of symmetry, or good figure. Neither the circles the dots by themselves form a symmetrical pattern. The law of good figure says that there is a tendency to organize things to make a balanced or symmetrical figure that includes all the parts. In this case such a balanced figure can be achieved only by using all the dots and rings to perceive a six-pointed star. The law of good figure wins out over the law of similarity because the rings by themselves or the dots by themselves do not form symmetrical good figures.

 Another principle of organization is continuation, the tendency to perceive a line that stars in one way as continuing in the same way. Figure illustrates this principle of continuation: we see the dots as several curved and straight line suddenly becoming a curved line at one of these junctions.

 The law of closure makes our perceived world to form more complete than the sensory stimulation that is presented. The law of closure refers to perceptual processes that organize the perceived world by filling in gap in stimulation. By the action of these processes, we perceive a whole form, not disjointed parts. In figure, for example, the left-hand drawing is seen as a circle with gaps in it-not simply as disconnected lines. The principle of closure also applies to perception of the pattern at right in figure. Here again, we fill in the gaps and perceive form rather than disconnected lines. (Most people see a figure on the horse back.)

Although the examples ii figure is visual, the same principles of grouping can be observed in the other senses. In all these laws of organization, the principle of the Gestalt psychologists that “the whole is more than the sum of its parts” can be observed at work.

PERCEPTION PROCESS – VISUAL DEPTH PERCEPTION

  • Perceiving Distance
  • We determine distance using two different cues: monocular or binocular
  • Monocular cues
  • Monocular cues are those cues which can be seen using one eye. They include size; texture, overlap shading, height, and clarity 

Linear Perspective: The distances separating the images of far objects appear to be smaller. Imagine that you are standing between railroad tracks and looking off into the distance. The ties would seem to run closer and closer together until they appeared to meet at the horizon. Figure owes part of its depth effect to such linear perspective.

Clearness: In general, the more clearly we see an object, the nearer it seems. A distant mountain appears farther away on a hazy day than it does on a clear day because haze in the atmosphere blurs fine details and we see only the larger features

Interposition:  Still another monocular cue is interposition, which occurs when one object obstructs our view of another. When one object is completely visible while another is partially covered by it, the first object is perceived as nearer

Shadows: the pattern of shadows or highlights in an object is very important in giving an impression of depth.

Gradient of Texture:  A gradient is a continuous change in something- a change without abrupt transitions. The regions closest to the observer have a coarse texture and many details; as the distance increases, the texture becomes finer and finer. This continuous gradation of texture gives the eye and brain information that can used to produce an experience, or perception, of depth.

Movement:  When you move your head, you will observe that the objects in your visual field move relative to you and to one another. If you watch closely, you will find that objects nearer to you than the spot at which you are looking- the fixation point- move in a direction opposite to the direction in which your head is moving.

A binocular cue for depth perception
Binocular cues refer to those depth cues in which both eyes are needed to perceive. There are two important binocular cues; convergence and retinal disparity. Convergence refers to the fact that the closer an object, the more inward our eyes need to turn in order to focus. The farther our eyes converge, the closer an object appears to be. Since our eyes see two images which are then sent to our brains for interpretation, the distance between these two images, or their retinal disparity, provides another cue regarding the distance of the objects.

Perceptiual processes constancy
By an large, these perceptual properties of object 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 serves to characterize field of perception, serves to characterize field of perception. There are typically three constancies including size, shape and brightness others are orientation and position

SIZE CONSTANCY refers to our ability to see objects as maintaining the same size even when our distances from them makes things appear larges or smaller. This holds true for all of our senses. As we walk away from our radio. The song appears to get softer. We understand & perceive it as being just as loud as before.

SHAPE CONSTANCY.
A plate in a form of circle looks like an ellipse from an angle. Shape constancy allows us to perceive that plate as still being a circle even though the angle from which we view it appears to distort the shape.

BRIDHTNESS CONSTANCY
Refers to our ability to recognize that colour remains the same regardless of how it looks under different levels of light. Example Deep blue you wore to the beach suddenly looks black when you walk indoors. Without colour constancy, we should be constantly re interpreting colour and would be amazed at the miraculous conversion our clothes undertake.

Orientation objects appear to keep the same orientation in space, independently of the orientation of the observers head.

Position- A fixed object remains perceived as stationary even when its image on the retina moves because of eye or head movements.

MOVEMENT PERCEPTION
 Perceived movement cannot simply be explained by the motion of an objects retinal image since image motion caused by observer or eye movement does not lead to perceive eye movement. Perceived movements can be

1) Apparent motion- Occurs without any energy movement across the receptor surface.

2)  Real motion- it involves active processing of the sensory input

Stroboscopic motion the kind seen in movies and on television is a common example of apparent motion.

An induced movement occurs of a spot or object is a perceived as moving when its frame or background moves.

Plasticity
Plasticity refers to the modifiability or mold ability of perception special situations, such as prolonged changes in sensory input, can modify the way information is processed in generating perceptions of the world around us.

SET
Refers to the idea that we may be “ready” and primed for certain times of sensory input.  It varies from person to person.  By giving people different predispositions, or sets, what is first perceived can be changed?

MOTIVES AND NEEDS
Peoples motive will to some extent, affect the ways in which they organize and perceive the test stimuli.

Disorders of perception

1)      HALLUCINATIONS – False perception of a sensory stimulus any sensory modality can be involved

  • a) Auditory hallucinations- seen in psychosis, alcoholic hallucinosis, schizophrenia.
  • b) Visual hallucinations- seen with organized psychosis, especially toxic or drug related states.
  • c)  Equstatory (taste) and olfactory hallucinations are mainly due to disorder of the temporal lobe.
  • d) Tactile hallucinations seen in organic states such as alcohol withdrawal or cocaine and amphetamine abuse. E.g. formication.
  • e) Kinesthetic hallucinations include feeling movements when none occurs. E.g. out of body experience described in near death situations may be kinesthetic hallucinations.
  • f) Hallucinations of any type that occur proceeding sleep or going to sleep termed hypnagogic and on awakening or getting up from sleep termed hypnoponpic occur  in normal individuals are not considered serious or pathologic.

 2) ILLUSIONS are misinterpretations of actual sensory stimulus

  • Examples driving down on a dry road and observing water patches, several hundred feet ahead of you and driving closer having them disappear. Occur in schizophrenia but most common in delirium

3)  DEPERSONALIZATION AND DEREALIZATION

  • They are attractions or abnormalities in an individual’s perception of reality.
  • Derealization – Alterations in the patients sense of reality of the outside world.
  • Depersonalization – An attraction in the perception of self feels strange and unreal, once reality is temporarily changed or lost. 

4) SOMATIC PASSIVITY PHENOMENON
Presence of strange sensations described by the patient as being imposed on the body by some external agency with the patient being a passive recipient

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