Transcription of THEORIES OF PERCEPTION
1 1 THEORIES OF PERCEPTIONIn order to receive information from the environment we are equipped with sense organs eg eye,ear, nose. Each sense organ is part of a sensory system which receives sensory inputs andtransmits sensory information to the brain. A particular problem for psychologists is to explainthe process by which the physical energy received by sense organs forms the basis of perceptualexperience. Sensory inputs are somehow converted into perceptions of desks and computers,flowers and buildings, cars and planes; into sights, sounds, smells, taste and touch major theoretical issue on which psychologists are divided is the extent to which perceptionrelies directly on the information present in the stimulus. Some argue that perceptual processesare not direct, but depend on the perceiver's expectations and previous knowledge as well as theinformation available in the stimulus itself.
2 This controversy is discussed with respect to Gibson(1966) who has proposed a direct theory of PERCEPTION which is a 'bottom-up' theory, andGregory (1970) who has proposed a constructivist (indirect) theory of PERCEPTION which is a 'top-down' PERCEPTION - A TOP-DOWN APPROACHH elmholtz (1821-1894) is considered one of the founders of perceptual research. He argued thatbetween sensations and our conscious PERCEPTION of the real world there must be intermediateprocesses. Such processes would be, for example, 'inferential thinking' - which allows us to gobeyond the evidence of the senses (these inferences are at an unconscious level). Thus Helmholtzwas an early Constructivist who believed PERCEPTION is more than direct registration ofsensations, but that other events intervene between stimulation and early illustration that supports the idea of perceptions as modifiable constructions rather thanthe direct responses to pattern of stimulation is the 'Ames Room'.
3 This room is of an irregularshape with a receding rear wall and decorated in a special manner. C B AOne explanation for the Ames Room illusion is that the perceiver is in a situation of having tochoose between two beliefs built up through experience - (a) rooms that look rectangular andnormal, usually are just that, (b) people are usually of 'average' size. Most observers choose (a)and therefore consider the people to be 'odd'.The interesting thing about the Ames Room illusion is that it does not disappear when you learnthe true shape of the true wall, AC on the diagram, isdecorated so as to appear to be in theposition AB. Viewed from the frontpeephole with one eye the room appears tobe rectangular but a person moving fromA to C will appear to Point2 PERCEPTIONS AS HYPOTHESES - R L GREGORY (B 1923)Gregory proposes that perceiving is an activity resembling hypothesis formation and testing.
4 Hesays that signals received by the sensory receptors trigger neural events, and appropriateknowledge interacts with these inputs to enable us to makes sense of the has presented evidence in support of his theory, some of which is outlined below:1. ' PERCEPTION allows behaviour to be generally appropriate to non-sensed objectcharacteristics'.For example, we respond to certain objects as though they are doors even though we can only seea long narrow rectangle as the door is 'Perceptions can be ambiguous'The Necker cube is a good example of this. When you stare at the crosses on the cube theorientation can suddenly change, or flip'. It becomes unstable and a single physical pattern canproduce two argues thatsurely to do this wemust be using more thanjust sensory do we know fromthis stimulus alone thatthis is a door?33. 'Highly unlikely objects tend to be mistaken for likely objects'.
5 Gregory has demonstrated this with a hollow mask of a face. Such a mask is generally seen asnormal, even when one knows and feels the real mask. There seems to be an overwhelming needto reconstruct the face, similar to Helmholtz's description of 'unconscious inference'.What we have seen so far would seem to confirm that indeed we do interpret the information thatwe receive, in other words, PERCEPTION is a top down process. However:..EVALUATION OF THE TOP-DOWN APPROACII TO PERCEPTION1. The Nature of Perceptual HypothesesIf perceptions make use of hypothesis testing the question can be asked 'what kind of hypothesesare they?' Scientists modify a hypothesis according to the support they find for it so are we asperceivers also able to modify our hypotheses? In some cases it would seem the answer is example, look at the figure below:4 This probably looks like a random arrangement of black shapes.
6 In fact there is a hidden face inthere, can you see it? The face is looking straight ahead and is in the top half of the picture in thecentre. Now can you see it? The figure is strongly lit from the side and has long hair and a the face is discovered, very rapid perceptual learning takes place and the ambiguouspicture now obviously contains a face each time we look at it. We have learned to perceive thestimulus in a different in some cases, as in the ambiguous face picture, there is a direct relationship betweenmodifying hypotheses and PERCEPTION , in other cases this is not so evident. For example, illusionspersist even when we have full knowledge of them ( the inverted face, Gregory 1974). Onewould expect that the knowledge we have learned (from, say, touching the face and confirmingthat it is not 'normal') would modify our hypotheses in an adaptive manner. The currenthypothesis testing THEORIES cannot explain this lack of a relationship between learning Perceptual DevelopmentA perplexing question for the constructivists who propose PERCEPTION is essentially top-down innature is 'how can the neonate ever perceive?
7 ' If we all have to construct our own worlds basedon past experiences why are our perceptions so similar, even across cultures? Relying onindividual constructs for making sense of the world makes PERCEPTION a very individual andchancy constructivist approach stresses the role of knowledge in PERCEPTION and therefore is againstthe nativist approach to perceptual development. However, a substantial body of evidence hasbeen accrued favouring the nativist approach, for example:Newborn infants show shape constancy (Slater & Morison, 1985); they prefer their mother'svoice to other voices (De Casper & Fifer, 1980); and it has been established that they prefernormal features to scrambled features as early as 5 minutes after Sensory EvidencePerhaps the major criticism of the constructivists is that they have underestimated the richness ofsensory evidence available to perceivers in the real world (as opposed to the laboratory wheremuch of the constructivists' evidence has come from).
8 Constructivists like Gregory frequently use the example of size constancy to support theirexplanations. That is, we correctly perceive the size of an object even though the retinal image ofan object shrinks as the object recedes. They propose that sensory evidence from other sourcesmust be available for us to be able to do , in the real world, retinal images are rarely seen in isolation (as is possible in thelaboratory). There is a rich array of sensory information including other objects, background, thedistant horizon and movement. This rich source of sensory information is important to thesecond approach to explaining PERCEPTION that we will examine, namely the direct approach toperception as proposed by DIRECT APPROACH TO PERCEPTION - GIBSON 1966 Gibson claimed that PERCEPTION is, in an important sense, direct. He worked during World War IIon problems of pilot selection and testing and came to realise:In his early work on aviation he discovered what he called 'optic flow patterns'.
9 When pilotsapproach a landing strip the point towards which the pilot is moving appears motionless, with therest of the visual environment apparently moving away from that outflow of the optic array in a landing to Gibson such optic flow patterns can provide pilots with unambiguous informationabout their direction, speed and important components of Gibson's Theory are 1. Optic Flow Patterns; 2. InvariantFeatures; and 3. Affordances. These are now Light and the Environment - Optic Flow PatternsChanges in the flow of the optic array contain important information about what type ofmovement is taking place. For example:2 Any flow in the optic array means that the perceiver is moving, if there is no flow theperceiver is The flow of the optic array will either be coming from a particular point or moving towardsone. The centre of that movement indicates the direction in which the perceiver is moving.
10 Ifa flow seems to be coming out from a particular point, this means the perceiver is movingtowards that point; but if the flow seems to be moving towards that point, then the perceiveris moving away. See above for moving towards an object, below is moving away:The Optic Flow pattern for a person looking out of the back of a The role of Invariants in perceptionWe rarely see a static view of an object or scene. When we move our head and eyes or walkaround our environment, things move in and out of our viewing fields. Textures expand as youapproach an object and contract as you move away. There is a pattern or structure available insuch texture gradients which provides a source of information about the environment. This flowof texture is INVARIANT, ie it always occurs in the same way as we move around ourenvironment and, according to Gibson, is an important direct cue to depth. Two good examplesof invariants are texture and linear AffordancesAre, in short, cues in the environment that aid PERCEPTION .
