Is Perception Based on Unconscious Inferences?

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     Is Perception Based on Unconscious Inferences?

Perception and awareness of our surroundings are things we continually take for granted and without these abilities it would be impossible to navigate our way safely round our environment. Roth (1986) described perception as, “The means by which information acquired `via the sense organs is transformed into experiences of objects, events etc” This raises the question of how the sensory stimulation detected by our sense receptors is converted into conscious perceptual experience? Many theories of perception suggest that while the sensory pattern is dependent on the stimulus, it is often supplemented by other sources of information such as our knowledge and previous experience of the world and that inferences are made about the real world based on this information. This seemingly simple and effortless process has actually proved to be much more complex than first thought

Inferences are logical judgements “made on the basis of a sample of evidence, previous judgements, prior conclusions, etc. rather than on direct observation.” Inferences made unconsciously are defined as, “judgements made on the basis of a limited amount of evidence or data and made without awareness” (Reber and Reber, 2001) and were first articulated by Hermann Von Helmholtz (1867), who considered them to be a result of associations and experience. Through these ideas he pioneered the constructivist approach of perception which considered information from the senses to be insufficient in forming perceptual experience which, according to Helmholtz, required various cognitive processes. Unconscious inferences were thought to be the main processes involved in perception, adding meaning to the sensory input by unconsciously combining the information from the stimulus with other information to derive the perceived event.  These inferences were described as being unconscious because we are not usually aware of this process and we cannot change our perceptions at will. This introduced the idea that perception was not a passive process but required intelligent problem solving based on knowledge. Although Helmholtz did not fully develop this idea of unconscious inferences it was extremely influential and gave subsequent theorists a concept by which to explain the processes at work in perception. A modern and more detailed version of the constructivist approach is provided by Gregory (1973, 1978) who explained perception in terms of hypotheses forming and testing, predicting unsensed characteristics of objects. He proposed that signals received by sensory receptors triggered neural events and interacted with appropriate prior knowledge and it was on this combination of information that he believed hypotheses were made to predict events in the world. This concept of unconscious inference has been demonstrated by perceptual constancies and illusions.

The fact that we perceive a 3dimensional world from a 2dimensional image on the retina can be explained by the constructivist approach, using concept driven processes to fill in the gaps of information in the retinal image. Unconscious inferences allow behaviour to be appropriate to objects even though all the characteristics of that object may not be available in the stimulus. For example, a table can still be perceived as a table even if one of its legs is occluded and therefore not present in the proximal stimulus. The visual system ‘fills in’ the occluded portion rapidly and automatically inferring that the object is in fact still a table and behave towards it in the same way we would to any other table ( Gerbino and Salmaso, 1987). The size constancy mechanism works to maintain the perceived size of an object regardless of its reduction in size on the retina due to it being at a greater distance from the observer. This mechanism can be seen in a study by Ittleson (1951), where observers were presented with three playing cards in a darkened room, with depth cues removed. One of the cards was of normal size, another was half the size and the other was double the normal size. The largest card was judged to be closest to the observer and the smallest card was judged to be furthest away, even though they were all at the same distance. This suggests that as well as depth cues, familiar size information is used in conjunction with change in retinal image size to gain an impression of relative distance. The Ames room illusion (Ames, 1949) shows how perceptual hypotheses may be very inaccurate if the stimulus information appears familiar but is actually completely new. The room is an irregular shape with a sloping floor and one end of the rear wall much further from the viewer than the other end. However, when viewed through a peephole, the room creates the same retinal image as a normal rectangular room. The cues suggesting that the rear wall is at right angles to the viewer are so strong that observers tend to perceive the person inside the room as growing and shrinking as they walk across the room, rather than perceiving the room as being an unusual shape. Gregory suggested that this is because prior experience is of rooms of a rectangular shape and therefore hypotheses are formed based on the expected shape of the room. Although this explanation has been challenged (e.g. Day and Power, 1965), this remains a powerful demonstration of the vulnerability of perception and its inferential nature. Shape constancy ensures that we still perceive the correct shape of an object regardless of the shape produced on the retina due to the object being viewed from a particular angle. For example, however much you tilt your head you still perceive trees and telegraph poles as being vertical. Brightness constancy works, for example, to maintain the perception of coal as being black even in bright light, and paper as white, even in dark shadow. This is similar to colour constancy which allows familiar objects to retain their colour under a variety of lighting conditions.

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When and how a system breaks down is often used to give insight into how it normally operates which is why illusions have been used to give clues into the underlying processes in perception. Gregory’s theory accounts for a variety of visual illusions, of which he says there are four types; Illusions of ambiguity, paradox, distortion or fiction. Ambiguous illusions demonstrate how perception can be ambiguous since the same pattern of stimulation creates two different percepts through switch of attention. This is evidence that perception cannot be derived directly from the stimulus in a one to one manner. An example ...

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