Perception

Chapter 12 Perception


Why do we perceive what we do? How does the brain process information so that what we see or hear is what we create, not what is actually ‘out there’? This spread shows how perception is not a passive process, but is active, creating and constructing our world. Whereas sensation (the stimulus which impacts upon the sense organs) provides the raw data about the environment, it is perception which provides meaning.


The main emphasis in this spread will be on visual perception, but these points also apply to other types of perception such as auditory, olfactory or tactile perception.



The main features of perception



image Perception is knowledge-based and partly learned. Early works of art show that artists (and young children) have to learn about perspective; likewise, your perception of pathological signs on a slide under a microscope improves with medical education.

image Perception is inferential. When we see part of an object, like the top half of a person sitting at a table, we perceive this as a ‘whole’ person, not half a person. A lot of what we perceive is effectively guesswork, which can have dangerous consequences.

image It is categorical. We tend to categorize what we see, so that a variety of clinical signs are perceived as a disease in a patient, even though they may not in fact be related.

image Perception is relational. What we perceive as small or large depends on context. A 2-cm flesh wound on a thigh is seen as less serious than the same size of wound on a finger.

image Perception is adaptive. We tend to perceive significant things better than insignificant things. For example, we notice a car which is moving more than we notice a stationary vehicle: this is more important for our survival.


What are illusions, and why are we subject to them?


Illusions demonstrate how creative a process perception is, because the stimuli are ambiguous, or presented a context which distorts our perception. Figure 1 illustrates this.


image

Fig. 1 In these two figures, the sets of horizontal lines are the same length, but we see them as differing lengths according to the rest of the drawing.


We are subject to illusions, not because we are unintelligent or not paying attention, but because the brain interprets reality in the light of our prior experience. This is important because different people perceive things differently, and not necessarily because one is wrong and one is right.



How do we recognize what is perceived?


Recognition is organizing what is perceived into something meaningful by using past experience. A number of theories exist to explain this:


image Bottom-up processing. The perceptual system is assumed to analyse a stimulus into a set of features and then the brain matches it to other sets already existing in the brain. If a match occurs, then there is recognition. In examining a rash, a general practitioner takes note of the shape, type, size, colour and distribution of spots on the skin, then matches them to previous cases of measles that s/he has seen, or the colour illustration and description of measles that s/he has seen in a textbook.

image Top-down processing. The context creates expectancy and sets up what is known as perceptual set

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Jun 10, 2016 | Posted by in PSYCHOLOGY | Comments Off on Perception

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