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BottomUp Processing

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BottomUp Processing
121
Recognizing the Perceptual World
Recognizing the Perceptual World
䉴 How do I recognize familiar people?
In discussing how people organize the perceptual world, we have set the stage for
addressing one of the most vital questions that perception researchers must answer:
How do we recognize what objects are? If you are driving in search of Barney’s Diner,
exactly what happens when your eyes finally locate the pattern of light that spells out
its name?
To know that you have finally found what you have been looking for, your brain
must analyze incoming patterns of information and compare them with information
about the target that you have stored in memory. If the brain finds a match, recognition takes place. Once you recognize a stimulus as belonging to a particular category,
your perception of the stimulus may never be the same again. Look at Figure 3.25. Do
you see anything familiar? If not, turn to Figure 3.26; then look at Figure 3.25 again.
You should now see it in an entirely new light. The difference between your “before”
and “after” experiences is the difference between the sensory world before and after a
perceptual match occurs and recognition takes place.
How does this matching process occur? Some aspects of recognition begin at the
“top.” That is, they are guided by knowledge, expectations, and other psychological factors. This phenomenon is called top-down processing, because it involves high-level,
knowledge-based information. Other aspects of recognition begin at the “bottom,” relying
on specific, detailed information from the sensory receptors and assembling them into
a whole. This phenomenon is called bottom-up processing, because it begins with
basic information units that serve as a foundation for recognition.
Bottom-Up Processing
All along the path from the eye to the brain, certain cells respond to selected features
of a stimulus. The stimulus is first analyzed into these basic features, which are then
recombined to create the perceptual experience.
What are these features? As mentioned earlier, certain cells specialize in responding
to lines, edges, corners, and stimuli having specific orientations in space (Hubel &
Wiesel, 1979). For example, some cells in the cerebral cortex fire only in response to a
diagonal line, so they act as feature detectors for diagonal lines. The analysis by such feature detectors, early in the sensation-perception sequence, may contribute to recognition
FIGURE
3.25
Categorizing Perceptions
doing
2
learn
by
What do you see here? For the
identity of this figure, turn to
Figure 3.26.
top-down processing Aspects of
recognition guided by higher level cognitive processes and psychological factors such as expectations.
bottom-up processing Aspects of
recognition that depend first on information about stimuli that come up to
the brain from the sensory systems.
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