106 • CHAPTER 4 Attention
When I describe this process in class, some students aren’t convinced.
One student said, “I think that when people look at an object, they don’t
break it into parts. They just see what they see.” To convince this student
(and the many others who, at the beginning of the course, are not comfort-
able with the idea that cognition sometimes involves rapid processes we
aren’t aware of), I describe the case of R.M., a patient who had parietal lobe
damage that resulted in a condition called Balint’s syndrome. The crucial
characteristic of Balint’s syndrome is an inability to focus attention on indi-
vidual objects.
According to feature integration theory, lack of focused attention would
make it diffi cult for R.M. to combine features correctly, and this is exactly
what happened. When R.M. was presented with two different letters of dif-
ferent colors, such as a red T and a blue O, he reported illusory conjunctions
such as “blue T” on 23 percent of the trials, even when he was able to view
the letters for as long as 10 seconds (Friedman-Hill et al., 1995; Robertson
et al., 1997). The case of R.M. illustrates how a breakdown in the brain can reveal pro-
cesses that are not obvious when the brain is functioning normally.
The feature analysis approach involves mostly bottom-up processing because
knowledge is usually not involved. In some situations, however, top-down processing
can come into play. For example, when Treisman did an illusory conjunction experi-
ment using stimuli such as the ones in ● Figure 4.35 and asked participants to identify
the objects, the usual illusory conjunctions occurred; the orange triangle, for example,
would sometimes be perceived to be black. However, when she told participants that
they were being shown a carrot, a lake, and a tire, illusory conjunctions were less likely
to occur, and participants were more likely to perceive the triangular “carrot” as being
orange. In this situation, the participants’ knowledge of the usual colors of objects
infl uenced their ability to correctly combine the features of each object. In our everyday
experience, in which we are often perceiving familiar objects, top-down processing
combines with feature analysis to help us perceive things accurately.The Physiology of Attention
A great deal of research has studied the physiological mechanisms of attention. Two
important results are that (1) attention enhances neural responding, and (2) attentional
processing is distributed across a large number of areas in the brain.COVERT ATTENTION ENHANCES NEURAL RESPONDING
Most research investigating how attention affects neural responding has studied how
neural responding is affected by shifting attention covertly—that is, without eye move-
ments. The reason for using covert tasks when studying how attention affects neural
responding is that the eye movements that accompany overt attention cause a change
in the image on the retina, which can cause a neural response. Thus, to be sure that any
neural responses are caused not by changes in the image on the retina but by changes
in attention, researchers use a covert attention procedure in which the eyes remain
stationary.
In a covert attention experiment on monkeys, Carol Colby and coworkers (1995)
trained a monkey to keep its eyes fi xated on a dot (see ● Figure 4.36) while a peripheral light
was fl ashed at a location off to the right. In the “fi xation only” condition (Figure 4.36a),
the monkey’s task was to continue looking at the fi xation light and to release its hand
from a bar when the fi xation light dimmed. In the “fi xation and attention” condition
(Figure 4.36b), the monkey also kept looking at the fi xation light but released the bar
when the peripheral stimulus light dimmed. Thus, in the fi xation and attention condition,
the monkey had to pay attention to what was happening off to the side.● FIGURE 4.35 Stimuli used to show that
top-down processing can reduce illusory
conjunctions. (Source: Reprinted from A. Treisman &
H. Schmidt, “Illusory Conjunctions in the Perception of
Objects,” Cognitive Psychology,14, 107–141, 1982, with
permission from Elsevier.)Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.