Cognitive Psychology: Connecting Mind, Research and Everyday Experience, 3rd Edition

The Physiology of Attention • 107

As the monkey was performing these tasks, Colby recorded from a neuron in the

parietal cortex that fi red to the peripheral light. The records in Figure 4.36 show that

this neuron responded poorly when the monkey was not paying attention to the light

but that the response increased when the monkey shifted its attention off to the side—

even though it was still looking directly at the fi xation light. Because the image of the

light on the monkey’s retina was always the same, the greater response when the mon-

key was paying attention to the peripheral light must have been caused by the monkey’s

attention to the light (also see Desimone & Duncan, 1995; McAdams & Reid, 2005;

Moran & Desimone, 1985). This result means that a neuron’s response can be affected

not just by which receptors are stimulated but also by other factors, such as whether

the observer is interested in the stimulus or whether the stimulus is important for car-

rying out a task.

This larger response due to attention to a stimulus has also been demonstrated in

humans using fMRI. We will now describe an experiment that shows both that atten-

tion enhances responding and that this attentional enhancement occurs in many areas

in the visual system.

ATTENTIONAL PROCESSING

IS DISTRIBUTED ACROSS THE CORTEX

Gordon Shulman and coworkers (1999) showed that attention to a particular

direction of motion increases activity in a number of brain structures. Using fMRI,

they  measured participants’ brain activity while participants performed a task in

which they paid attention to a specifi c direction of motion. Participants saw either

(1) a cue that alerted them to pay attention to a particular direction of motion or

(2) a cue indicating that they should just passively observe the display on the screen

(● Figure 4.37a). Following the cue, participants saw random motion, which was

created by a fi eld of dots that were moving in random directions (like the snow on a

TV set that isn’t tuned to a channel). After about a second, some of the dots started

moving in the cued direction of motion, a condition called coherent motion because

a number of dots were moving in the same direction. If the participants had seen

● FIGURE 4.36 To p: Stimuli for Colby et al.’s (1995) selective attention experiment. The monkey always looked at the

fi xation light on the left. A peripheral stimulus light was fl ashed inside the circle on the right. Below: (a) Nerve fi ring

when the monkey was looking at the fi xation light but was not paying attention to the peripheral light; (b) fi ring when

the monkey was looking at the fi xation light and was paying attention to the peripheral light. (Source: C. L. Colby, J. R.

Duhamel, & M. E. Goldberg, “Oculocentric Spatial Representation in Parietal Cortex,” Cerebral Cortex, 5, 470–481, 1995. Copyright © 1995 Oxford

University Press. Reprinted with permission from Oxford University Press.)

Time 200 ms

Fixation only Fixation and attention

Peripheral stimulus light Peripheral stimulus light

(ATTEND)

(a) (b)

Fixation light (LOOK AND ATTEND) Fixation light (LOOK)

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