Behavioral enhancement of visual responses in monkey cerebral cortex. I. Modulation in posterior parietal cortex related to selective visual attention.

that area 7 of posterior parietal cortex plays a role in visual attention and eye movements. We have operationally defined attention as a stimulus-selection process independent of the specific movement used to respond to the stimulus. We trained monkeys to make various hand or eye movements and recorded from single neurons in area 7 while the monkeys were performing these tasks. 2. As demonstrated previously ( 19, 20, 46, 47, 63), many cells in area 7 respond to visual stimuli independent of any behavior. The discharge to a stimulus may be enhanced when the animal makes an eye movement to the stimulus. 3. We used two paradigms to study the modulation of visual responses when the animal used a stimulus without making an eye movement. The first was a peripheral-attention task in which the animal had to signal the occurrence of a peripheral stimulus without making an eye movement to it. Half of the cells studied gave an enhanced response in this task. In the second task, the animal had to reach out and touch a stimulus without making an eye movement to it. Visually responsive parietal neurons also yielded enhanced responses in this task. 4. The enhancements demonstrable in the saccade, peripheral-attention, and handreach tasks probably represent the same underlying process because their frequency of occurrence in our sample is almost identical, the intensities are quite similar, and cells that give an enhanced response on one task give an enhanced response in the others. 5. These results show that in posterior parietal cortex, the behavioral enhancement of a visual response is independent of the specific movement used to respond to the stimulus. The physiological mechanism of enhancement, which is movement independent and spatially selective, resembles the psychological phenomenon of selective spatial attention. We suggest that the role of area 7 in visual attention may be mediated by the enhancement of visual responses to selected stimuli.