Dissociating Components of Visuo-Spatial Attention

Abstract

Neuronal signals related to visuo-spatial attention are found in widespread brain regions, and these signals are generally assumed to participate in a common mechanism of attention. However, the effects of visuo-spatial attention on the behavioral performance of human and animal observers can be separated into two distinct components. When a subject directs its attention to a visual location, the subject can change either its criterion or its sensitivity between the attended and unattended locations. I first found that when monkeys are trained to do a variant of the Posner attention paradigm, a task used in many single-neuron studies of visuo-spatial attention, enhanced performance is typically associated with both changes in the subject’s criterion and changes in its sensitivity. This finding indicates that the neuronal modulations attributed to visuo-spatial attention in previous studies could be associated with a behavioral change in sensitivity, a change in criterion, or a combination of both. To measure how neuronal signals across the brain are associated with the two components of attention, I designed a task to isolate attentional changes in either the criterion or the sensitivity of the subject. While monkeys were performing this task, I recorded from area V4 of their visual cortex and found that attention-related neuronal modulations in V4 corresponded to behavioral changes in sensitivity, but not changes in criterion. Subsequently, I recorded from prefrontal cortex (areas 45 and 46) and found that unlike V4, visual responses in prefrontal cortex were modulated when either the animal’s sensitivity or its criterion was changed between visual locations. Either an enhancement in sensitivity or a liberal change in criterion was associated with an increase in the firing rates of visual neurons in prefrontal cortex. These findings show that attention-related neuronal signals across the brain are not equivalent in their contribution to the mechanisms of visuo-spatial attention. Neuronal modulations in prefrontal cortex contribute to behavioral changes in both criterion and sensitivity, while modulations in visual cortex contribute to only changes in sensitivity. The results indicate that visuo-spatial attention is not a single neurobiological process but instead consists of at least two separable mechanisms mediated by overlapping groups of brain structures.