Attentional modulation of behavioral performance and neuronal responses in middle temporal and ventral intraparietal areas of macaque monkey.

Although many studies have demonstrated that neuronal responses are modulated by attention, the significance of this modulation for behavior is poorly understood. We recorded from neurons in the middle temporal (MT) and ventral intraparietal (VIP) areas in the visual cortex of two macaque monkeys while they performed a motion detection task under two conditions of spatial attention. The ability of the animals to detect the motion was reduced when they withdrew attention from the stimulus. Withdrawing attention also reduced neuronal responses to the motion in both the MT and VIP areas. To compare the neuronal and behavioral effects of attention, the amount of attentional modulation was expressed in units of stimulus strength. On average, attention modulated neuronal responses in MT less than needed to account for the attentional effect on behavior. The opposite was observed in VIP, where the average effect of attention on neuronal responses was greater than that needed to account for behavior. Similar results were obtained when the effects of attention on neuronal response and behavioral performance were compared using a parametric function of stimulus strength. Across neurons in both areas, attentional modulation of neuronal responses was more variable than, and uncorrelated with, attentional modulation of behavioral performance. These findings suggest that attention can alter the average relationship between neuronal activity in visual cortex and behavioral performance. Where this relationship is preserved may indicate which cortical regions are most closely associated with the behavior in a given task.