Abstract
Distinct neural systems process motivation and attention. At the behavioral level, however, both attention and motivation influence the reaction times of monkeys orienting to visual targets. Similarly, both attention and motivation enhance neuronal responses to visual targets in several visual and oculomotor brain areas in monkeys. Since both attention and motivation are conditioned by fluid rewards in such studies, the extent to which modulations in neuronal activity reflect attention or motivation remains unclear. Distinguishing these requires orthogonal manipulations of attention and reward. We attempted to distinguish motivational from attentional modulations in neuronal activity in area LIP in rhesus monkeys by training them shift gaze to visual targets while attention was manipulated exogenously and reward size was varied. Monkeys shifted gaze to a peripheral visual target 100–800 ms (SOA) after the illumination of a non-predictive visual cue either at the target location (valid condition) or diametrically opposed with regard to fixation (invalid condition). Small, medium, and large rewards were cued on each trial by the color and shape of the fixation stimulus. Saccade latencies were faster on valid than invalid trials, suggesting capture of attention by the peripheral cue; and also decreased with increasing reward, suggesting enhanced motivation. Importantly, there was no interaction between the effects of attention and motivation on reaction times. In preliminary neurophysiological data, the responses of LIP neurons were enhanced when validly cued targets appeared in their response fields and when saccade latency into the RF was decreased, but were only weakly modulated by reward size.