Abstract
When exploring a visual scene, attention can be allocated to different regions according to the attentional priority of the objects in the scene. These priorities are represented in the lateral intraparietal area (LIP). It’s also well established that V4 responses are modulated by attention. We asked how neurons in these areas respond when attention is focused or spread while animals perform a change blindness task. In this task, an array of 1, 2, 4 or 8 oriented bars was flashed for 500 ms at equal eccentricities. After a gap of 50-300 ms, the bars reappeared for 1000 ms. In some trials, one of the bars had rotated 90 deg. The animal had to saccade to this bar to be rewarded. In the remaining trials, no bar was rotated and the animal was rewarded for maintaining fixation. Performance decreased as the number of bars increased, suggesting that attention was spread and that the attentional resources at each location decreased. Accordingly, LIP responses showed a set-size effect, with decreasing activity as the number of bars increased. However, V4 activity did not differ as a function of set size, suggesting that the decrease in behavioral performance is the result of down-stream processing rather than an attentional effect in visual cortex. In another block of trials, one of the locations was loaded by a significantly larger reward: a "hot spot". Attention was biased toward the hot spot in both subjects, resulting in an increase in both performance and neuronal responses in both V4 and LIP. This result suggests that traditional attentional modulation can still be elucidated in both LIP and V4 while the animals are performing this task. We conclude that covert attention acts to affect down-stream processes in addition to its known role in modulating responses in early visual areas.
Meeting abstract presented at VSS 2012