Response of neurons in the lateral intraparietal area to a distractor flashed during the delay period of a memory-guided saccade

Recent experiments raised the possibility that the lateral intraparietal ar ea (LIP) might be specialized for saccade planning. If this was true, one w ould expect a decreased sensitivity to irrelevant visual stimuli appearing late in the delay period of a memory-guided delayed-saccade task to a targe t outside the neurons' receptive fields. We trained two monkeys to perform a standard memory-guided delayed-saccade task and a distractor task in whic h a stimulus flashed for 200 ms at a predictable time 300-100 ms before the end of the delay period. We used two locations, one in the most active par t of the receptive field and another well outside the receptive field. We u sed six kinds of trials randomly intermixed: simple delayed-saccade trials into or away from the receptive field and distractor trials with saccade ta rget and distractor both in the receptive field, both out of the receptive field, or one at each location. This enabled us to study the response to th e distractor as a function of the monkey's preparation of a memory-guided d elayed-saccade task. We had assumed that the preparation of a saccade away from the receptive field would result in an attenuation of the response to the distractor, i.e., a distractor at the location of the saccade goal woul d evoke a greater response than when it appeared at a location far from the saccade goal. Instead we found that neurons exhibited either a normal or a n enhanced visual response to the distractor during the memory period when the target flashed outside the receptive field. When the distractor flashed at the location of the saccade target, the response to the distractor was either unchanged or diminished. The response to a distractor away from the target location of a memory-guided saccade was even greater than the respon se to the same target when it was the target for the memory-guided saccade task. Immediate presaccadic activity did not distinguish between a saccade to the receptive field when there was no distractor and a distractor in the receptive field when the monkey made a saccade elsewhere. Nonetheless the distractor had no significant effect on the saccade latency, accuracy, or v elocity despite the brisk response it evoked immediately before the saccade . We suggest that these results are inconsistent with a role for LIP in the specific generation of saccades, but they are consistent with a role for L IP in the generation of visual attention.