Yelda Alkan¹, Aviad Ozana¹, James Bisley^1,2,3; ¹UCLA

In two-alternative forced choice decision making, activity in the lateral intraparietal area (LIP) correlates with the accumulation of evidence to a threshold for a decision that will result in a saccade to a neuron’s response field. It has been proposed that this process could explain behavior in visual search by having an accumulator at the location of each stimulus in the array. We tested this hypothesis by having animals perform a visual search task with random dot patterns as stimuli (Alkan, Mirpour & Bisley, 2022). The animal was trained to make a saccade to a target and withhold a saccade if no target was present. We used set-sizes of 1, 2 and 4, and had conditions with 100% valid attentional cues. Stationary dots were presented before motion onset to let the animals know the set-size and attentional condition. Recording from single LIP neurons, we asked whether set-size or attention affected the starting position of the accumulator, the threshold (end point of the accumulator) and the rate of accumulation. We predicted that set-size and attention would not affect the threshold, but that they would affect the starting point of the accumulator and the rate of accumulation. As expected based on previous studies, the starting point of the accumulator varied as a function of set-size (lower for higher set-sizes) and was higher in the attention conditions, and as we predicted, saccades to targets in all conditions were made when activity reached a common threshold. However, we found no evidence that accumulation rates or target detection time differed across any of the conditions. These data are consistent with the hypothesis that visual search may be driven by parallel accumulators and suggest that the differences in reaction time and behavior in all conditions was due only to the different response levels when search began.