Posterior parietal cortex automatically encodes the location of salient stimuli.

We examined the responses of neurons in posterior parietal area 7a to salient stimuli appearing alone or within multiple-stimulus displays in monkeys trained only to maintain fixation. Discharges in a population of parietal neurons encoded the location of the salient stimulus, although the latter had no task significance for the monkey. Neuronal selectivity for the location of the salient stimulus depended solely on its intrinsic difference from the background elements in the array and not on the color of the stimulus per se. These results were similar to those reported in monkeys trained to actively locate a salient stimulus in a multiple-stimulus display. A lower percentage of neurons with significant selectivity for the salient stimulus was observed in the fixation-only animals. These neurons took longer for the selective responses to emerge and showed a lower power of discrimination. The findings suggest that the posterior parietal cortex automatically detects and encodes the location of salient stimuli even when they are unrelated to the behavioral task.