Inhibitory tagging both speeds and strengthens saccade target selection in the superior colliculus during visual search

It has been suggested that, during difficult visual-search tasks involving time pressure and multiple saccades, inhibitory tagging helps to facilitate efficient saccade target selection by inhibiting saccades to objects in the scene once they have been searched and rejected. The superior colliculus (SC) is a midbrain structure that is involved in target selection, and recent findings suggest an influence of inhibitory tagging on activity in the SC. Precisely how, and by how much, inhibitory tagging affects target selection by SC neurons, however, is unclear. The purpose of this study, therefore, was to characterize and quantify the influence of inhibitory tagging on target selection in the SC. Rhesus monkeys performed a relatively difficult visual-search task involving time pressure and multiple saccades. During the task, target selection by SC neurons was both more rapid and more robust—as quantified via shifts in selection metrics derived from temporal receiver operating characteristic analyses—when an uninspected saccade-target object was selected from among inspected, as opposed to uninspected, objects in the display. This suggests that inhibitory tagging both speeds and strengthens saccade target selection at the level of individual SC neurons. The results provide constraints on models of target selection based on SC activity.