Inactivation of primate superior colliculus impairs covert selection of signals for perceptual judgments.

Primates base perceptual judgments on some sensory inputs while ignoring others. The covert selection of sensory information for perception is often thought to be accomplished mostly by the cerebral cortex, whereas the overt orienting toward relevant stimuli involves various additional structures such as the superior colliculus, a subcortical region involved in the control of eye movements. Contrary to this view, we show that the superior colliculus is necessary for determining which stimuli will inform perceptual judgments, even in the absence of orienting movements. Reversible inactivation of the superior colliculus in monkeys performing a motion discrimination task caused profound inattention for stimuli in the affected visual field, but only when distracters containing counterinformative signals appeared in the unaffected field. When distracting stimuli contained no information, discrimination performance was largely unaffected. Thus, the superior colliculus is a bottleneck in the covert selection of signals for perceptual judgments.