On the importance of the transient visual response in the superior colliculus.

A salient event in the environment can initiate a complex orienting response that includes a shift in gaze. The midbrain superior colliculus (SC) contains the appropriate circuitry to generate and distribute a signal of the priority of this event, and co-ordinate the orienting response. The magnitude and timing of the short-latency transient visual response in the SC, when combined with cortical inputs signaling stimulus relevance and expectation, influences the type and latency of the orienting response. This signal in the SC is distributed to higher cortical areas to influence visual processing, to the reinforcement learning system to influence future actions, and to premotor circuits, including neck and shoulder muscles, to influence immediate action.