Sensory and motor mechanisms of oculomotor inhibition of return.

We propose two explicit mechanisms contributing to oculomotor inhibition of return (IOR): sensory and motor. Sensory mechanism: repeated visual stimulation results in a reduction in visual input to the superior colliculus (SC); consequently, saccades to targets that appear at previously stimulated retinotopic locations will have longer latencies than those that appear at unstimulated locations. Motor mechanism: the execution of a saccade results in asymmetric activation in the SC; as a result, saccades that reverse vectors will have longer latencies than those that repeat vectors. In the IOR literature, these two mechanisms correspond to IOR effects observed following covert exogenous orienting and overt endogenous orienting, respectively. We predict that these two independent mechanisms will have additive effects, a prediction that is confirmed in a behavioral experiment. We then discuss how our theory and findings relate to the oculomotor IOR literature.