Perceptual and motor mechanisms of oculomotor inhibition of return

We propose and simulate, with a dynamic neural field model, two mechanisms underlying inhibition of return (IOR) in the oculomotor system: sensory and motor. Reflecting sensory adaptation (or habituation) repeated visual stimulation results in a reduction of visual input to the superior colliculus (SC); consequently, saccades to targets which appear at previously stimulated locations will have longer latencies than those which appear at unstimulated locations. In contrast, the execution of a saccade results in asymmetric activation in the SC; consequently, saccades which reverse vectors will have longer latencies than those which repeat vectors. In the IOR literature, these two mechanisms correspond to IOR effects observed following covert exogenous orienting and overt orienting in the absence of peripheral stimulation, respectively. We predict that these two independent mechanisms will have additive effects; a prediction that is confirmed in a behavioral experiment.