Abstract
The orienting phenomenon known as inhibition of return (IOR) refers to a slowing of reaction times (RTs) for the detection of a target in a previously cued location, provided the stimulus onset asynchrony between the cue and target is longer than approximately 300 ms. There is general agreement that at least two forms of IOR exist, one motoric and one sensory/attentional. Previous research examining the spatial distribution of the sensory/attentional form of IOR reveals a monotonic pattern of RTs, where RTs are slowest in a previously cued location and fastest 180°opposite. In E1, this pattern is replicated and extended to a target-target task requiring consecutive eye movements to peripheral stimuli. Surprisingly however, the spatial distribution of a purely motor form of IOR has not been explored previously. In E2, using a similar target-target with central rather than peripheral stimuli, we demonstrate that the spatial distribution of the motor form of IOR can be predicted from basic neurophysiological properties of direction encoding neurons found throughout the motor system. Specifically, based on adaptation effects within directionally selective neurons that are likely to occur in our task, we predicted and observed a non-monotonic pattern of RTs: RTs for consecutive movements offset by 90°were significantly faster than those offset by both 0°and 180°. In order to compare our results with previous IOR studies, in E3 and E4 we replicate our main findings from E1 and E2 using different stimulus configurations. Taken together, our results reveal important differences between the spatial distribution of IOR when sensory/attentional and motor effects are most likely.
