Abstract
Inhibition of return (IOR) refers to a slowing of reaction times for the detection or localization of a target object presented in the same location as a previously attended cue, provided the cue-target stimulus onset asynchrony is at least 300ms. Currently, at least two forms of IOR are thought to exist: one that affects early (sensory) processes, and the other that affects late (motoric) processes. When sensory processes are inhibited, the topography of IOR is greatest at the cued location (i.e. a 0°cue-target offset) and decreases monotonically to 180°opposite. However, to date, the topography of purely motoric IOR has not been compared to IOR involving sensory inhibition. This is surprising, because one would expect sensory and motoric inhibition to occur within different neural substrates. In order to compare sensory and motoric IOR, in two separate experiments, participants made consecutive eye movements in response to either (1) peripheral onsets, when sensory inhibition is likely or (2) arrows presented at the point of fixation, when only motoric inhibition is likely. Four possible target locations were presented in each trial (marked by placeholders). When peripheral onsets were used to signal consecutive eye movements, we observed a typical pattern of IOR, where RTs were slowest at the cued location (0°), intermediate for 90°, and fastest 180° opposite. In contrast, when central arrows were used to signal consecutive eye movements, RTs were faster only when offset by 90° degrees from the initial movement. The present results reveal a difference in the topography of purely motoric IOR compared to IOR involving sensory inhibitory processes.
