The effect of predictable refixation on inhibition of return
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Inhibition of Return (IOR) refers to slowed responding to stimuli appearing at recently attended locations, and it has been reported for simple detection responses but also saccadic eye movements and even reaching movements (Klein, 2000). Most research studying IOR for consecutive saccades has utilized a task structure requiring a predictable refixation between the saccade creating IOR and the one seeking to reveal it (Taylor and Klein, 2000). Predictable refixation is unlike natural visual searching, so the present study sought to determine if IOR is modified or indeed dependent upon the predictability of refixation events. Participants made sequences of three saccades beginning from the center of a horizontal seven-target array in four conditions. In all conditions, the directions of the first and third saccades were unpredictable (left or right), but in separate blocks of trials the second saccade either predictably returned to the central target location (predictable conditions; all trials matched the classical refixation sequence) or unpredictably signaled a leftward or rightward saccade (unpredictable conditions; 50% of saccade sequences randomly matched the classical refixation sequence). Also in separate blocks of trials, saccade direction could be signaled by peripheral target onsets (exogenous conditions) or arrows located at the currently fixated location (endogenous conditions). These two signal types were chosen to add an additional investigation of whether the effect of refixation varied by modality (sensory or motor). Predictability and stimulus type were crossed with each other to create four experimental conditions. In order to compare equivalent events between conditions, IOR was assessed only for sequences involving refixation and was calculated as reaction time for the final saccade as a function of its direction relative to the first saccade (same direction versus opposite direction). Significant IOR was observed in all conditions except the condition with unpredictable refixation directed by centrally presented arrows. These results indicate that response predictability is a key component of the IOR phenomenon for saccades driven by endogenous signals, but not for saccades driven by peripheral stimulus events. This adds to a growing body of evidence suggesting that IOR arises from different mechanisms depending upon how responses are elicited.