A critical role for endogenous processes in inhibition of return

Response time to visual targets at peripheral locations can be delayed if the target location was previously cued, a phenomenon called inhibition of return (IOR). Given that IOR is found under what are assumed to be conditions of exogenous (reflexive), but not endogenous (volitional) covert attentional orienting, it is accepted that the IOR effect is the result of a cognitive mechanism that operates at an exogenous, stimulus-driven level. The cue in a classic IOR target detection task does, however, have a predictable temporal relationship with the target, which is evidenced by a foreperiod effect - decreasing RTs with increasing cue-target interval. Thus, whether or not the endogenous attentional system plays a role in the IOR effect remains unclear. The present study tested whether endogenous attentional mechanisms play a role in IOR by systematically decreasing the utility of the cue for preparing for target onset. This was achieved by presenting trials in which peripheral cues were not followed by targets (false alarms) on 0%, 5% or 25% of trials. Overall cue-target contingency was controlled by presenting trials without a peripheral cue preceding the target (misses) on 5% or 25% of trials. By eliminating the temporal utility of the cue, and thus removing a component of endogenous preparation, the IOR effect was attenuated, but not eliminated. The results suggest, contrary to widespread assumptions, that IOR is not solely an exogenous phenomenon, but is sensitive to contributions from endogenous mechanisms. The nature of this endogenous component of IOR is discussed with respect to existing literature as well as the current findings.Arts, Faculty ofPsychology, Department ofGraduat