On the strategic modulation of the time course of facilitation and inhibition of return

In studies of exogenous attentional orienting, response times for targets a t previously cued locations are often longer than those for targets at prev iously uncued locations. This effect is known widely as inhibition of retur n (IOR). There has been debate as to whether IOR can be observed in discrim ination as well as detection tasks. The experiments reported here confirm t hat IOR can be observed when target discrimination is required and that the cue-target interval at which IOR is observed is often longer in discrimina tion than in detection tasks. The results also demonstrate that the later e mergence of IOR is related to perceptual discrimination rather than to resp onse selection differences between discrimination and detection tasks. More difficult discrimination tasks lengthen the SOA at which IOR emerges. In c ontrast, increasing task difficulty by adding a distractor to the location opposite the target shortens the SOA at which IOR emerges. Together, the re sults reveal an adaptive interaction between exogenous and endogenous atten tional systems, in which the action of the orienting (exogenous) system is modulated endogenously in accord with task demands.