Task dependent modulation of exogenous attention: effects of target duration and intervening events.

Inhibition of return (IOR) consists of slower reaction times in response to stimuli appearing at previously attended or inspected locations. The exact mechanisms underlying the effect have not yet been determined. In the present work, we manipulated two variables, target duration and intervening event (fixation cue between cue and target), through which we modulated the IOR effect as a function of task. When the target was presented until response, the presence of an intervening event made the cueing effect more negative in all tasks, although facilitation in the absence of an intervening event was only observed in discrimination and go-no-go tasks. When the target duration was 50 ms, the effect of the intervening event on cueing was also only observed for the discrimination and go-no-go tasks. Target duration had no effect at all in the discrimination task. Possible mechanisms for these modulations (detection cost and spatial selection benefit, both of which are based on cue-target integration processes) are discussed.