Inhibition of return in cue-target and target-target tasks.

Inhibition of return (IOR), the term given for the slowing of a response to a target that appeared at the same location as a previously presented stimulus, has been studied with both target-target (TT; participants respond to each successive event) and cue-target (CT; participants only respond to the second of two events) tasks. Although both tasks have been used to examine the processes and characteristics of IOR, few studies have been conducted to understand if there are any differences in the processes that underlie the IOR that results from ignoring (CT paradigm) or responding to (TT paradigm) the first stimulus. The purpose of the present study was to examine the notion that IOR found in TT tasks represents "true" IOR whereas IOR found in CT tasks consist of both "true" IOR and response inhibition (Coward et al. in Exp Brain Res 155:124-128, 2004). Consistent with the pattern of effects found by Coward et al. (Exp Brain Res 155:124-128, 2004), IOR was larger in the CT task than in the TT task when a single detection response was required (Experiment 1). However, when participants completed one of two spatially-directed responses (rapid aiming movement to the location of the target stimulus), IOR effects from the CT and TT tasks were equal in magnitude (Experiment 2). Rather than CT tasks having an additional response inhibition component, these results suggest that TT tasks may show less of an inhibitory effect because of a facilitatory response repetition effect.