The contribution of general and specific motor inhibitory sets to the so-called auditory inhibition of return

The detection of sounds that come from a region of space recently exposed to acoustic stimulation is often slower than the detection of sounds coming from regions of space previously unexposed to acoustic stimulation. The relative increase in reaction time (RT) to targets in recently stimulated locations is generally termed “inhibition of return” (IOR). This term alludes to the possibility that spatial attention is biased against returning to recently visited locations, thus favoring the sampling of new sources of information. However, auditory IOR effects found in paradigms where subjects have to detect a first sound (cue) without making an overt response to it, and then respond as fast as possible to a second sound (target), may be due to a purely motor inhibition carried over from cue to target. Such motor inhibition has been shown to be maximal when cue and target belong to the same category, such as when they occupy the same spatial position. We have assessed the possible contribution of this motor inhibition to auditory IOR effects by having subjects respond to both cues and targets randomly presented in a right location and a left location. Reaction time to targets preceded by cues at the same location was longer than reaction times to targets preceded by cues at the opposite location (IOR effect). Compared to a condition in which subjects responded only to targets, the IOR effect was smaller, but still significant, in the double response condition, suggesting that such an effect depends on both motor inhibition and other factors, possibly related to covert spatial orienting and oculomotor control. A second experiment indicated that the IOR effect component independent of motor inhibition was slightly but significantly greater when space was relevant to the task because subjects had to report the positions of both cues and targets, compared to when space was irrelevant to the task because subjects were not required to report stimulus positions.