Abstract
We have previously reported a paradigm in which attentional capacity was modulated in the temporal domain by using two synchronised rapid serial visual presentation (RSVP) streams. A red fixation in one stream was the ‘cue’ to switch attention to the surrounding global stream. This switch between streams evoked a transient deficit in visual motion perception (Sahraie et al, 2001 Vis Res 41, 1613–7) and in detection of a change in disparity (Sahraie et al. 2003 VSS). The recovery functions for detection of both features (motion & disparity) following the cue onset were similar (< 300ms). For both motion and disparity, the detection impairment was most severe when irrelevant motion or disparity changes (distractors) occurred prior to the cue onset. Therefore, we have proposed that the impairment was due to the active suppression of the distractor events by top-down mechanisms. The time-course of the recovery would reflect the gating of information to higher-order stimulus evaluation (or controlled stimulus processing). Further support for this suppression hypothesis was obtained in our electrophysiological studies (Niedeggen et al. J. Cogn. Neuro, in press). Here we report on the effect of distractors in activating the suppression mechanism for motion and disparity distractor events. Each subject (n=10) carried out two experiments, a motion discrimination and a detection of disparity. In each experiment the percentage of distractor events prior to the local cue varied between 0, 20 and 80%. The results indicated that for both motion and disparity detection, performance at cue-target SOA 0 and 100ms deteriorated with increasing number of distractors. Furthermore, the extent of the deterioration was similar for motion and disparity, which may indicate that both disparity and motion are equally affected by the top-down modulation. We propose that the suppression of distractor stimuli is a general effect which takes place at a central rather than sensory level.
Research was supported by a grant from the VolkswagenStiftung (VW 2277)