Transient blindness to disparity defined depth

Background: We have devised a paradigm to modulate selective attention in temporal domain using two synchronised rapid serial visual presentation (RSVP) streams (features: colour and motion). A switch between the streams evoked a transient deficit in visual motion perception (Sahraie et al, 2001, Vis Res. 41, 1613-7). Purpose: We have investigated whether disparity defined depth can also be modulated by attention using a similar paradigm. Methods: Subjects viewed two synchronised RSVP streams. A local stream was defined by a fixation point changing colour every 100ms , and provided a 'cue' with the onset of a unique red fixation. A global stream consisted of a static black/white random noise with and an annulus surrounding the fixation that appeared in a different depth plane (baseline plane) with respect to the background. The disparity of annulus could be temporally modulated every 100ms but transient disparity changes preceding the onset of the colour cue (distractors) were to be ignored. Following the cue onset, subjects' task was the detection of a transient disparity defined change in depth of the annulus (target) appearing in a plane either in front or behind the baseline plane. Stimulus onset asynchrony (SOA) of cue and target was varied between 0, 100, 300 or 500 ms. In the control condition, subjects were asked to ignore the fixation colour changes and report the last transient change in depth plane. Results: At 0ms SOA, subjects were at chance level in detecting a transient change in disparity defined depth. Performance improved at longer SOAs (>90% at 500ms SOA). Subjects were not impaired in detecting the depth target if its onset was not preceded by distractors, or in the control condition. Conclusions: Similar to motion detection, a change in disparity defined depth is also modulated by attentional demands. The 'distractor effect' obtained for both features probably reflects a top-down regulation which parallels recent neurophysiological findings.