Abstract
Recent studies report that rapid serial visual presentation (RSVP) of task-irrelevant stimuli can have significant consequences for the perception of subsequent visual targets. One explanation for this effect is that rhythmic presentation of visual objects entrains visual cortex into a phase-locked oscillatory rhythm, resulting in rapid cycles of enhanced and suppressed perception. An alternative view is that rapid visual presentation leads to rhythm-independent neural state changes in the visual system, with enhancement of processing due to a combination of stochastic resonance ("cortical awakening") and competition incited by task-irrelevant stimuli. We sought to distinguish between these theories through a series of RSVP experiments measuring single target identification. In Experiments 1 and 2, trains of task-irrelevant black letters were presented at six frequencies between 3.3 and 36 Hz, in and out-of-phase, with a final, backward-masked red target letter. Both in and out-of-phase stimulation versus a control condition facilitated 6AFC forced-choice target identification. In Experiments 3-5, task-irrelevant letters or noise patterns were presented rhythmically and non-rhythmically at 10 Hz, followed by a red target 100 ms later ("in-phase"). In every condition, stimulation resulted in improved performance compared to a control condition, with no significant differences between the rhythmic and non-rhythmic conditions. Finally, Experiment 6 tested a full range of non-harmonic RSVP frequencies and final distractor-to-target asynchrony (DTA) in a 5x5 orthogonal design (n = 80). Stimulation at frequencies 10 Hz and above led to better performance, with poorer performance at DTAs of 35 and 167 ms. No interaction between frequency and DTA was found. The current results are consistent with models of awakening and competition, but inconsistent with oscillatory entrainment models. Perceptual consequences of rapid, task-irrelevant visual stimulation appear to be determined by a combination of "awakening" of the visual system and previously known competition arising from distractors.
Meeting abstract presented at VSS 2014