Probing the prerequisites for motion blindness

Neurobiological studies of visual awareness usually focus on the neural events elicited by perceived or nonperceived stimuli but neglect the preexisting conditions that allow ( or prevent) conscious perception. We have examined the conditions that lead to temporary motion blindness in a rapid serial visual presentation paradigm, in which subjects have to detect coherent motion in the peripheral stream after a cue ( a red fixation point) in the central stream. The failure of awareness depends critically on the occurrence of similar coherent motion events ( probes) before the cue. Event-related brain potentials (ERPs) were recorded to track the processing of motion distractors, which determine the prerequisites for this transient deficit. Analysis of motion-evoked responses revealed that there is no progressive reduction in sensitivity in early visual processing. There is, however, a progressive increase in amplitude of a negative wave over the frontal cortex at approximately 250 msec after motion onset and a corresponding reduction of a centro-parietal positivity at approximately 350 msec with an increasing number of distractors. We propose that these nonsensory ERP components reflect a postperceptual frontal gating mechanism that controls the access of visual stimuli to higher order evaluation and conscious detection.