Cox, Dustin

A thorough delineation of the extent of processing possible without visual awareness is necessary to elucidate the neural mechanisms of visual awareness. Despite extensive research, it is presently unclear whether invisible stimuli can undergo advanced processing. To introduce existing work on this topic, previous behavioral efforts to investigate the extent of processing possible without visual awareness and the psychophysical methods used to render stimuli invisible, such as visual masking and interocular suppression-based techniques, are discussed. Physiological evidence that provide support for and against the possibility that advanced information processing can occur without visual awareness are addressed. The basics of multivariate pattern classification techniques are outlined. The potential of using multivariate pattern classification analyses in conjunction with neuroimaging in the temporal domain to investigate whether advanced processing can occur without visual awareness is discussed. An original study using electroencephalography (EEG) and pattern classification techniques to investigate the extent of processing possible without visual awareness is outlined. The results of the analyses reveal that a pattern classifier did not extract neural signatures of categorical processing from EEG recordings when participants viewed an image that remained invisible for the duration of its presentation. In contrast, the results from a second experiment reveal that the pattern classifier was able to decode the category of invisible images from the EEG time series when the images would eventually become visible. The results provide support for the idea that under certain circumstances, such as when the depth of interocular suppression is reduced, advanced processing for invisible stimuli can occur.

In the present study, it was examined whether the spatiotemporal dynamics of
transitions towards target dominance in motion-induced blindness (MIB) were wave-like,
similar to those in binocular rivalry. The spatiotemporal dynamics of transitions towards
dominance in MIB were further compared with those in binocular rivalry to reveal a
potential neural locus of MIB. Across a series of experiments, the relationship between
target length, stimulus structure, presentation location and the latency for circular arc
segment-shaped targets to reappear was examined, respectively. It was found that target
reappearance durations increase with target length, as if they reappear in a gradual, wavelike
fashion. Target reappearance durations were decreased for collinear compared to
radial targets, but they were not influenced by the location of target presentation. The
results suggest MIB target reappearances are associated with traveling waves of
dominance, and early visual cortex is a likely neural substrate in which these wave-like
transitions occur.