Temporal windows in visual processing: "prestimulus brain state" and "poststimulus phase reset" segregate visual transients on different temporal scales.
Dynamic vision requires both stability of the current perceptual representation and sensitivity to the accumulation of sensory evidence over time. Here we study the electrophysiological signatures of this intricate balance between temporal segregation and integration in vision. Within a forward masking paradigm with short and long stimulus onset asynchronies (SOA), we manipulated the temporal overlap of the visual persistence of two successive transients. Human observers enumerated the items presented in the second target display as a measure of the informational capacity read-out from this partly temporally integrated visual percept. We observed higher β-power immediately before mask display onset in incorrect trials, in which enumeration failed due to stronger integration of mask and target visual information. This effect was timescale specific, distinguishing between segregation and integration of visual transients that were distant in time (long SOA). Conversely, for short SOA trials, mask onset evoked a stronger visual response when mask and targets were correctly segregated in time. Examination of the target-related response profile revealed the importance of an evoked α-phase reset for the segregation of those rapid visual transients. Investigating this precise mapping of the temporal relationships of visual signals onto electrophysiological responses highlights how the stream of visual information is carved up into discrete temporal windows that mediate between segregated and integrated percepts. Fragmenting the stream of visual information provides a means to stabilize perceptual events within one instant in time.
Center for Mind and Brain Sciences (CIMeC), University of Trento, Rovereto I-38068, Italy and MEG Center, University of Tübingen, Tübingen D-72076, Germany.
Andreas
A
Wutz
Nathan
N
Weisz
Christoph
C
Braun
David
D
Melcher
D000328:Adult; D001931:Brain Mapping; D005074:Evoked Potentials, Visual / Q000502:physiology; D005260:Female; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D011930:Reaction Time / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D013995:Time; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*
MEG; integration; oscillations; phase reset; segregation; visual response