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Abstract:
Abstract: Processing of visual information occurs in a
spatially distributed and highly parallel manner. The mechanisms
mediating binding of distributed activity for further processing
are largely unknown. Psychophysical experiments have revealed that
feature binding can critically be influenced by temporal aspects
like synchronous vs. asynchronous flickering of visual elements.
Here, we explore the mechanisms underlying this phenomenon.
Multiunit-activity and local field potentials were recorded from
areas 17/18 of visual cortex in anesthetized cats. Neurons were
stimulated by drifting and/or flickering sinusoidal gratings
presented on a computer screen (frame rate 160Hz). In both cortical
areas, neurons showed phase-locking to flicker frequencies of up to
80 Hz. Discharges occurred at frequencies corresponding to the
stimulation frequency and several additional harmonics. Moreover,
responses to high- and low-frequency flicker were state-dependent.
At states distinguished by low frequencies in the ongoing field
potential the cortex followed predominantly flicker stimulation at
lower frequencies. However, in epochs characterized by high
frequency spectral components cells were able to phase-lock to fast
stimulus flicker. Finally, externally driven oscillations could
coexist with internally generated synchronization among separate
neurons. Whereas the former arose from phase-locking to stimulus
flicker, the latter was induced by the coherent drift of stimulus
contours. The findings are compatible with the notion that external
temporal cues can influence cortical binding operations implemented
by timing of neuronal discharges.
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