Kinsey, K., Anderson, S., Hadjipapas, A. and Holliday, I.
The role of oscillatory brain activity in object processing and figure–ground segmentation in human vision.
International Journal of Psychophysiology.
Available from: http://eprints.uwe.ac.uk/13886
Publisher's URL: http://dx.doi.org/10.1016/j.ijpsycho.2010.12.007
The perception of an object as a single entity within a visual scene requires that its features are bound together
and segregated from the background and/or other objects. Here, we used magnetoencephalography (MEG) to
assess the hypothesis that coherent percepts may arise from the synchronized high frequency (gamma)
activity between neurons that code features of the same object. We also assessed the role of low frequency
(alpha, beta) activity in object processing. The target stimulus (i.e. object) was a small patch of a concentric
grating of 3 c/°, viewed eccentrically. The background stimulus was either a blank field or a concentric grating
of 3 c/° periodicity, viewed centrally. With patterned backgrounds, the target stimulus emerged – through
rotation about its own centre – as a circular subsection of the background. Data were acquired using a 275-
channel whole-head MEG system and analyzed using Synthetic Aperture Magnetometry (SAM), which allows
one to generate images of task-related cortical oscillatory power changes within specific frequency bands.
Significant oscillatory activity across a broad range of frequencies was evident at the V1/V2 border, and
subsequent analyses were based on a virtual electrode at this location. When the target was presented in
isolation, we observed that: (i) contralateral stimulation yielded a sustained power increase in gamma
activity; and (ii) both contra- and ipsilateral stimulation yielded near identical transient power changes in
alpha (and beta) activity. When the target was presented against a patterned background, we observed that:
(i) contralateral stimulation yielded an increase in high-gamma (N55 Hz) power together with a decrease in
low-gamma (40–55 Hz) power; and (ii) both contra- and ipsilateral stimulation yielded a transient decrease
in alpha (and beta) activity, though the reduction tended to be greatest for contralateral stimulation. The
opposing power changes across different regions of the gamma spectrum with ‘figure/ground’ stimulation
suggest a possible dual role for gamma rhythms in visual object coding, and provide general support of the
binding-by-synchronization hypothesis. As the power changes in alpha and beta activity were largely
independent of the spatial location of the target, however, we conclude that their role in object processing
may relate principally to changes in visual attention.
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