|Reference code: ||PT/FB/BL-2014-373.03|
|Binding of ambiguous visual stimuli is associated with changes in beta power but not with synchrony|
|Publication year: ||2016|
In vision, perceptual features are processed in several regions distributed across the brain. Yet the brain achieves a coherent perception of visual scenes and objects through integration of features that are encoded in spatially segregated brain areas. How the brain seamlessly achieves this accurate integration is currently unknown and is referred to as the "binding problem" (Von der Malsburg, 1981). Among the proposed mechanisms meant to resolve the binding problem, the binding-by-synchrony hypothesis (BBS) proposes that binding is carried out through the synchronous discharge of different neuronal assemblies (Singer & Gray, 1995). The present study aimed at providing a critical test to the BBS hypothesis by evaluating long range connectivity during a motion integration visual task that entails binding across hemispheres.
EEG (58 channels) was recorded while participants observed an ambiguous stimulus that could be perceived in either a "bound" configuration, requiring visual integration across hemispheres, or an "unbound" configuration, where the images at each hemifield were perceived as being separate (Wallach, 1935; English translation in Wuerger et al., 1996). Participants reported continuously their perceptual decision. 21 subjects performed this task.
Synchrony between neural populations belonging to distinct hemispheres was estimated using the imaginary part of coherency (ImCoh) in search of a correlation between interhemispheric synchrony and perceptual binding. We found no evidence of increased synchrony during periods of bound perception, compared to unbound, at alpha (8-12 Hz), beta (13-30 Hz) or gamma frequencies (> 30 Hz) and perceptual changes were not accompanied by changes in ImCoh. The distinct visual experiences showed, nonetheless, differences in power, particularly at the beta frequency range (12-23 Hz) over parietal regions. Moreover, around the moment of perceptual switches, changes in alpha and beta power provided clear neurophysiological correlates of a change in visual experience, with an increase in beta oscillations indicating a change towards a bound configuration.
Our findings reveal that the visual experience of binding can be identified by distinct signatures of oscillatory activity, regardless of long range synchrony. In our current paradigm, visual binding occurred under ambiguous conditions, but integration of visual information across hemifields was found not to correlate with increased synchrony across hemispheres. On the other hand, spectral signatures of increased power at beta frequencies were found to correlate with the perception of the bound stimulus. When the bound configuration was the dominant percept, beta activity was increased compared to the unbound perception, with greater differences found over parietal regions. This suggests that the ambiguity might be resolved at hierarchically higher cortical areas without the need for synchronous activity at lower visual ones.
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|Secondary author(s): |
|Duarte, J., Martins, R., Castelo-Branco, M.|
|Document type: |
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|Costa, G., Duarte, J., Martins, R., & Castelo-Branco, M. (2016, June). Binding of ambiguous visual stimuli is associated with changes in beta power but not with synchrony. Poster presented at the 22nd Annual Meeting of the Organization for Human Brain Mapping, Geneve, Switzwerland. Abstract retrieved at https://ww5.aievolution.com/hbm1601/index.cfm?do=abs.viewAbs&abs=2992|
|Indexed document: ||No|
|Keywords: ||Electroencephalogram (EEG) / Vision / Binding / Synchrony / Oscillations|