Week 4. Is BR the best method of studying consciousness?
– Binocular rivalry, such a department store for studying consciousness –
Hunjae Lee (VCC Lab)
Outside of a laboratory, it is hard to experience binocular rivalry (BR). With two eyes those are looking almost similar images in the same line of sight we aware a sole and stable image in usual life. However, for no other reason but binocular rivalry cannot be underestimated which is like a department store reflecting various phenomena of consciousness, including transience of visual awareness despite of same physical stimuli, attention effects on consciousness, the problem of top-down versus bottom-up, locus of consciousness and so on. BR brings us many crucial points to contemplate.
Wrapping up many studies till now, there are reliable evidences that BR cannot be fully explained by interocular competition between monocular neurons in early visual cortex. Both single cells recorded from monkeys (Logothetis, N. K. et al, 1989; Leopold, D. A. et al, 1996) and many neuroimaging evidences from human (mentioned in Tong et al, 2006) indicate that there are more mechanisms reflecting and modulating subjective perception during the BR. From those researches, it seems convincing that BR arises through interactions among binocular neurons at several levels in visual pathways (Leopold, D. A. et al, 1996).
And here comes attention again. During BR, attention which is a sort of the high-level excitatory influence can extend the local dominance of a stimulus over space and time (Tong et al, 2006). Furthermore Lee, S. H. et al (2007) found differential effects of attention on traveling waves in different visual cortex, such as V2, V3 but V1 importantly. This is outstanding that we stepped forward to clarify something about interaction between the top-down and the bottom up processing which is too general and ambiguous.
Despite of abundant previous findings, lots of questions still remain answered. For example, to what extent does BR share common mechanism with other multi-stable perception? Is perceptual alternation during the BR related to neuronal oscillation? One recent article provides that perceptual switching during the BR is time-locked to gamma-band synchronizations that recur at a theta rate, indicating the onset of new conscious percepts coincides with the emergence of the new gamma-synchronous assembly (Doesburg, S.M. et al, 2009).
In summary, using the BR method in studying consciousness revealed many aspects of dynamic visual awareness and is ongoing as ever, raising prominent questions. In addition, BR takes advantages in analyzing multiple stages of perception and its’ dramatic changing with attention, that make BR convenient to study even animals, which is crucial to investigate neural mechanisms of consciousness. It is hard to choose other method instead of BR.
References
Logothetis, N. K., & Schall, J. D. (1989). Neuronal correlates of visual perception. Science, 245, 761-763.
Leopold, D. A., & Logothetis, N. K. (1996). Activity changes in early visual cortex reflect monkeys percepts during binocular rivalry. Nature, 379, 549-553.
Leopold, D. A., & Logothetis, N. K. (1999). Multistable phenomena: changing views in perception. Trends in Cognitive Sciences, 3, 254-264.
Tong et al. (2006). Neural basis of binocular rivalry. Trends in Cognitive Sciences, 10, 502-511.
Lee, S. H., R. Blake, et al. (2007). Hierarchy of cortical responses underlying binocular rivalry. Nature Neuroscience 10(8): 1048-1054.
Doesburg, S.M., Green, J.J., McDonald, J.J., Ward, L.M. (2009). Rhythms of Consciousness: Binocular Rivalry Reveals Large-Scale Oscillatory Network Dynamics Mediating Visual Perception. PLoS ONE 4(7): e6142.