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Yulia Lerner, Miki Fukui, Nava Rubin; Bi-stable perception and neural competition at equidominance and away from it. Journal of Vision 2008;8(6):251. doi: 10.1167/8.6.251.
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© ARVO (1962-2015); The Authors (2016-present)
When a stimulus supports two distinct interpretations, perception alternates haphazardly between them. fMRI studies that revealed large concurrent changes in the activity of neural populations associated with the competing percepts used stimuli where each interpretation was dominant for roughly half the time (‘equi-dominance’). Yet, parametric stimulus modifications can change the relative strength of the competing interpretations, and consequently the fraction of time observers spend in each. What are the neural correlates of such changes in the ‘balance of powers’?
We recorded fMRI activity while observers viewed moving plaids - which produce alternations between the perception of a single moving surface (‘coherency’) and two gratings sliding over each other (‘transparency”) - and continually indicated their perception. By varying the angle between the directions of motion of the constituent gratings we controlled the relative strength of the two interpretations. Three different values yielded displays that gave rise to a ‘transparent’ percept 25%, 50%, and 75% of the time, in separate runs of 5 min each.
Similarly to findings in other bi-stability domains, at equi-dominance, marked anti-phase activity changes locked to perceptual alternations were found in early visual cortex: increases in the V1–V3 and KO during coherency and in the right LO during transparency. Surprisingly, away from equi-dominance (at 25% and 75% transparency) voxel-by-voxel analysis did not reveal activity changes in the same early visual areas during perceptual alternations; ROI analysis showed only modest changes. By contrast, more anterior cortical regions showed strong perceptually-related modulations in all cases. Away from equi-dominance, activity rose during perception of the weaker interpretation in the right STS and bilaterally around the IPS and PCS. At equi-dominance, activity rose in extensive regions in the anterior lef- and right-hemispheres during perception of the stronger and weaker interpretations, respectively. Neural correlates of perceptual competition therefore differ at equi-dominance and away from it.
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