This is a proposal to renew funding for research using a novel approach - measuring the dynamics of perceptual bi-stability in ambiguous motion displays - to study the mechanisms underlying motion integration and segmentation. This problem is central to motion processing, and it can also be used as a model for how the brain computes a global percept from many isolated local cues in other domains of vision. There has been previous research on this topic using brief-presentation methods. Our approach focuses on the dynamics of perceptual alternations during long presentations of ambiguous motion displays. In the first phase of the project we showed that dynamics-based measures are sensitive to stimulus manipulations in wide parametric ranges, including where brief-presentation methods suffer from """"""""ceiling"""""""" and """"""""floor"""""""" effects. With this methodological advantage we have uncovered a wealth of new and unsuspected findings about plaid perception. We have also adapted the dynamics methods to the fMRI environment, and identified two localized cortical sub-regions, labeled KOint and LOseg, whose activation is strongly correlated with the perceptual dominance durations of the alternating percepts. Activity in these two regions is in anti-phase, crossing-over with perceptual switches. In the proposed continuation phase of the project we will (i) provide further support for the hypothesis that the perception of the ambiguous plaid stimulus is determined by the outcome of competition between the two occipital regions we have identified, KOint (associated with motion integration) and LOseg (motion segmentation), (ii) test that the behavior exhibited by LOseg and KOint is not specific just for the plaid, but rather generalizes also to other ambiguous stimuli that involve competition between motion integration and segmentation, (iii) test a complementary prediction that is also implied by our hypothesis that LOseg and KOint mediate competition between motion segmentation and integration, namely that these two regions should not exhibit anti-phase modulations when observers undergo perceptual alternations caused by ambiguous motion displays that do not involve integration/segmentation competition, (iv) further elucidate the role of LOseg and KOint in motion-based segmentation and integration compared with form-based segmentation and integration, (v) generalize our results to more complex stimuli, specifically stimuli that require different global motion processing in different portions of the visual field.
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