Sampling and Optimal Cue Combination during Bistable Perception

Field: Neuroscience (Life Sciences)

Event Abstract Back to Event Sampling and Optimal Cue Combination during Bistable Perception When looking at a moving ball, psychophysics experiments suggest that we represent all directions, along with their probabilities, even though we appear to perceive only one direction. This type of probabilistic representations allows behavior to be optimal given the uncertainty inherent to our sensory stimuli. But if the brain represents multiple interpretations in the form of probability distributions, why do we get a sense of unitary perception? Is this a mere illusion or the result of an active process, such as sampling, that collapses probability distributions onto single interpretations? In this study, we take advantage of bistable perception and cue combination to explore the possibility that perception is the result of a sampling process. The Necker cube is a well known example of a bistable percept. In this case, perception is unitary (only one interpretation of the Necker cube is perceived at any given time), but it is bistable, in the sense that the interpretation changes from time to time. The source of this bistability is not fully understood, although it has been proposed to arise from a sampling process of a bimodal probability distribution which peaks sharply at the two interpretations of the stimulus. To test this idea, we employed a stimulus made of two superimposed drifting gratings, which is ambiguous as to which grating is moving in front and which one is moving behind. By varying the spatial frequency, the speed or disparity of one grating, it is possible to bias in a gradual manner the fraction of time that a particular grating is perceived as being in front. We asked subjects to report the spontaneous alternations in depth ordering over a one minute period, and measured the fraction of dominance time f for each percept. The key question is how the perceived depth ordering changes when two cues (e.g. spatial frequency and speed) are varied simultaneously. If the brain combines the two cues optimally, the probability distribution over depth ordering given both cues should be the product of the probability distributions given each cue separately. Moreover, if the brain samples this posterior distribution (or any arbitrary power of it), then the fraction of dominance of a particular depth ordering when two cues are manipulated simultaneously should follow f1,2 = f1 f2 / ( f1 f2 + (1- f1) (1- f2) ), where f1 (resp. f2) is the fraction of dominance of one particular depth ordering when cue 1 (resp. cue 2) is manipulated alone We report that the experimental confirms this prediction, and cannot be described by other candidate models, such a cue vetoing or “stronger-cue-take-all” strategies. Finally, we show that a simple neural model is able to account for this behavior as long as neurons simply sum their inputs. Interestingly, a simple sum is also the combination rule that ensures optimal cue combination given the statistics of spike trains in the cortex. Therefore, bistable perception appears to be the result of a sampling process of the posterior distributions obtained from optimal cue integration. Conference: Computational and systems neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009. Presentation Type: Poster Presentation Topic: Poster Presentations Citation: (2009). Sampling and Optimal Cue Combination during Bistable Perception. Front. Syst. Neurosci. Conference Abstract: Computational and systems neuroscience 2009. doi: 10.3389/conf.neuro.06.2009.03.098 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 02 Feb 2009; Published Online: 02 Feb 2009. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Google Google Scholar PubMed Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.