This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We have made progress on Specific Aims 1 and 4 of the proposed project: Compare responses of MT cells to global stimuli with predictions based on the properties of the cell s average input. We did these experiments and found that we could predict responses of MT cells to fast and moderate speed stimuli, but not the slow stimuli. This indicates a non-linear or rectified suppression at slow speeds. This suppression is apparent as a delayed non-directional suppression in the interaction maps. This work has been written up and submitted for publication. We also began looking at the contrast dependence of speed tuning in MT cells, and realized that the time-course of the response as a function of contrast might explain the powerful motion illusion discovered by Akiyoshi Kitaoka. We did find in both V1 and MT a correlation between responses to static pair of bars and the motion illusion. This work was recently published in J. Neurosci. Explore the role of end-stopping in extracting the correct direction of global motion: Motion direction along extended contours is locally ambiguous, so the most accurate information about an object s true direction of motion is at its corners or ends. We propose to ask whether MT cells ability to extract the true direction of object motion is correlated with end-stopping in its local-motion detectors or to a more complicated calculation that weights the relative contributions of end-stopped and non-end-stopped inputs. We began these experiments and found that end stopping does appear to be correlated with the ability to resolve the correct direction of motion.
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