TO INFEROTEMPORAL NEURONS THE WHOLE IS NOT THE SUM OF THE PARTSHare, Erin (2017) TO INFEROTEMPORAL NEURONS THE WHOLE IS NOT THE SUM OF THE PARTS. Doctoral Dissertation, University of Pittsburgh. (Unpublished) This is the latest version of this item.
AbstractVision seems to occur effortlessly and without mistakes. As a result, it is easy to lose sight of the complex representational mechanisms going on under the hood. In macaque monkeys, the brain region thought to be the ultimate mediator of object recognition is the inferotemporal cortex (IT). The purpose of this dissertation was to investigate how IT neurons handle parts of objects, both in a context wherein parts interfere with one another as well as a context in which certain parts aren’t readily perceived. We broke this down into three distinct projects, outlined below. The first project was concerned with the behavioral phenomenon known as crowding, in which clutter causes peripheral objects to devolve into an unintelligible jumble. We are the first to develop a task that was conducive to concurrent behavior and neuronal recordings in monkeys. To demonstrate relevance of our task, we turned to a hallmark of crowding: that what matters is the eccentricity and spacing between objects, not object size. Having demonstrated this, we were set to proceed to neuronal recordings. Our primary question was whether crowding quantitatively reduced the strength of IT neuronal selectivity or alternatively whether crowding induced a qualitative change to the neuronal code. Our results support the latter hypothesis. We then asked additional follow-up questions regarding size-sensitivity and adjacency of part-part interactions. Overall, our results were incompatible with a pooling model of crowding and consistent with models based on attention, texture, or source confusion. The final experiment was concerned with whether certain parts of compound objects were preferentially represented over others. To do this we recorded IT spiking activity while monkeys viewed composite shapes made up of overlapping outlines, as well as all the possible constituent closed parts created by the overlap. Humans tend to only perceive the simpler shapes originally used to create the composite, but the same was not true of IT neurons. Instead, they represented the composite more like its external contour than any other part, especially in the initial phase of the response. Share
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