Characterizing Cortical Computation in the Context of Natural Vision

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An understanding of how the brain processes visual stimuli is confounded by the complexity of the natural visual world, combined with the intricate neuronal processing that occurs within and across multiple cortical areas. Over the last few decades, substantial progress has been made by using simple laboratory stimuli, such as moving bars or dots, to develop simple descriptions of neuronal tuning to these elements. This approach has provided a reasonable functional description of lower cortical areas, but it is unlikely to be sufficient to characterize the regions of the extrastriate cortex whose responses are thought to represent elements particular to the natural visual world. Though a joint Canadian-US collaboration, this project couples new experimental approaches based on a set of complex stimuli approaching natural vision with appropriately complex models, in order to understand how neurons in successive stages of cortical processing are tuned to more natural visual features.Most previous work with natural stimuli has focused on the ventral pathway in the cortex, which is concerned with computing object shape and identity. This is an extremely challenging problem, as the dimensionality of shape space is unknown. This project focuses instead on the dorsal stream of the primate visual cortex, which is primarily identified with motion processing. The advantage of this approach is that motion, particularly that seen in natural vision, can be locally decomposed into a low-dimensional optic flow space that can be sampled using naturalistic stimuli designed for this proposal. The development of such stimuli will extend both the spatial and temporal complexity of probes to areas in the dorsal stream, while providing the necessary constraints for a novel nonlinear modeling framework that will be developed. These models will then be applied to motion stimuli derived through simulation of natural three-dimensional virtual environments, allowing the complex processing uncovered to be linked to natural visual features. Furthermore, by performing this study across successive areas comprising the dorsal hierarchy (V1, MT, and MST), this project aims to expose general principles of cortical processing, namely how higher level abstractions are derived from lower-level visual features.This project is jointly funded by Collaborative Research in Computational Neuroscience and the OISE Americas program. A companion project is being funded by the Canadian Institutes of Health Research.