Neurophysiology of Visual Perception

National Institute Of Mental Health

Investigators

Linked publications & trials

Abstract

Human cognition is strongly connected to our advanced visual capacities, which allow us to make detailed observations of the world, its objects, spatial layout, and one another. Vision forms the foundation for much of our thinking, our memory, and our language. Our research program investigates the brain mechanisms underlying how we see objects, scenes, and individuals. Historically, the investigation of vision has derived from experiments in which stimuli are presented alone on a screen. This isolate presentation of simplified stimuli allows for the evaluation of how brain areas are specialized for certain types of visual patterns. This approach has led to a standard view of the visual brain that is hierarchical and modular. In this framework, a specific visual percept is assumed to emerge from the selective activation of some brain areas over others. An important question, however, is whether this framework extends to more natural modes of vision, where the visual environment is complex, immersive, and temporally continuous. Much of our work over the last year has attempted to understand how the brain contends with its everyday visual input. In one project, we have investigated whether there is a fundamental difference between continual visual experience, as for example experienced while watching a video, and the discrete stimulation of the brain that forms the basis of most visual neuroscience experiments. In our experiments, we have allowed subjects to freely view natural movies that play out over several minutes, record their gaze and brain activity during this time. This study, currently under revision, revealed that the temporal context critically shapes how visual details are processed. For example, movie content presented discretely in brief snippets and out of order elicits wholly different responses from the brain compared to the same content presented in its original continuous movie context. In another project we are investigating the 3D nature of vision as it pertains to the brains encoding of objects. In contrast to most studies of object encoding, which emphasize the brains tolerance to different spatial transformations, we demonstrate that object-selective neurons are highly sensitive to natural visual geometry. Our findings demonstrate that the size variable affecting the tuning object selective neurons is not the angle cast on the retina, but instead the absolute size of objects in centimeters. This finding has implications for the nature of visual representations in the brain. In a final project, we have been investigating the nature of high-level visual memory in the ventral visual cortex of the brain. By tracking individual neurons across days and weeks, we found that the familiarity of objects impacts a population of neurons only gradually. Careful examination revealed that the division of labor in the neural population broke down by the rate of learning. Namely, some neurons showed signs of familiarity rather soon after new stimuli were introduced, within 2-3 days, whereas other neurons started to alter their responses much later, only after a few weeks. Within the population, this cascade of plasticity may link to the graded and continuous intensity of familiarity that accompanies exposure to stimuli.