Principal Investigator: Shih-Cheng Yen
Cortical Basis of Perceptual Salience
One of the central problems of cognitive neuroscience is to understand the link between cortical activity and perception. This is illustrated in vision, where one of the unresolved questions, commonly referred to as the binding problem, concerns how different cortical areas, which are specialized for processing, different visual features in parallel, arc integrated into a coherent percept. Over the last decade, the hypothesis has arisen that synchronization of cortical activity may represent a possible solution to this problem. The hypothesis remains controversial, with theoretical and experimental evidence in support and opposition. Despite several exciting recent findings, the definitive experiment remains to be done.
In my Ph.D. dissertation, I proposed a link between neuronal synchronization and perceptual salience which I believe may provide the theoretical basis for the critical experiment on the functional significance of neuronal synchronization. The Gestalt psychologists at the turn of the century proposed a number of rules that described the salience of different perceptual groupings and different figure-ground segregation, and since then, the challenge has been to identify the aspects of neural firing patterns (e.g. firing rates, synchronization, etc.) that mediate these percepts. I developed a cortically based network model, made up of detailed compartmental models of pyramidal cells and interneurons, that argues for the hypothesis that the organization of features is mediated by the architecture of intra-cortical connections while the salience is represented by the sum of synchronized activity in the underlying population of cells. We were able to show that changes in synchronization accounted for changes in perceptual performance, and that failure to synchronize led to errors in performance. The model was tested in a large range of simulations, and shown to account for a comprehensive set of psychophysical experiments on contour salience.
The model makes several key predictions about the relationship between
perceptual salience, neuronal synchronization, and behavioral performance.
I propose to experimentally test these predictions in the laboratory of
Dr. Charles Gray at UC Davis. We will use awake, behaving monkeys to obtain
behavioral measures that can be correlated with the synchronization of
neuronal activity. In our experiments, we will use visual stimuli that
have been extensively studied in human psychophysical experiments in order
to better relate the animal's behavior to human perception. Multiple single
unit recordings will be carried out in area 17 of the macaque using the
new tetrode recording technique, developed by Dr. Gray and his colleagues,
while the animals perform the perceptual task. We believe the results
of the experiments will provide definitive evidence to either confirm
or reject the functional significance of neuronal synchronization, and
provide insights into the neural architecture and circuitry that allows
the brain to effectively solve the binding problem.
