Neurons are the fundamental processing unit in the brain; however, it is not known how neural activity leads to complex processes such as perception and behavior. By exploring the neural signals which underlie human pattern vision, the proposed experiments will test the hypothesis that these processes are mediated by the pooled activity of many neurons. The general approach used in all three experiments is to link psychophysical perception of a stimulus to the neural activity evoked by that stimulus in early visual areas as measured by fMRI. In the first experiment, the neural basis of pattern masking is explored. Subjects perform a contrast discrimination task while the neural activity is measured by fMRI. The preliminary data reported in this proposal show that under stimulus conditions which produce masking, the neural responses to the target are suppressed. Further analysis will be done on this data and on data from additional subjects by simultaneously fitting the psychophysical and fMRI data with a response normalization function with several decision rules to try to identify which information is pooled in a pattern detection task.
The second aim expands on the results of the firsts. Patterns can be masked by stimuli which occur asynchronously (forward masking). In the third the experiments are extended to look outside V1 and show that neural signals code for perceptual experience and not physical features of a stimulus in a texture discrimination task.
