We are interested in the neural correlates of human visual perception. We make use of a relatively new technique for measuring brain responses in humans called Functional Magnetic Resonance Imaging or fMRI. This technique uses a standard clinical MRI scanner to measure changes in the blood flow and oxygenation of the vasculature in the brain that correlate with neuronal responses. Our laboratory uses fMRI to determine where and how the brain responds by making fMRI measurements in the visual cortex of human observers while they view various visual stimuli.
Some of my previous work as a postdoctoral fellow at Stanford University involved studying brain responses in people with developmental dyslexia. We found that those with developmental dyslexia showed lower fMRI responses than control subjects in a motion processing area of the brain, called area MT+, and that these differences correlate well with behavioral measurements using a speed discrimination task. These results are consistent with the hypothesis that developmental dyslexia is associated with a defecit in the magnocellular pathway of the visual system.
Our current research includes studying the effects of spatial and feature-based attention on responses in early visual areas. Until recently, it was believed that the first stages of visual processing (in humans and other primates) operate in a passive, feed-forward manner that is independent of the attentional state of the observer. However, using fMRI, we discovered that directing both spatial and feature-based attention to specific parts of the visual field can modulate responses as early as in the primary visual cortex. This discovery requires us to think differently about the nature of the neural circuitry in the early stages of human vision.
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