Michael Silver

Research Interests

Neural correlates of human visual perception and attention

Research Summary

When attention is allocated to a particular portion of the visual field, visual perception is enhanced at that location. This is thought to occur as a result of top-down attention signals that influence the processing of visual stimuli in occipital cortical areas. We use a combination of behavioral, neuroimaging, electrophysiological, modeling, and pharmacological techniques to characterize the neural pathways involved in the control of visual attention in humans and the effects of selective attention on processing of visual stimuli.

We have discovered two cortical areas in the human parietal lobe, IPS1 and IPS2, that contain topographic maps of spatial attention and may transmit retinotopically-specific top-down signals to early visual cortex. We are currently characterizing the functional interactions between IPS1/IPS2 and occipital visual areas. Pharmacological studies in the lab have focused on the cholinergic projection from the basal forebrain to the cerebral cortex. We have found that increasing synaptic acetylcholine levels enhances top-down spatial attention as measured behaviorally, increases the magnitude of neural (fMRI) correlates of attention in the superior parietal lobule and frontal eye fields, and reduces the spatial spread of visual responses in early visual cortex. Further pharmacological studies will determine the relationship between the effects of top-down attention signals and acetylcholine release on visual perception and on information processing in visual cortex. We are also studying the neural substrates of perceptual learning and the modulation of perceptual learning by cholinergic enhancement.

Another focus of the lab is binocular rivalry, a phenomenon that occurs when two incompatible images are presented to the two eyes. Even though the visual stimuli remain constant, visual perception alternates between the two monocular stimuli. Binocular rivalry is therefore extremely useful for understanding mechanisms underlying the selection of visual inputs for perception. Binocular rivalry projects in the lab include investigation of the effects of voluntary attention and pharmacological manipulations on perceptual alternations during binocular rivalry.

Selected Publications

M.A. Silver, M.P. Stryker. Synaptic density in geniculocortical afferents remains constant after monocular deprivation in the cat. J. Neurosci., 1999.

M.A. Silver, N.K. Logothetis. Grouping and segmentation in binocular rivalry. Vision Res., 2004.

M.A. Silver, D. Ress, D.J. Heeger. Topographic maps of visual spatial attention in human parietal cortex. J. Neurophysiol., 2005.

M.A. Silver, D. Ress, D.J. Heeger. Neural correlates of sustained spatial attention in human early visual cortex. J. Neurophysiol., 2007.

M.A. Silver, N.K. Logothetis. Temporal frequency and contrast tagging bias the type of competition in interocular switch rivalry. Vision Res., 2007.