William Merigan

Research Interests

My research examines two questions.
    My first research theme is  "What is the visual role of the many different classes of retinal ganglion cells in the primate retina". I have studied the function of the P and M ganglion cells in detail, using physiologically guided ibotenic acid injections to damage small clusters of either P or M cells and then studying the effect of their loss with psychophysical methods. These studies showed that P cells are the basis of primate visual actuity and color vision and that M cells mediate the visibility of fast moving visual stimuli. In addition, both types of cell help mediate luminance vision, object perception, and motion perception. I have recently started a new research project to damage individual retinal ganglion cells in order to refine the measures I have made earlier on P and M cells, by extending them to ON and OFF classes of P and M cells and to the effects of damage to individual retinal ganglion cells. With Prof. Walt makous of the Center for Visual Science and Dr. Luca Brigatti of the Department of Ophthalmology I am also studying the visual consequences of retinal ganglion cell loss in patients with glaucoma.
    My second research theme is "How are the complex perceptual and cognitive abilities of primates mediated by the neural processing that takes place in extrastriate visual cortex".  I am studying areas V1, V2, V4, MT, MST, TEO and TE in macaques and related areas in humans. I use single neuron physiology, perceptual testing, and localized excitotoxic lesions to examine the role of these areas in vision.In recent years, I have examined the role of the above areas in short-term memory, texture segmentation, shape recognition, perceptual grouping, visual search and motion perception in macaques. 

Recent projects

I am just starting a study of photoablation of selected ganglion cells in the macaque retina. Rhodamine dextran will be iontoporetically injected into the LGN guided by physiological recording and then allowed to be transported to retinal ganglion cells. 633 nm light from a laser will then be used to reveal the dendritic sturcture of the labelled cells and to photoablate seleted cells. Behavioral testing will then be used to quantify the effect of damage to individual retinal ganglion cells.

A comparison of the perceptual effects of damage to temporal cortex in humans and macaques was done with Krystel Huxlin. Dr. Huxlin is currently studying morphological and neurochemical alterations in the brain that may underlie cortical reorganization after injury.

Visual search in human subjects was used to examine the role of expectation and prior knowledge with Randall Hayes.

Retinotopic loss of some perceptual abilities without complete visual loss was in patients with cortical disorders in collaboration with Alan Freeman and Randall Hayes.

Neurophysiological responses that indicate involvement in visual short-term memory has recently been discovered in our laboratory in neurons of extrastriate cortical area V4. I am currently studying short-term memory for orientation and direction in these neurons with Bernard Gee.

Selected Publications:

• Merigan, W.H. (1989) Chromatic and achromatic vision of macaques: role of the P pathway. Journal of Neuroscience, 9, 776 783.
• Merigan, W. H. and Maunsell, J. H. R. (1990) Macaque vision after mangocellular lateral geniculate lesions.  Visual Neuroscience, 5, 347-352.
• Merigan, W.H. and Katz, L.M. (1990) Spatial resolution across the macaque retina. Vision Research, 30, 985-992.
• Merigan, W.H. and Byrne, C.E. and Maunsell, J.H.R. (1991) Does primate motion depend on the magnocellular pathway. Journal of Neuroscience, 11, 3422-3429.
• Merigan, W.H. and Maunsell, J.H.R. (1993). How parallel are the primate visual pathways. Annual Review of Neuroscience, 16, 369-402.
• Merigan, W.H., Nealey, T.A. and Maunsell, J.H.R. (1993). Visual effects of lesions of cortical area V2 in macaques. Journal of Neuroscience, 13, 3180-3191.
• Merigan, W.H. (1993) Human V4? Current Biology, 3, 226-229.
• Merigan, W.H. (1996) Basic visual capacities and shape discrimination after lesions of extrastriate area V4 in macaques. Visual Neuroscience, 13, 51-60.
• Pasternak, T. and Merigan, W.H. (1994). Motion perception following lesions of the superior temporal sulcus in the monkey. Cerebral Cortex, 4, 247-259.
• Merigan, W.H. and Pham, H.A. 3D shape perception after V4 lesions in macaques. Visual Neuroscience (in press).
• Merigan, W.H., Meyers, S., and Freeman, A. (1997) Parallel processing streams in human visual cortex. Neuroreport, 8, 3985-3991.
• Huxlin, K., and Merigan, W.H. (1998) Deficits in complex visual perception following unilateral temporal lobectomy. Journal of Cognitive Neuroscience, 10, 395-407.
• Huxlin, K. R.,. Saunders, R.C.,, Marchionini, D., Pham, H.A. and Merigan, W. H., (2000). Perceptual deficits after lesions of inferotemporal cortex in macaques. Cerebral Cortex, 10, 671-683.
• Merigan, W. H. and Saunders, R. C. (submitted) Unilateral deficits in visual perception and learning after unilateral inferotemporal cortex lesions in macaques.
  

Research Support

My work is supported by the Howard Hughes Foundation, the National Eye Institute (NIH) and the McDonnell Pew Foundation.