Kathy Mullen

Kathy Mullen

Professor Kathy Mullen took her B.A. (Hons) degree in Physiology & Experimental Psychology at St Anne's College, Oxford University. She went on to complete her PhD in 1983 at the University of Cambridge, Department of Physiology with a thesis on the spatio-temporal characteristics of human colour vision, under the supervision of Prof. H.B Barlow FRS.

There followed appointments as Lady Margaret Research Fellow of New Hall College Cambridge, Fellow of New Hall College, Cambridge, and Royal Society University Research Fellow at the Physiological Laboratory, Cambridge between 1983 and 1990. Now she is a Professor at McGill University in the McGill Vision Research Unit at the Department of Opthalmology, Faculty of Medicine, and associate member of the Department of Neurology and Neurosurgery and the Department of Psychology at McGill University, Canada.

Fall Vision Meeting 2007: Color Processing in the Human LGN and Cortex measured with fMRI

I will report on our results measuring the fMRI BOLD responses of the different cortical areas and the LGN to chromatic and achromatic stimuli. We used an fMRI (4T) experimental protocol that controls for attention and allows us to compare responses to L/M opponent (RG), S-cone (BY) and achromatic contrast within the same scan, using sinewave ring stimuli (0.5cpd). Our results cover three main areas. 1. In the cortex we support previous results that BOLD responses in V1 and VO are biased to color, whereas areas MT and V3a show a dominant achromatic response. 2. We find that the LGN responds best to red-green stimuli at 2 & 8 Hz, whereas blue-yellow responses are much more weakly driven at both temporal rates. This suggests that the color response of P-cells, which are red-green sensitive, dominates the fMRI response in human LGN, at least for the conditions used here. 3. When we compare the responses of the LGN and V1 we observe that a key change from the LGN to V1 is a significant relative boost in the blue-yellow response, occurring at the low temporal rate (2Hz). This robust cortical BY response is evident in all color responsive cortical areas.

 

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