Color processing in the Human LGN and Cortex measured with fMRI

Kathy T. Mullen, Serge Dumoulin & Robert Hess - McGill Vision Research Unit, Canada

In September 2007, Professor Kathy Mullen presented the work of her and her colleagues in an invited talk at the annual Fall Vision Meeting in collaboration with the Optical Society of America. We were lucky enough to sponsor the lecture, which can be viewed with slides and audio below.

Click here to listen to the talk

Click the above image to view the slides, and listen to Kathy Mullen's talk, which was recorded live. The talk is about 20 minutes long. This presentation has been converted into a Flash file and uses streaming technology, so that you can start watching without waiting for the entire file to download. The presentation will open in a new window and run from start to end automatically, or you can use the controls in the top right corner to pause and navigate from slide to slide if you prefer. Don't forget to turn on your speakers!

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Abstract

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.

Ref: Mullen, K.T., Dumoulin, S.O., McMahon, K.L., de Zubicarary, G.I. & Hess, R.F.  Sensitivity of human retinotopic visual cortex to red-green, blue-yellow and achromatic contrast. European Journal of Neuroscience, 25, 491-502, 2007.

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Professor 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.

Research Interests

The overall aim of Kathy's research is to understand how the color content of the visual scene is encoded and analyzed within the human visual system. Initially, the experimental approaches to color vision were concerned with the very first receptoral stages of vision. Modern approaches to the investigation of color vision, however, are frequently based on the use of visual stimuli, termed iisoluminant, that uniquely activate the responses of the color sensitive pathways in the visual system, so separating the brain's response to color from its response to black & white.

Kathy's general approach is to develop and test models and ideas of how the visual system encodes colour information using the behavioral testing of human vision (psychophysics) and fMRI approaches. She has been addressing the following issues in current and ongoing projects:  

The specialization of different areas of the human brain for colour vision using an fMRI approach.

Color and Form perception - the role of colour in shape and contour.

The parallel processing of motion and colour in human vision - separating first and second order contributions

Contrast normalization in color vision.

Peripheral color vision and models of post-receptoral cone connection..

The cognitive developments of color vision in young children.

Find out more about Kathy and her research by clicking here.

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