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Sophie Wuerger, Laura Parkes, Jan-Bernard C Marsman, David C Oxley, Yannis Goulermas; Multivoxel pattern analysis of chromatic responses in LGN and V1. Journal of Vision 2009;9(8):364. doi: 10.1167/9.8.364.
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© ARVO (1962-2015); The Authors (2016-present)
Behavioural measurements have repeatedly shown that the four unique hues are different from the chromatic mechanisms found in the Lateral Geniculate Nucleus (LGN), a sub-cortical structure involved in visual processing: the cone-opponent LGN mechanisms (i.e. cardinal directions ‘L-M’ and ‘S-(L+M)’) do not map onto the colours human observers usually label as red, green, yellow, and blue. Unique hues must therefore be encoded at a later processing stage, in the primary visual cortex or in the extrastriate visual areas. We use multi-voxel pattern analysis (MVPA) to study the spatial clustering of color-selective neurons in the human brain. Our main objective was to investigate whether MVPA reveals the spatial arrangements of color-selective neurons in LGN and in human primary visual cortex (V1). We measured the distributed fMRI activation patterns for different color stimuli (Experiment 1: cardinal colors (to which the LGN is known to be tuned), Experiment 2: unique hues) in LGN and V1. Our main findings were: (i) In LGN, cone-opponent cardinal directions produce unique activation patterns for each of the three cardinal colour directions. (ii) Cone-opponent cardinal color modulations produce highly reproducible patterns of activity in V1, but these were not unique to each color. These results suggests that V1 neurons with tuning characteristics similar to those found in LGN are not spatially clustered. (iii) Unique activation patterns for perceptual (unique) hues in V1 support current evidence for a spatially clustered hue map.
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