Danilova M V, Mollon J D, 2006, "Comparison at a distance" Perception 35 ECVP Abstract Supplement
Comparison at a distance
M V Danilova, J D Mollon
It is remarkable that observers can discriminate stimulus properties with similar precision whether the targets are juxtaposed or are 10 deg apart. We have shown this for spatial frequency, contrast, orientation, and the two cardinal axes of colour space. All stimuli were presented on an imaginary circle of 5 deg diameter, centred on fixation (Danilova and Mollon, 2003 Perception 32 395 - 414; 2006 Vision Research 46 823 - 846). Precision holds even when the targets fall in opposite hemifields. Such discriminations are unlikely to depend on hard-wired comparator units that draw signals of opposite sign from the two arbitrary regions in which the targets fall. Too many dedicated comparators would be needed. It might be objected, however, that some pre-striate cells have large receptive fields, extending across the midline, and so might serve as the dedicated comparators. To test such suggestions, we have measured colour discrimination when the interior of our imaginary circle was occupied by a 'radial Mondrian pattern', whose sectors varied randomly in chromaticity along the same colour axis as the targets. Subjects still exhibited excellent discrimination of patches lying on opposite sides of the Mondrian. The results favour a representation that can travel freely on a cerebral bus.
[Supported by the Wellcome Trust 072684/Z/03/Z.]
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