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Luis Garcia-Suarez, Kathy T. Mullen; Motion and form processing in second order colour vision. Journal of Vision 2010;10(15):10. doi: https://doi.org/10.1167/10.15.10.
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© ARVO (1962-2015); The Authors (2016-present)
It is now accepted that human vision can extract information from the visual scene not just by using a first order system, but also by using a second order system that extracts variations in contrast or texture. In a recent study (Garcia-Suarez & Mullen, 2010), we found no global motion processing for second order chromatic limited lifetime RDK elements. Here we investigate second order from processing in colour vision.
Second order stimuli were contrast modulated isoluminant red-green and achromatic static Gabor envelopes with spatial frequencies varying from 0.125 to 1.5 cycles/degree. The carrier was a static flat-spectrum noise, lowpass filtered (2 cycles/degree cut-off) to avoid luminance artefacts from chromatic aberration. The chromatic and achromatic carriers were matched in visibility. Detection thresholds and orientation identification thresholds were measured simultaneously for two observers using a 2AFC paradigm with the method of constant stimuli.
For both chromatic and achromatic conditions, there is a significant gap between detection and orientation identification thresholds, with this gap being greater for the chromatic condition, suggesting that orientation performance is worse for chromatic than for achromatic second order stimuli once any differences in detection are taken into account.
We found form processing for second order stimuli in colour vision, although it may be worse than the achromatic condition. These results suggest that the ventral pathway has specialized in the form processing of second order chromatic stimuli, whereas the MT area (global motion site) from the dorsal pathway only receives functional input from the achromatic system.
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