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Alexa I Ruppertsberg, Sophie M Wuerger, Marco Bertamini; S-cone input into global motion processing. Journal of Vision 2003;3(9):202. doi: 10.1167/3.9.202.
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© ARVO (1962-2015); The Authors (2016-present)
Last year we reported that chromatic global motion extraction in the observer's isoluminant plane appears to be mediated by a red and a green mechanism and that S-cone input in our task was negligible for the majority of observers. We found this by determining the motion discrimination thresholds (81%) as a function of the chromatic contrast in the isoluminant cone-opponent colour-space (S−(M−L) space; isoluminance adjusted for individual observers). We used random dot kinematograms with 300 coloured gaussian blobs (0.22, 1 /s, 5.1 × 4 , 200cm viewing distance). Observers had to distinguish between an interval with random motion and an interval with 40% of the blobs moving either left or right (2IFC). Experiment 1: To support our results for genuine chromatic input into the motion system we added luminance noise to our stimuli and reran the motion discrimination threshold experiment for various directions in the cone-opponent colour-space and find the same result as without added luminance noise. Experiment 2: We established motion discrimination thresholds for a range of spatial and temporal parameters (stimulus size and velocity: 0.22 + 0.86 , 1 /s + 5 /s) and found that S-cones do contribute to global motion extraction.These experiments were carried out with added luminance noise. S-cone contribution depends not only on the stimulus size (0.86 ), but also on the displacement of the stimulus (1.165 ),. Conclusion: There is a genuine chromatic input to global motion processing. The spatial and temporal parameters for which global motion can be extracted are very similar for luminance and red-green RDK's. Whereas, S-cone input to global motion processing is only effective for relatively large displacements (> 1 ) and large stimulus sizes (ca. 1 ).
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