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Sophie M. Wuerger, Alexa I. Ruppertsberg, Marco Bertamini, Jasna Martinovic; Evidence for two unipolar S-cone pathways for global motion processing. Journal of Vision 2004;4(8):847. doi: 10.1167/4.8.847.
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We have previously reported that human observers can extract global motion from random dot kinematograms (RDKs) for S-cone-isolating modulations only if the individual blobs are large (about 1 deg) and the displacement of each blob is more than about 1 deg [1,2] . We have further investigated the role of the S cones for global motion and tested whether motion is extracted by a single, bipolar S cone pathway or by two unipolar mechanisms. We established the colour contrast thresholds for stimuli defined by S-cone decrements or increments (single-colour condition) where threshold is defined as the contrast at which observers can reliably (81% correct) discriminate random motion (0% coherence) from 40% motion coherence. To test whether a single bipolar or two unipolar mechanisms mediate performance, we generated RDKs where half the blobs were yellow-greenish (i.e. S cone decrements) and half the blobs were violet (i.e. S cone increments) and measured colour contrast thresholds for this mixed-colour condition. From the single-colour thresholds we predicted the thresholds for the mixed-colour condition assuming two different models: a single-mechanism model (a single bipolar S-cone pathway) and a two-mechanisms model (an ON S-cone and an OFF S-cone pathway). We found that, for all 5 observers, the two-mechanisms model predicts the mixed-colour thresholds better than the single-mechanism model. We conclude that two unipolar S -cone pathways mediate motion processing in our task. This is consistent with previous findings by McLellan & Eskew . References: 1. A. Ruppertsberg, S. M. Wuerger, and M. Bertamini, “S-cone input to global motion processing,” JoV 3(9), 202 (2003). 2. A. Ruppertsberg, S. M. Wuerger, and M. Bertamini, “The chromatic selectivity of global motion perception,” Vis. Neurosc. 20, 421-428 (2003). 3. J. S. McLellan and R. T. Eskew, “ON and OFF S-cone pathways have different long-wave cone inputs,” Vis. Res. 40, 2449-2465 (2000).
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