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Karen L. Gunther, Karen R. Dobkins; Both L+M and L−M mechanisms contribute to brightness induction. Journal of Vision 2004;4(8):348. doi: https://doi.org/10.1167/4.8.348.
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© ARVO (1962-2015); The Authors (2016-present)
PURPOSE: Perceived brightness is thought to be mediated by a summed input of the luminance (L+M), chromatic red-green (L−M) and chromatic blue-yellow (S−(L+M)) channels. (We will address only the L+M and L−M channels as our stimuli maintain constant S-cone excitation.) A red disk is said to appear “brighter” when surrounded by a black annulus than when surrounded by a white one, referred to as “brightness induction”. Here we asked whether induction occurs only in the luminance (L+M) input to brightness, only in the chromatic (L−M) input, or both. METHODS: In Experiment 1, subjects were presented with a red/green flickering grating and asked to set either equiluminance (via HFP or MDB), which is thought to isolate the L+M mechanism, or equibrightness (via HBM), which is thought to invoke both the L+M and L−M mechanisms. In two-thirds of the trials the red/green grating was flanked vertically with a black/white inducing grating. In the remaining trials, no inducing gratings were present. HFP was performed at 4 and 15 Hz, MDB and HBM at 0 and 4 Hz; all gratings were 0.5 c/deg. Experiment 2 was identical to Experiment 1 except that a simpler stimulus was used: a red/green flickering dot with a black/white flickering annulus, and only the HFP and HBM settings were performed. RESULTS: Both equiluminance and equibrightness settings were found to be significantly affected by the presence of an inducing stimulus. Equibrightness settings, however, were affected to a greater extent, presumably reflecting the added contribution of the L−M mechanism. CONCLUSIONS: Both L+M and L−M mechanisms contribute to brightness induction.
Department of Neuroscience, Oberlin College (KLG) and EY12153 (KRD)
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