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Sara J. Hutchinson, Alexander D. Logvinenko; An effect of sinusoidal temporal modulation on high-spatial-frequency tritanopia. Journal of Vision 2002;2(7):148. doi: 10.1167/2.7.148.
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There are a few colour phenomena which are caused by paucity of the S-cones. One is tritanopia of the central foveola i.e. S-cone scotoma, usually not seen but which can be made visible under intermitted light (Magnussen et al, 2001 Vision Research 41 2961–2967). It corroborates that the S-cone scotoma is filled in by some neural process.
Another is high-spatial-frequency tritanopia (HSFT). It is observed, e.g. when an achromatic grating is viewed against a coloured background. If spatial frequency of the grating is high enough it may appear tinged with either yellow-green (on yellow background), or blue (on pink background). It was recently shown that HSFT cannot be accounted for by filling-in within the S-cone pathway (Logvinenko, 2001 Perception 30 223–232). Here we present more evidence supporting this conclusion.
We have studied an effect on HSFT, of temporal modulation (range 0.5 – 10 Hz) of yellow (x = 0.452, y = 0.470, lum = 25.0 cd/m2) and pink (x = 0.309, y = 0.239, lum = 25.0 cd/m2) backgrounds against which an achromatic grating (x = 0.316, y = 0.335, lum = 27.5 cd/m2) is presented. Unlike tritanopia of the central foveola, HSFT is not significantly affected by sinusoidal temporal modulation of the background. Within the range 0.5 — 3 Hz, background modulation simply causes an apparent modulation of the apparent tinge of the hitherto neutral grating — it modulates between neutral and apparent yellow-greenish (on the yellow background) or blue (on the pink background). When temporal frequency of the background modulation exceeds 3 Hz, an apparent flickering of the grating disappears despite that flickering of the coloured background is still clearly visible. The apparent colour of the grating appears fused at the level approximately halfway between the two colour poles (neutral and apparent colour observed against non-flickering background). Thus we conclude that tritanopia of the central foveola and HSFT are based on differing neural mechanisms.
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