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Daniela Petrova, Bruce Henning, Andrew Stockman; The temporal characteristics of the early and late stages of the visual pathways signaling brightness and colour. Journal of Vision 2010;10(15):9. doi: 10.1167/10.15.9.
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© ARVO (1962-2015); The Authors (2016-present)
Monochromatic lights change colour and/or brightness when flickered; lights near 560 nm, for example, appear brighter, whereas lights near 650 nm appear yellower. These effects are usually attributed to nonlinearities, possibly located in different visual pathways signaling brightness and colour.
We used the nonlinearities to dissect the temporal characteristics of the two pathways into early (pre-nonlinearity) and late (post-nonlinearity) stages. We used amplitude-modulated flicker with a high carrier-frequency (fc=5-50 Hz) and a low amplitude-modulation-frequency (fam=0.5-5 Hz). The observers set the modulation threshold for detecting the colour or brightness change at fam as a function of fc (to determine the early temporal characteristics) or as a function of fam (to determine the late characteristics). The early and late characteristics, respectively, could be estimated directly above and below about 5 Hz. The characteristics at other frequencies could be inferred from the differences between these functions and the overall temporal contrast sensitivity measured using visible flicker.
For both colour and brightness changes, the early temporal stages were bandpass, peaking at 10-15 Hz and falling-off in sensitivity at both lower and higher frequencies; their shapes were consistent with the nonlinearities being relatively early in both visual pathways. The late stages, in contrast, were similarly low-pass for both the brightness and the colour changes. Any similarities between the inferred filter shapes, however, may be artefactual. The characteristics of the early stage showed evidence for an adaptation-dependent speeding up of the visual response, whereas those of the late stage do not.
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