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Erin Goddard, Robert Hess, Kathy Mullen; Colour and achromatic contrast adaptation: different adaptation effects at detection threshold and suprathreshold contrasts. Journal of Vision 2019;19(8):9. doi: https://doi.org/10.1167/19.8.9.
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© ARVO (1962-2015); The Authors (2016-present)
Prolonged viewing of chromatic contrast (adaptation) can increase detection thresholds as well as reduce the apparent contrast of subsequent stimuli. The selectivity of such effects across different stimuli of colour directions has been used to infer the tuning of distinct colour channels (e.g. Krauskopf, Williams & Heely, 1982, Vis Res). However, effects can vary across paradigms (e.g. Gunther, 2014, JOSA), and adaptation effects on threshold vs suprathreshold stimuli may be mediated by different mechanisms (e.g. Webster & Mollon, 1994, Vis Res).
Here, we compared the effects of adaptation on detection thresholds and suprathreshold apparent contrast for counter-phasing sinusoidal ring stimuli (TF=2Hz, SF=0.5cpd, radius=7.5 degs). We measured the effect of adapting to achromatic (Ach), L-M isoluminant (RG) and S-cone isolating (BY) contrast on detection thresholds (n=10) and apparent contrast (n=10) of Ach, RG and BY test stimuli. As expected, within-stimulus adaptation was stronger than cross-stimulus adaptation for all stimuli across both paradigms, however, cross-stimulus adaptation effects varied significantly. After chromatic adaptation, achromatic test stimuli showed elevated detection thresholds but no change in apparent contrast. Conversely, after achromatic adaptation, chromatic test stimuli had unchanged detection thresholds but reduced apparent contrast.
These results demonstrate that the effects of adaptation on detection thresholds are not predictive of the effects of adaptation on suprathreshold contrast appearance, suggesting that different mechanisms are being adapted in each case. Additionally, the cross-adaptation effects cannot be explained by simply assuming the mechanisms are more broadly tuned, with the asymmetries across stimuli suggesting more complex interactions.
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