The effect of fast flicker adaptation on contrast discrimination

For many decades, aspects of spatiotemporal vision were studied via visual-masking and spatiotemporal-flicker measures. More recent studies used fast flicker adaptation (FFAd) to explore the relation between spatial and temporal vision. FFAd is thought to diminish the magnocellular (M) pathway's sensitivity, but only at low spatial frequencies ≤ 2 cpd, as suggested Kaneko et al. (2015) (and supported by Arnold et al., 2016). We compared FFAd effects of four types of flicker conditions: baseline (no flicker), uniform-field flicker (UFF), and pattern flicker (PF) at flicker contrasts of 10% and 50%. We measured FFAd effects by measuring contrast discrimination thresholds (ΔCs) for test-Gabor pedestals at each of four contrasts: 0, 10, 30, and 50%. The spatial frequencies (SFs) of test Gabors were a low, 0.5 and a high, 5 cpd. As expected, we found 1) that for both test-Gabor SFs, ΔCs increased progressively as the contrast of the Gabors increased from 0 to 50%; and 2) that compared to baseline (no flicker), UFF and both PF contrasts significantly increased ΔCs only with the 0.5 cpd test Gabor; with the 5 cpd test Gabor, all FFAs showed minimal differences from the baseline, except at a 10% test contrast. Interestingly, for the 0.5 cpd Gabor, progressively enhanced FFAd effects (larger ΔCs) were obtained as the PF contrast increased from 0% (UFF), through 30%, to 50%. Related to this, another interesting finding was a strong correlation among the obtained FFAd effects across all test-Gabor contrasts when the 0.5 cpd test Gabor but not the 5 cpd test Gabor was used. Overall, these results indicate that contrast-discrimination thresholds obtained with suprathreshold contrast pedestals may provide a more sensitive measure of FFAd effects than do measures of contrast-detection thresholds used in previous studies.