Figure 3

Experiment 2 stimulus and results. (a) Temporal structure of trials in Experiments 2 and 3, where the target flicker was presented with or without a melanopsin-directed pedestal. Sessions started with an adaptation period of 5 min to the low-melanopic background. Participants then completed 240 trials of a 2IFC task, half of which contained a pedestal of melanopic stimulation. Individual trials consisted of two 500 ms intervals, separated by a 500 ms ISI. On trials containing the pedestal, melanopic stimulation rose during a 250 ms cosine window, and stayed high for the two intervals and ISI. During either the first or second interval, sinusoidal flicker directed at the L, M, and S cones was presented around the melanopic pedestal; on the other interval no such flicker was presented. After both intervals were presented, melanopic stimulation ramped back down to the low-melanopic background during another 250 ms cosine window, after which the participant was asked to indicate which of the two intervals contained the flicker—this response was untimed. On trials without the melanopic pedestal, melanopic stimulation stayed at the low-melanopic background level for the duration of the trial, including the 500 ms preceding the first interval. Intervals were indicated with an auditory cue. Participants could take a variable-length break in between blocks. Trial order was pseudorandom. (b) Experiment 2 results. Same format as Fig. 2b.