Figure 5.

Estimated trial-related signal T reflects trial timing independent of stimulus timing or contrast. (a, b) Spiking (a) and hemodynamics (b) for trials consisting of fixation sequences in which the animal fixated with 15-s periodicity, but the stimulus (three contrasts, including 0%, blank) was shown at 30-s intervals, that is, only at the first fixation of each pair. Insets, corresponding S_STIM and H_STIM, calculated by subtracting away blank-trial signals consisting of responses to the pair of fixations on to the blank monitor starting with the blank stimulus (indicated by blue curves). Note monophasic stimulus-evoked H_STIM with no evidence of oscillatory rebounds during the blank epoch. The trial structure is indicated by the color bars (gray, fixate; red, stimulus; no bar, relax). (c) T per contrast. Inset, optimal HRF_STIM calculated over 30-s trials. Note that the signal T is close to exactly periodic at the 15-s fixation periodicity, with identical amplitudes for the first and second fixation periods independent of stimulus strength or evoked spikes in the first fixation (correlation of calculated T across stimulus contrasts: 0.98 (median of pairwise correlations between each T and the leave-one-out mean of the other two), n = 74 trials total, roughly 25 per contrast). (d–f) Data are presented as in a–c, with the same stimuli, presented at the same 30-s intervals, but with the monkey fixating every 10 s. The stimulus was shown only on the first fixation of each triplet (n = 83 trials total, roughly 28 per contrast). All error bars indicate s.e.m.