Ready…Go: Amplitude of the fMRI Signal Encodes Expectation of Cue Arrival Time
(A) In each trial, a gray ring (ready cue) appeared and remained on the screen. After several seconds (readiness period, 4–12 s, randomly interleaved), the ring became filled with green (go cue). Participants pressed a button as quickly as possible when they saw the green. (B) General linear model analysis (see Methods) identified the SMA (peak voxel coordinates in MNI space: −4, 0, 52) and STG (peak at 60, 9, −9) as regions whose activity was greater with increasing readiness periods (p<0.01, FDR corrected, cluster size >15). (C) Time series of the raw fMRI signal in the SMA and STG, averaged within different readiness periods. The vertical gray bar marks the arrival of the go cue. Each horizontal bar indicates a different readiness period; the left end of each bar represents the onset of the ready signal. The fMRI signal remained near baseline during the readiness period and rose sharply at the onset of the go signal. Longer readiness period caused higher blood flow after the appearance of the go cue. Asterisks represent the time points at which the fMRI signal amplitude correlates significantly with the time between the ready and go cue (p<0.001). Note that there is no significant correlation at the time points before the arrival of the go cue, only after. (D) The amplitude of the fMRI signal after the go cue correlates with the readiness period (p-values of the correlation, inset). Each point represents the average between measurements taken at 4 and 8 s post-go-cue (see inset). Error bars SEM.