Figure 3.

Adapted from Dale and Buckner (31). (Upper) The raw BOLD fMRI signal evoked when either one, two, or three trials of visual checkerboard stimulation are presented. The trials were each 1 sec in duration and separated by 1 sec. The response increases and is prolonged with the addition of multiple trials, indicating it does not saturate going from one to three trials. (Lower) The explicit contribution of each individual trial by subtracting the one-trial condition from the two-trial condition (yielding the estimated response of the second trial) and the two-trial condition from the three-trial condition (yielding the estimated response of the third trial). The three estimated trials are roughly similar, although subtle but clear departures from linearity can be observed. This finding suggests the bold response can be shown to add linearly over trials, although the generalization of this finding to other brain regions and trial types is still an open question.