a. Block Design schematic. A hypothetical average BOLD response is shown for three blocks of stimulus presentation, which consist of ten trials of three different tasks presented over a 30s time period, followed by 30s of rest. For each period of stimulus presentation, the summed HRF exhibits an initial dip, peak, then plateaus during the majority of the stimulus presentation period, finally dipping below baseline, and eventually stabilizing back at zero before the next block.2b. Event-related design. Three types of stimuli are presented in an interspersed manner with varying temporal delay. If the events are adequately spaced, HRF modeling can be applied to estimate effects of individual trials or stimulus types. ‘