Fig. 1.

Example of AX-CPT/DPX task design. In a–c, typical AX-CPT task designs with known (a), jittered (b), or unknown (c) cue-probe delays are depicted. A probe stimulus (X or Y) is presented following a paired cue stimulus (A or B) in target and nontarget combinations. In a two-alternative-forced choice manner, participants are instructed to respond to both cue and probe stimuli with left or right trigger buttons on a joystick or computer keyboard. In the target AX sequence, X probes following A cues demand a right trigger press; all other cues and probes are to be responded to with the left trigger; 70% of trials are composed of AX cue-probe target pairs, entailing a left-right cue-probe response sequence, and AY, BX, and BY cue-probe nontarget pairs are much more rare (10% trials of each). Habitual responses are expected for AX sequences, whereas AY cue-probe pairs demand reactive control in responding to Y. B cues are expected to elicit proactive control, as the upcoming probe response can be fully prepared, a The delay between cue and probe stimuli is fully known, remaining at 1,000 ms for 250 consecutive trials, b The delay between cue and probe stimuli is jittered (randomly) at around 3,000 ms (±500 ms), c The delay between cue and probe is randomly chosen each trial to be either 1,000 ms or 3,000 ms. D. DPX cue and probe stimuli corresponding to AX-CPT cues and probes. In DPX, 68.75% of trials are AX, 12.5% AY, 12.5% BX, and 6.25% BY