Overview of the temporal characteristics of events in four experimental tasks. Pitch-shift stimuli were triggered at delays of 0 ms or 500–1000 ms after mouse click for motor-vocal task with predictable delay (A) and motor-vocal task with unpredictable delay (B), respectively. Vocal-only task with random delay is illustrated in (C), in which a stimulus was triggered by the computer at a delay of 500–1000 ms after the vocal onset. In the motor-only task as shown in (D), subjects clicked the mouse but no stimulus was delivered. The traces in (A)-(D) denote pitch-shifted voice F0 contours (cents) and TTL control pulses indicating the onset and offset of the stimulus.