FIGURE 1.

A schematic illustration of the event sequence in a trial. Each item in a rapid serial visual presentation (RSVP) stream was presented for 50 ms with no inter-stimulus interval. Each RSVP stream consisted of a digit stream and a letter stream. The procedure involved eight letter-onset conditions. Seven were self conditions in which a participant voluntarily pressed a key to determine the onset time of the switch from the digit sequence to the letter sequence. The voluntary action in these conditions involved a participant voluntarily initiating this switch by pressing the space bar at any arbitrary time (within 10 s). Pre-determined temporal delays occurred between the voluntary key press and the onset of the first capital letter (0–50, 100–150, 200–250, 300–350, 400–450, 600–650, or 800–850 ms). The other condition was an automatic condition, in which the onset time of the letter sequence was automatically determined. In both conditions, participants reported the first, second, third, and fourth targets (T1, T2, T3, and T4, respectively) at the end of the target stream.