Abstract
Previous studies have shown that the voluntary production of visual stimuli modulates visual attention. However, little is known about the attentional mechanisms underlying this effect. To clarify this issue, the present study examined the time required for the accurate identification of visual stimuli voluntarily produced by participants' key presses. Participants observed a stream of numerals presented at the rate of 20 items/s and identified letters embedded in the stream. Under the voluntary condition, the numerical stream switched to the letter stream immediately, 100, 200, 300, 400, 600, or 800 ms after the participants' key presses. Under the automatic condition, the switch from the numerals to the letters occurred automatically so that participants were unable to anticipate the onset of the letters. Participants were asked to report the first four sequential letters. The results showed that the second letter was more frequently reported than were the first, third, or fourth letters under both the voluntary and the automatic conditions. These results suggest that the transient attentional response is triggered by the appearance of a critical item after a delay of a few tens of milliseconds. Importantly, the second letter was reported more frequently when the switch occurred 100, 400, or 600 ms after voluntary production than when the switch occurred automatically. The rates of reporting voluntarily produced letters under the other delay conditions did not differ from those under the automatic condition. Thus, we conclude that voluntary production of target letters causes two phases of transient attentional modulation; the first increases rapidly and decays quickly, and a second similar wave occurs approximately 500 ms after the onset of voluntary production.