Debriefing
Note that when the letters and tones have a short stimulus onset asynchrony (e.g. 200 ms or 395 ms), response times are slower. There is also a big difference in response times depending on whether one or three letters is being encoded. These results suggest that, at these points in time, the participant is still encoding the letters and must wait until the letters have been encoded to respond to the tone. This is strong evidence that encoding the letters and responding to the tone both require attention. Note that at long SOAs (e.g. 1350 ms), there is no difference in response time to the tone in the one or three letter condition. This is because encoding of the letters is complete and the participant can respond to the tone as soon as it is presented. Effectively, in the 1350 ms SOA condition, the participant is no longer in a dual-task situation and therefore does not experience dual-task interference.