Figure 1.

Response-signal speed-accuracy trade-off procedure. Sequence of events in a single trial. In both tasks, the 2-cpd target was 30° tilted to the right or left. In the feature task, all of the distracters were vertical 2-cpd patches. In the conjunction task, some distracters shared the orientation of the target and others share its spatial frequency: the 2-cpd distracters were vertical patches; half the 8-cpd distracters were tilted to the left, and half to the right. A small fixation dot was always present at the center of the screen. To implement the SAT procedure, a response tone was presented after the display at varying time lags ranging from 40 to 2000 ms. Feedback was provided after each trial and block. Each of 5 naive observers performed 13,440 experimental trials over 10 sessions.