Figure 1.

The SART for Experiments 1 and 2. In Experiment 1 at the top, open boxes illustrate video screen frames in the sequence presented to the subject. The target stimuli requiring responses were the randomly selected numerals 0–9 and the no-response target was an “X.” Non-target stimuli, which were never responded to, were either a grating presented on the screen above the fixation point or a brief sound. These occurred on every trial but in random order from trial to trial. In Experiment 2 at the bottom, only the sequence of stimuli is illustrated there. The target stimuli requiring responses were the numerals 0–2 and 4–9 and the no-response stimulus was a “3”; there were no non-target stimuli. The dark boxes illustrate the experience (attention state) probes that interrupted the ongoing SART from time to time, and which were different in the two experiments.