A sequence of two stimuli, S1 and S2, separated by a delay, was presented on every trial. Tasks associated with these sequences differed. For tasks 1, 2, 3 and 6, four sequences (AA, AB, BA and BB) were used. A and B represent tones of different frequencies. For task 4, S1 and S2 were tones of three different frequencies, A, B or C. For task 5, S1 was also a tone (of frequency A, B or C), whereas S2 was a noise burst (D), a frequency-modulated tone (E) or a click train (F). (a) Tasks 1 and 2 required a go response for sequence AA and a nogo response for the other sequences. The WM load was higher when S1 was A (thick orange traces) than when it was B (thin blue traces). Tasks 1 and 2 differed with respect to the hand used for the responses. Putative WM-related activity was identified by a within-task comparison. (b) Task 6 required a go response for sequence BB and a nogo response for the other sequences. The partial changes of stimulus-response associations relative to those of task 1 enabled WM-related activity to be revealed also by between-task comparisons. (c) Task 3, a delayed-response task, required a go response when S1 was A and a nogo response when it was B, irrespective of the frequency of S2. Potential differences in activity related to preparation for go and nogo responses could be revealed by comparing activity during the delay of trials requiring go responses (thin orange traces) and nogo responses (thin blue traces). (d) Task 4, a delayed-match-to-sample task, required a go response when S1 and S2 were identical and a nogo response otherwise. (e) Task 5, a sound-discrimination task, required a go response when S2 was the noise burst and a nogo response when S2 was the click train or the frequency-modulated tone, irrespective of the frequency of S1. WM-related activity was revealed by comparing activity during the delay in tasks 4 and 5. Feedback of whether the response was correct or not was provided to the human subjects in tasks 4 and 5 and to the monkeys in tasks 1 and 6. The human subjects were shown a smiling face immediately after a correct response and a frowning face after an incorrect response. For the monkeys, a drop of water was provided immediately after correct go and nogo responses.