Fig. 2.

Four tasks analyzed in this paper. Red bars indicate time intervals that were analyzed. To better understand neural dynamics in the absence of external events, we only analyzed intervals with over 1,000 ms between changes in sensory stimuli. (A) In the vibrotactile-discrimination task of Romo et al. (38), a mechanical probe vibrates the monkey’s finger at one of seven frequencies. Then, there is either a 3- or 6-s delay interval before the monkey’s finger is vibrated again at a different frequency. The monkey’s task is to report whether the frequency of the second stimulus is higher or lower than that of the first. (B) In the context-dependent trace-conditioning task of Saez et al. (39), monkeys were presented with one of two visual stimuli, A or B. After a 1.5-s delay period, the monkey was either rewarded or not. This is a context-dependent task: in context 1, stimulus A is rewarded and stimulus B is not, whereas, in context 2, the associations are reversed (stimulus A is not rewarded and stimulus B is rewarded). Monkeys learned the current context and displayed anticipatory licking after the appropriate stimuli. (C) In the ready-set-go interval-reproduction task of Jazayeri and Shadlen (41), the monkey tracks the duration between ready and set cues in order to reproduce the same interval with a self-initiated saccade at the appropriate time after the set cue. The interval between ready and set cues was at least 1 s for all analyses. (D) In the duration-discrimination task of Genovesio et al. (42), the monkey compares the duration of two stimuli and then reports which stimulus was on longer. The duration of stimulus 1 was at least 1 s for all analyses.