Figure 1
Discrete trial structure of the task is identical for rats and human participants.
(a) Rats in Experiment 1R initiated a trial by performing a nose poke and maintaining it for a variable delay (stimulus delay; 100–400 ms, uniform distribution), after which the stimulus was presented. The stimulus indicated the location of reward and remained present until a choice was made, which rats indicated by licking either the right or left spout. The stimulus was terminated at first lick contact. If a reward was programmed for the chosen spout, it was delivered after a variable delay provided that rats maintained licking (reward delay; 100–600 ms, uniform distribution). If rats abandoned licking prior to the delay allocated for that trial, then the trial was counted as an unrewarded trial. If no reward was available for the chosen spout (unrewarded trial), there was no external event to indicate the absence of reward and there were no restrictions as to when rats could initiate the next trial. (b) For humans in Experiment 1H, reward was operationalized as discovering contraband items. Participants initiated a trial by pressing the spacebar, after which a male or female photograph (indicated by the face drawing) appeared on the left or right side of the screen. The photographs remained present until participants pressed the left or right response keys down. Rewards, if available, were delivered after a variable delay (1–5 secs) provided participants kept the response key depressed. Unrewarded trials (either through early termination of a key press response by participants or probabilistically determined), were un-signaled.
