in delivery of the standard, 2-second reward after the programmed delay interval, during which time the light above the delay lever remained illuminated. An immediate-side lever press resulted in delivery of the adjusting reward without any programmed delay. The immediate (adjusting reward) side was set to 1 second access time (half the standard reward) at the beginning of the session. The access time on the immediate side adjusted depending on the subject’s choice in the last trial according to the following rules: an immediate choice resulted in adjustment down of sipper access time by 0.2 seconds, and a delay choice resulted in adjustment up of sipper access time by 0.2 seconds. The adjustment increment, 0.2 seconds, was 20% of the initial adjusting side amount. As the value of the immediate reinforcer adjusts up and down throughout the session, it should have titrated to a value subjectively equivalent to the 2-second standard reward by the end of the session. Therefore, the adjusted amount of the immediate side gives an estimate of the subjective valuation of the delayed reward by the end of the session. The adjusted amount of the immediate side was limited to 2 seconds so that it never became
