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Thirty rats received training on a peak-interval procedure, where a baseline with a 20-s time of reinforcement was interspersed among cyclic transitions to other reinforcement time values (10, 20, 30, or 40 s), each of which was either in force for only a single session or for 3 sessions. Peak times were close to the time of reinforcement on the 20-s baseline and tracked the new reinforcement times both closely (but not exactly) and very rapidly. Peak time during transitions was affected by the criterion value in force on the previous session, exhibiting a proactive interference effect. Analysis of individual peak times during a session showed that transitions from lower to higher reinforcement time values were usually characterized by abrupt jumps in peak time, whereas descending transitions were mostly smooth but rapid.

We examined how people use social and verbal cues of di}ering priorities in making social decisions[ In Experiment 0\ formally identical lifeÐdeath choice problems were presented in di}erent hypothetical group contexts and were phrased in either a positive or negative frame[ The risk!seeking choice became more domi! nant as the number of kin in an endangered group increased[ Framing e}ects occurred only in a heterogeneous group context where the lives at risk were a mixture of kin and strangers[ No framing e}ect was found when the same problem was presented in the context of a homogeneous group consisting of either all kin or all strangers[ We viewed the framing e}ects to be a sign of indecisive risk preference due to the di}erential e}ects of a kinship cue and a stranger cue on choice[ In Experiment 1\ we presented the lifeÐdeath problem in two arti_cial group contexts involving either 5 billion human lives or 5 billion extraterrestrial lives[ A framing e}ect was found only in the human context[ Two pre!conditions of framing e}ects appear to be social unfamiliarity of a decision problem and aspiration level of a decision maker[ In Experiment 2\ we analyzed the direction of the framing e}ect by balancing the framing[ The direction of the framing e}ect depended on the baseline level of risk preference determined by a speci_c decision context[

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