Association for Behavior Analysis International

The magnitude of delay discounting rate depends on a number of genetic, historical, and contextual factors. Two studies will be presented where the type and amount of experience on a novel intertemporal choice procedure lead to differential changes in the impulsive behavior of Lewis and Fischer 344 rats. While Lewis rats rapidly settled into a consistent discounting rate, more extensive training was necessary for Fischer rats to achieve a similar level. In addition, when a reversal in the order of presentation of the5 tested delay values was implemented, Lewis rats adapted more quickly than Fischer 344 rats. Implications of these results to previous findings regarding strain-dependent and procedure-dependent differences in delay discounting will be discussed. A third study will be presented that illustrates the effects that the type and amount of experience with visual stimuli (images of body wash bottles and human faces) have on human subjects' patterns of choice and relative preference. Subjective value was assessed with a sequential ranking task, and standard binary choice trials. The results support previous findings regarding response times during binary choice tasks and suggest a common stimulus valuation process between sequential ranking and binary choice trials.

Differences in impulsive choice between Lewis and Fischer 344 rats have been taken for granted. Experience, however, may reverse differences between these strains. We assessed this possibility with8 Lewis and 8 Fischer 344 rats responding for food in a novel procedure. Rats chose between a small-sooner (SS) and a large-later (LL) food delivery (one versus four pellets). In2 retractable levers,6 pairs of delays (0-0, 0-5, 0-10, 0-20, 0-40, 0-80 s) were arranged to occur within sessions, each providing10 food deliveries and followed by a 1-min time-out. Sessions ended after 70 food deliveries or after1 hour elapsed. Pressing a lever in the back wall inserted the retractable levers, and food delivery retracted them. Pairs of delays were presented in ascending order. Preference for the LL lever decreased with increasing delay to LL food delivery. For both strains indifference occurred at 10-s delay to LL. After extended training, differences in impulsive choice between Lewis and Fischer 344 were not evident. Early in training total response output in delays of 40 and 80 s decreased in Fischer 344 but not in Lewis rats. The implications of these results to previous findings will be discussed.

Extended experience in an impulsive-choice procedure where delay to large-later (LL) food delivery increases several times within sessions, should affect preference for the LL alternative in a procedure where delay to LL food delivery decreases as the session progresses. This possibility was assessed with Lewis and Fischer 344 rats responding in a novel procedure where6 pairs of delays were arranged to occur within sessions in descending order (0-80, 0-40, 0-20, 0-10, 0-5, 0-0 s). Each pair provided 10 choices according to a concurrent-chain schedule. In the initial link, pressing a back lever inserted2 front levers, each associated with a random-time schedule. In the terminal link, pressing either the SS or LL lever produced1 or4 pellets, respectively. After each food delivery, pressing once the back lever was required to restart the cycle. Sessions ended after 70 food deliveries or after1 hour elapsed. In the Lewis rats, preference adapted more rapidly to within-session changes in delay to LL food delivery than in the Fischer 344 rats. The Fischer 344 rats showed less overall responses at delays 0, 5, and 10 s to LL food delivery and their choice were more impulsive than the Lewis rats.

The subjective value of stimuli (e.g., delayed vs. immediate rewards) is often estimated with concurrent choice procedures. Previous reports suggest that preference for a given stimulus is dynamically "established" through choice in binary trials. This study compares estimation of the subjective value of images on a computer screen as a function of (a) image type and (b) method used to estimate value. College students (N = 120) were randomly assigned to1 of4 groups that differed on the type of images presented (plastic bottles/human faces) and the order of exposure to2 value-assessment procedures (sequential Lickert ranking/binary choice trials). Response time (RT) and relative preference were measured. During the binary choice trials RT decreased monotonically with previous exposure to individual images and with relative value of the images in each trial. Experience with sequential ranking trials did not affect the magnitude or the distribution of RTs for either image type. During the sequential ranking procedure RT showed an inverted U distribution as a function of preference only for subjects that did not previously experience the binary choice procedure. This differential effect of exposure was less evident when the images were human faces.