Transitional and steady-state choice behavior under an adjusting-delay schedule

Twelve rats made repeated choices on an adjusting-delay schedule between a smaller reinforcer (A) that was delivered immediately after a response and a larger reinforcer (B) that was delivered after a delay which increased or decreased by 20% depending on the subject's choices in successive blocks of trials. In two phases of the experiment (100 sessions and 40 sessions), reinforcer sizes were selected which enabled theoretical parameters expressing the rate of delay discounting and sensitivity to reinforcer size to be estimated from the ratio of the indifference delays obtained in the two phases. Indifference delays, calculated from adjusting delays in the last 10 sessions of each phase, were shorter when the sizes of A and B were 14 and 25 μl of a 0.6 M sucrose solution than when they were 25 and 100 μl of the same solution. The ratio of the indifference delays was significantly smaller than that predicted on the basis of an assumed linear relation between reinforcer size and instantaneous reinforcer value, consistent with a previous proposal that this relation may be hyperbolic in form. Estimates of the rate of delay discounting based on the ratio of the two indifference delays (mean, 0.08 s(-1)) were similar to values obtained previously using different intertemporal choice protocols. Estimates of the size-sensitivity parameter (mean 113 μl) were similar to estimates recently derived from performance on progressive-ratio schedules. In both phases of the experiment, adjusting delays in successive blocks of trials were analyzed using the Fourier transform. The power spectrum obtained from individual rats had a dominant frequency that corresponded to a period of oscillation of the adjusting delay between 30 and 100 trial blocks (mean, 78). Power in the dominant frequency band was highest in the early sessions of the first phase and declined with extended training. It is suggested that this experimental protocol may have utility in neurobehavioral studies of intertemporal choice.     

Modeling the effect of reward amount on probability discounting

The present study with college students examined the effect of amount on the discounting of probabilistic monetary rewards. A hyperboloid function accurately described the discounting of hypothetical rewards ranging in amount from $20 to $10,000,000. The degree of discounting increased continuously with amount of probabilistic reward. This effect of amount was not due to changes in the rate parameter of the discounting function, but rather was due to increases in the exponent. These results stand in contrast to those observed with the discounting of delayed monetary rewards, in which the degree of discounting decreases with reward amount due to amount-dependent decreases in the rate parameter. Taken together, this pattern of results suggests that delay and probability discounting reflect different underlying mechanisms. That is, the fact that the exponent in the delay discounting function is independent of amount is consistent with a psychophysical scaling interpretation, whereas the finding that the exponent of the probability-discounting function is amount-dependent is inconsistent with such an interpretation. Instead, the present results are consistent with the idea that the probability-discounting function is itself the product of a value function and a weighting function. This idea was first suggested by Kahneman and Tversky (1979), although their prospect theory does not predict amount effects like those observed. The effect of amount on probability discounting was parsimoniously incorporated into our hyperboloid discounting function by assuming that the exponent was proportional to the amount raised to a power. The amount-dependent exponent of the probability-discounting function may be viewed as reflecting the effect of amount on the weighting of the probability with which the reward will be received.     

Response acquisition by zebrafish (Danio rerio) with delayed reinforcement

Zebrafish (Danio rerio) is a common vertebrate animal model in biomedical research and is a promising species for studying how genes interact with environmental factors in determining behavior. The present study investigated how reinforcement parameters affect zebrafish behavior by assessing response acquisition with delayed reinforcement, which has been studied with other species (e.g., rats, pigeons, humans, etc.) but not with zebrafish. Twenty‐four experimentally naïve subjects were exposed to a tandem fixed‐ratio 1 differential‐reinforcement‐of‐other‐behavior x‐s schedule of reinforcement, where x varied across subjects. There were six different delay‐to‐reinforcement durations and sets of four fish were assigned to each delay duration. All of the fish assigned to a 0‐, 0.5‐, or 1‐s delay acquired responding. Two fish acquired responding with a 3‐s delay and one fish appeared to have acquired it with a 6‐s delay although the latter result was less clear. None acquired responding with a 12‐s delay. These results suggest that zebrafish behavior is sensitive to delays to reinforcement and the time frame over which reinforcement is effective may be limited approximately to 6 s. This time frame is shorter than that found with other species. Practical and theoretical implications of the present finding are discussed.     

Effects of neutral and enthusiastic praise on the rate of discrimination acquisition

Previous research has shown that praise is an effective reinforcer; however, few researchers have evaluated whether qualitative differences in praise affect responding. The purpose of the current study was to compare the effects of neutral, enthusiastic, and no praise on the rate of matching‐to‐sample acquisition during discrete‐trial training with adults diagnosed with autism and an intellectual disability. In addition, we evaluated preference for neutral, enthusiastic, and no praise. All three participants acquired responses slightly faster during the enthusiastic praise condition. Preference assessment results showed that one participant preferred enthusiastic praise, whereas the two other participants showed indiscriminate selections.     

Resurgence of goal-directed actions and habits

This study investigated how goal-directed and habitual behaviors recover after extinction within the context of the resurgence effect, a form of relapse induced by the removal or worsening of alternative reinforcement. Rats were trained to press a target lever with one reinforcer (O1) for either minimal (4) or extended (16) sessions. An extinction test after the completion of O1 devaluation confirmed that minimal and extended training formed goal-directed and habitual behaviors, respectively. Then, pressing an alternative lever was reinforced with a second reinforcer (O2) while the target response was placed on extinction. When O2 was discontinued, the minimally trained target response resurged with goal-directed status as in the extinction test. However, the extinguished habitual behavior in the extensively trained rats did not recover as a habit but instead with goal-directed status, possibly due to the context specificity of habits or the introduction of a new response–reinforcer contingency. The critical finding that reinforcer devaluation consistently led to less resurgence regardless of the amount of acquisition training provides a clinical implication that coupling differential-reinforcement-of-alternative-behavior (DRA) treatments with the devaluation of the associated reinforcer of problematic behavior could effectively diminish its recurrence.     

Stimulus Equivalence: Effects Of A Default-response Option On Emergence Of Untrained Stimulus Relations

Human subjects were exposed to a concurrent-chains schedule in which reinforcer amounts, delays, or both were varied in the terminal links, and consummatory responses were required to receive points that were later exchangeable for money. Two independent variable-interval 30-s schedules were in effect during the initial links, and delay periods were defined by fixed-time schedules. In Experiment 1, subjects were exposed to three different pairs of reinforcer amounts and delays, and sensitivity to reinforcer amount and delay was determined based on the generalized matching law. The relative responding (choice) of most subjects was more sensitive to reinforcer amount than to reinforcer delay. In Experiment 2, subjects chose between immediate smaller reinforcers and delayed larger reinforcers in five conditions with and without timeout periods that followed a shorter delay, in which reinforcer amounts and delays were combined to make different predictions based on local reinforcement density (i.e., points per delay) or overall reinforcement density (i.e., points per total time). In most conditions, subjects' choices were qualitatively in accord with the predictions from the overall reinforcement density calculated by the ratio of reinforcer amount and total time. Therefore, the overall reinforcement density appears to influence the preference of humans in the present self-control choice situation.     

DOES USE OF TANGIBLE REWARDS WITH INDIVIDUAL CHILDREN AFFECT PEER OBSERVERS?1

The common assumption that employing tangible rewards with individual children will have adverse effects upon peer observers was studied in the preschool setting. Multiple-subject, multiple-baseline procedures were applied to two classes of children, aged 3.5 to 6 yr. In each group, three consecutive children with low base rates of in-seat behavior received a verbal contingency and food rewards for sitting, while peers (with either low or high rates of in-seat behavior) received neither food nor teacher attention for sitting. Peer reactions measured were in-seat behavior, aggression, nonaggressive disruptive behavior, and complaints. The procedures neither decreased the in-seat behavior of peer observers, nor increased their aggressive or disruptive behavior. On the contrary, peers with low base rates of sitting initially displayed an abrupt, but temporary, increase in sitting. Moreover, although no compensatory attention was delivered, all children exhibited improved sitting by the end of the study. Complaints, which consisted mainly of requests for rewards, decreased in frequency with successive program phases, and within each phase. It is suggested that the class improvement in sitting behavior and the absence of negative effects on observers may be partially due to the high frequency of attention the teacher maintained for other desired behavior and the lack of attention to children's complaints.     

Limits to preference and the sensitivity of choice to rate and amount of food

Studies of choice holding food‐amount ratio constant while varying food‐rate ratio within sessions showed that local changes in preference depend on relative amount of food. The present study investigated whether sensitivity of choice to food‐rate ratio and sensitivity to food‐amount ratio are independent of one another when food‐rate ratios are varied across sessions and food‐amount ratios are varied within sessions. Food deliveries for rats’ presses on the left and right levers were scheduled according to three different food‐rate ratios of 1:1, 9:1, and 1:9; each food‐rate ratio lasted for 106 sessions and was arranged independently of seven food‐amount ratios (7:1, 6:2, 5:3, 4:4, 3:5, 2:6, and 1:7 food pellets) occurring within sessions in random sequence. Each amount ratio lasted for 10 food deliveries and was separated from another by a 60‐s blackout. Sensitivity to rate ratio was high (1.0) across food deliveries. Sensitivity to amount ratio was low when food rates were equal across alternatives, but was high when rate ratio and amount ratio opposed one another. When rate ratio and amount ratio went in the same direction, choice ratio reached an elevenfold limit which reduced sensitivity to approximately zero. We conclude that three factors affect sensitivity to amount: (1) the limit to preference, (2) the equal effect on preference of amounts greater than four pellets, and (3) the absence of differential effects of switches in amount in the equal‐rates (1:1) condition. Taken together, these findings indicate that rate and amount only sometimes combine independently as additive variables to determine preference when amount ratios vary frequently within sessions.