Reinforcer pathology,probabilistic choice,and medication adherence in patients with multiple sclerosis

The reinforcer pathology model posits that core behavioral economic mechanisms, including delay discounting and behavioral economic demand, underlie adverse health decisions and related clinical disorders. Extensions beyond substance use disorder and obesity, however, are limited. Using a reinforcer pathology framework, this study evaluates medical adherence decisions in patients with multiple sclerosis. Participants completed behavioral economic measures, including delay discounting, probability discounting, and a medication purchase task. A medical decision-making task was also used to evaluate how sensitivity to mild side effect risk and efficacy contributed to the likelihood of taking a hypothetical disease-modifying therapy. Less steep delay discounting and more intense (greater) medication demand were independently associated with greater adherence to the medication decision-making procedure. More generally, the pattern of interrelations between the medication-specific and general behavioral economic metrics was consistent with and contributes to the reinforcer pathology model. Additional research is warranted to expand these models to different populations and health behaviors, including those of a positive health orientation (i.e., medication adherence).     

Delay reduction: current status.

Delay-reduction theory states that the effectiveness of a stimulus as a conditioned reinforcer may be predicted most accurately by the reduction in time to primary reinforcement correlated with its onset. We review support for the theory and then discuss two new types of experiments that assess it. One compares models of choice in situations wherein the less preferred outcome is made more accessible; the other investigates whether frequency of conditioned reinforcement affects choice beyond the effect exerted by frequency of primary reinforcement.     

Momentary maximizing in concurrent schedules with a minimum interchangeover interval

Eight pigeons were trained on concurrent variable-interval variable-interval schedules with a minimum interchangeover time programmed as a consequence of changeovers. In Experiment 1 the reinforcement schedules remained constant while the minimum interchangeover time varied from 0 to 200 s. Relative response rates and relative time deviated from relative reinforcement rates toward indifference with long minimum interchangeover times. In Experiment 2 different reinforcement ratios were scheduled in successive experimental conditions with the minimum interchangeover time constant at 0, 2, 10, or 120 s. The exponent of the generalized matching equation was close to 1.0 when the minimum interchangeover time was 0 s (the typical procedure for concurrent schedules without a changeover delay) and decreased as that duration was increased. The data support the momentary maximizing theory and contradict molar maximizing theories and the melioration theory.     

TEMPORAL CONTROL ON INTERVAL SCHEDULES: WHAT DETERMINES THE POSTREINFORCEMENT PAUSE?

On fixed-interval or response-initiated delay schedules of reinforcement, the average pause following food presentation is proportional to the interfood interval. Moreover, when a number of intervals of different durations occur in a programmed cyclic series, postreinforcement pauses track the changes in interval value. What controls the duration of postreinforcement pauses under these conditions? Staddon, Wynne, and Higa (1991), in their linear waiting model, propose control by the preceding interfood interval. Another possibility is that delay to reinforcement, signaled by a key peck and/or stimulus change, determines the subsequent pause. The experiments reported here examined the role of these two possible time markers by studying the performance of pigeons under a chained cyclic fixed-interval procedure. The data support the linear waiting model, but suggest that more than the immediately preceding interfood interval plays a role in temporal control.     

Schedule-induced defecation by rats during ratio and interval schedules of food reinforcement.

Lever pressing in rats was maintained by continuous and intermittent schedules of food while defecation was monitored. In Experiment 1, reinforcement densities were matched across variable-ratio and variable-interval schedules for three pairs of rats. Defecation occurred in all 3 rats on the variable-ratio schedule and in all 3 rats on the yoked variable-interval schedule. In Experiment 2, fixed-ratio and fixed-interval schedules with similar reinforcement densities maintained lever pressing. Defecation occurred in 3 of 4 rats on the fixed-ratio schedule and in 4 of 4 rats on the fixed-interval schedule. Almost no defecation occurred during continuous reinforcement in either experiment. These results demonstrate that defecation may occur during both ratio and interval schedules and that the inter-reinforcement interval is more important than the behavioral requirements of the schedule in generating schedule-induced defecation.     

Choice between delayed reinforcers and fixed-ratio schedules requiring forceful responding.

This experiment measured pigeons' choices between delayed reinforcers and fixed-ratio schedules in which a force of approximately 0.48 N was needed to operate the response key. In ratio-delay conditions, subjects chose between a fixed-ratio schedule and an adjusting delay. The delay was increased or decreased several times a session in order to estimate an indifference point--a delay duration at which the two alternatives were chosen about equally often. Each ratio-delay condition was followed by a delay-delay condition in which subjects chose between the adjusting delay and a variable-time schedule, with the components of this schedule selected to match the ratio completion times of the preceding ratio-delay condition. The adjusting delays at the indifference point were longer when the alternative was a fixed-ratio schedule than when it was a matched variable-time schedule, which indicated a preference for the matched variable-time schedules over the fixed-ratio schedules. This preference increased in a nonlinear manner with increasing ratio size. This nonlinearity was inconsistent with a theory that states that indifference points for both time and ratio schedules can be predicted by multiplying the choice response-reinforcer intervals of the two types of schedules by different multiplicative constants. Two other theories, which predict nonlinear increases in preference for the matched variable-time schedules, are discussed.     

Delayed and current stimulus control in successive discriminations

In a successive discrimination in which successively alternating red and green hues signaled component variable-interval schedules, sensitivity of the ratio of responses in the two components to variation in the component reinforcer ratio decreased systematically during the course of the component. This decrease in stimulus control or discrimination over the course of the component was shown to be the result of delayed control of responding during the component by the stimulus transition between components. When the red–green stimulus transition was altered by interpolating a white stimulus at the end of each 60-s component, discrimination at the beginning of the component (measured by the power-function exponent for sensitivity to reinforcement) was reduced. Conditions with the white stimulus inserted in other quarters of the component indicated that the current discriminative stimulus exerts control over responding throughout the component, whereas during about the first half of the component, response differentials are influenced by the transition between discriminative stimuli.     

Additional-delay schedules: A continuum of temporal contingencies by varying food delay

Pigeons performed on discrete-trial, temporally defined schedules in which the food delay (D) was adjusted according to the latency of the key peck (X) and two schedule parameters (t and A). The schedule function was D = A(t − X), where D is the experienced delay between a response and a reinforcer. The schedule parameter t is the maximum value below which the present contingencies occur. A is the additional delay to reinforcement for each second the response latency is shorter than the t value. When A = 0 s, the schedule is a continuous reinforcement schedule with immediate reinforcement. When A = 1 s, the schedule is a conjunctive fixed-ratio 1 fixed-time t-s schedule. When A approaches infinity, the schedule becomes a differential reinforcement of long latency schedule. The latencies for subjects with t = 10 s and t = 30 s were observed with the present schedules having seven values for A between 0 s and 11 s. In addition, the latencies for subjects for which t = 30 s were observed at an A value of 31 s to 41 s. As the A value increased, the latencies approached the t value for subjects for which t = 10 s. The latencies for 30-s-t subjects did not approach t, even when the A value was 41 s. The latencies for 10-s-t subjects at 11-s A value were longer than those under yoked conditions having exactly the same delays/interreinforcement intervals. These results demonstrated a continuum of latency related to the schedule continuum (value of A) at a small t value.