Evaluation of pharmacological treatment of impulsivity in children with attention deficit hyperactivity disorder

We used an assessment that involved competing reinforcer dimensions in a concurrent-schedules arrangement to examine the effects of stimulant medication on impulsivity (i.e., sensitivity of choices to reinforcer immediacy relative to rate, quality, and effort) with 4 students with attention deficit hyperactivity disorder. The assessments were administered in the context of a double-blind, placebo-controlled, counterbalanced reversal design. Reinforcer immediacy was the most influential dimension for 3 of the students and the second most influential dimension for 1 of the students across placebo and medication conditions; medication did not affect these sensitivities.     

IMPULSIVITY IN STUDENTS WITH SERIOUS EMOTIONAL DISTURBANCE: THE INTERACTIVE EFFECTS OF REINFORCER RATE,DELAY, AND QUALITY

We conducted two studies extending basic matching research on self-control and impulsivity to the investigation of choices of students diagnosed as seriously emotionally disturbed. In Study 1 we examined the interaction between unequal rates of reinforcement and equal versus unequal delays to reinforcer access on performance of concurrently available sets of math problems. The results of a reversal design showed that when delays to reinforcer access were the same for both response alternatives, the time allocated to each was approximately proportional to obtained reinforcement. When the delays to reinforcer access differed between the response alternatives, there was a bias toward the response alternative and schedule with the lower delays, suggesting impulsivity (i.e., immediate reinforcer access overrode the effects of rate of reinforcement). In Study 2 we examined the interactive effects of reinforcer rate, quality, and delay. Conditions involving delayed access to the high-quality reinforcers on the rich schedule (with immediate access to low-quality reinforcers earned on the lean schedule) were alternated with immediate access to low-quality reinforcers on the rich schedule (with delayed access to high-quality reinforcers on the lean schedule) using a reversal design. With 1 student, reinforcer quality overrode the effects of both reinforcer rate and delay to reinforcer access. The other student tended to respond exclusively to the alternative associated with immediate access to reinforcers. The studies demonstrate a methodology based on matching theory for determining influential dimensions of reinforcers governing individuals' choices.     

Behavioral assessment of impulsivity: a comparison of children with and without attention deficit hyperactivity disorder

We conducted a brief computer-based assessment involving choices of concurrently presented arithmetic problems associated with competing reinforcer dimensions to assess impulsivity (choices controlled primarily by reinforcer immediacy) as well as the relative influence of other dimensions (reinforcer rate, quality, and response effort), with 58 children. Results were compared for children with attention deficit hyperactivity disorder (ADHD) who were and were not receiving medication, and with typically developing children without ADHD. Within-subject and between-groups analyses of the ordinal influence of each of the reinforcer dimensions were conducted using both time- and response-allocation measures. In general, the choices of children with ADHD were most influenced by reinforcer immediacy and quality and least by rate and effort, suggesting impulsivity. The choices of children in the non-ADHD group were most influenced by reinforcer quality, and the influence of immediacy relative to the other dimensions was not statistically significant. Results are discussed with respect to the implications for assessment and treatment of ADHD.     

A brief computer-based assessment of reinforcer dimensions affecting choice

In an extension of Neef, Shade, and Miller (1994), we used a brief computer-based assessment of differential responsiveness to reinforcer rate, quality, delay, and response effort in affecting the choices of 11 participants. The assessment involved successive presentations of two concurrent sets of math problems, each set associated with competing reinforcer or response dimensions in a counterbalanced fashion. The results showed that the reinforcer and response dimensions differentially affected choice, with time-allocation patterns varying across students.     

ASSESSING INFLUENTIAL DIMENSIONS OF REINFORCERS ON CHOICE IN STUDENTS WITH SERIOUS EMOTIONAL DISTURBANCE

We examined how reinforcer rate, quality, delay, and response effort combined to influence the choices of 6 youths with learning and behavior difficulties, and the viability of an assessment methodology derived from matching theory for determining differential responsiveness to those reinforcer and response dimensions. The students were given two concurrent sets of math problems that were equal on two dimensions but competed on two other dimensions (e.g., one set yielded higher rate and lower quality reinforcement than the other). Competing dimensions were counterbalanced across the six conditions of the initial assessment phase, permitting assessment of each dimension on time allocation. The conditions resulting in the most and least time allocated to one problem set alternative relative to the other were then replicated. Time allocated to each of the problems within sets was differentially affected by the reinforcer and/or response dimensions, with allocation patterns varying across students. The results are discussed in the context of implications for the design of treatments and extrapolations from basic research on matching and behavioral economics.     

A Brief Experimental Analysis of Reinforcer and Response Dimensions Related to Self-Control in an Outpatient Clinic

We conducted an assessment of self-control and impulsivity with 9 children referred to an outpatient clinic for impulsive, inattentive, and hyperactive behaviors. Each condition of the assessment consisted of a choice between 2 concurrently presented math or writing tasks, with 1 alternative reflecting impulsive responding and 1 alternative reflecting self-control. For the participants who demonstrated impulsive responding in 1 of 2 baseline conditions, we systematically varied reinforcer quality, delay to reinforcement, and response effort to evaluate the effects of these dimensions on the participants’ choices. Results of the assessment revealed that 3 participants displayed self-control responding, and 6 participants displayed impulsive responding during baseline conditions. Of the participants who displayed initial impulsivity, all showed self-control when 1 or more response or reinforcement dimensions were modified to bias responding within a brief multielement design. Results provide a unique application of concurrent schedules for conducting a brief assessment of impulsive responding in an outpatient clinical setting.     

A COMPARISON OF THE EFFECTS OF BRIEF RULES, A TIMER, AND PREFERRED TOYS ON SELF-CONTROL

Some children make impulsive choices (i.e., choose a small but immediate reinforcer over a large but delayed reinforcer). Previous research has shown that delay fading, providing an alternative activity during the delay, teaching participants to repeat a rule during the delay, combining delay fading with an alternative activity, and combining delay fading with a countdown timer are effective for increasing self‐control (i.e., choosing the large but delayed reinforcer over the small but immediate reinforcer). The purpose of the current study was to compare the effects of various interventions in the absence of delay fading (i.e., providing brief rules, providing a countdown timer during the delay, or providing preferred toys during the delay) on self‐control. Results suggested that providing brief rules or a countdown timer during the delay was ineffective for enhancing self‐control. However, providing preferred toys during the delay effectively enhanced self‐control.     

TEACHING SELF‐CONTROL WITH QUALITATIVELY DIFFERENT REINFORCERS

This study examined the effectiveness of using qualitatively different reinforcers to teach self‐control to an adolescent boy who had been diagnosed with an intellectual disability. First, he was instructed to engage in an activity without programmed reinforcement. Next, he was instructed to engage in the activity under a two‐choice fixed‐duration schedule of reinforcement. Finally, he was exposed to self‐control training, during which the delay to a more preferred reinforcer was initially short and then increased incrementally relative to the delay to a less preferred reinforcer. Self‐control training effectively increased time on task to earn the delayed reinforcer.     

Self-control in children with autism: response allocation during delays to reinforcement.

This study examined the use of a progressive‐delay schedule of reinforcement to increase self‐control and decrease disruptive behavior in children with autism. When initially given the choice between an immediate smaller reinforcer and a larger delayed reinforcer, all participants chose the smaller reinforcer. When access to the larger reinforcer required either no activity or engaging in a concurrent task during the delay, all participants demonstrated both self‐control and preference for a response requirement. Disruptive behavior decreased during delays that required a concurrent task compared to sessions without an activity requirement.     

Impulsive choice and pre‐exposure to delays: iv. effects of delay‐ and immediacy‐exposure training relative to maturational changes in impulsivity

Impulsive choice describes preference for smaller, sooner rewards over larger, later rewards. Excessive delay discounting (i.e., rapid devaluation of delayed rewards) underlies some impulsive choices, and is observed in many maladaptive behaviors (e.g., substance abuse, gambling). Interventions designed to reduce delay discounting may provide therapeutic gains. One such intervention provides rats with extended training with delayed reinforcers. When compared to a group given extended training with immediate reinforcers, delay‐exposed rats make significantly fewer impulsive choices. To what extent is this difference due to delay‐exposure training shifting preference toward self‐control or immediacy‐exposure training (the putative control group) shifting preference toward impulsivity? The current study compared the effects of delay‐ and immediacy‐exposure training to a no‐training control group and evaluated within‐subject changes in impulsive choice across 51 male Wistar rats. Delay‐exposed rats made significantly fewer impulsive choices than immediacy‐exposed and control rats. Between‐group differences in impulsive choice were not observed in the latter two groups. While delay‐exposed rats showed large, significant pre‐ to posttraining reductions in impulsive choice, immediacy‐exposed and control rats showed small reductions in impulsive choice. These results suggest that extended training with delayed reinforcers reduces impulsive choice, and that extended training with immediate reinforcers does not increase impulsive choice.     

RISKY CHOICE IN PIGEONS AND HUMANS: A CROSS‐SPECIES COMPARISON

Pigeon and human subjects were given repeated choices between variable and adjusting delays to token reinforcement that titrated in relation to a subject's recent choice patterns. Indifference curves were generated under two different procedures: immediate exchange, in which a token earned during each trial was exchanged immediately for access to the terminal reinforcer (food for pigeons, video clips for humans), and delayed exchange, in which tokens accumulated and were exchanged after 11 trials. The former was designed as an analogue of procedures typically used with nonhuman subjects, the latter as an analogue to procedures typically used with human participants. Under both procedure types, different variable‐delay schedules were manipulated systematically across conditions in ways that altered the reinforcer immediacy of the risky option. Under immediate‐exchange conditions, both humans and pigeons consistently preferred the variable delay, and indifference points were generally ordered in relation to relative reinforcer immediacies. Such risk sensitivity was greatly reduced under delayed‐exchange conditions. Choice and trial‐initiation response latencies varied directly with indifference points, suggesting that local analyses may provide useful ancillary measures of reinforcer value. On the whole, the results indicate that modifying procedural features brings choices of pigeons and humans into better accord, and that human—nonhuman differences on risky choice procedures reported in the literature may be at least partly a product of procedural differences.     

Effects of reinforcer rate and reinforcer quality on time allocation: Extensions of matching theory to educational settings

We examined how 3 special education students allocated their responding across two concurrently available tasks associated with unequal rates and equal versus unequal qualities of reinforcement. The students completed math problems from two alternative sets on concurrent variable-interval (VI) 30-s VI 120-s schedules of reinforcement. During the equal-quality reinforcer condition, high-quality (nickels) and low-quality items ("program money" in the school's token economy) were alternated across sessions as the reinforcer for both sets of problems. During the unequal-quality reinforcer condition, the low-quality reinforcer was used for the set of problems on the VI 30-s schedule, and the high-quality reinforcer was used for the set of problems on the VI 120-s schedule. Equal- and unequal-quality reinforcer conditions were alternated using a reversal design. Results showed that sensitivity to the features of the VI reinforcement schedules developed only after the reinforcement intervals were signaled through countdown timers. Thereafter, when reinforcer quality was equal, the time allocated to concurrent response alternatives was approximately proportional to obtained reinforcement, as predicted by the matching law. However the matching relation was disrupted when, as occurs in most natural choice situations, the quality of the reinforcers differed across the response options.     

DELAY‐AMOUNT TRADEOFFS IN CHOICES BY PIGEONS AND RATS: HYPERBOLIC VERSUS EXPONENTIAL DISCOUNTING

An adjusting‐delay procedure was used to study the choices of pigeons and rats when both delay and amount of reinforcement were varied. In different conditions, the choice alternatives included one versus two reinforcers, one versus three reinforcers, and three versus two reinforcers. The delay to one alternative (the standard alternative) was kept constant in a condition, and the delay to the other (the adjusting alternative) was increased or decreased many times a session so as to estimate an indifference point—a delay at which the two alternatives were chosen about equally often. Indifference functions were constructed by plotting the adjusting delay as a function of the standard delay for each pair of reinforcer amounts. The experiments were designed to test the prediction of a hyperbolic decay equation that the slopes of the indifference functions should increase as the ratio of the two reinforcer amounts increased. Consistent with the hyperbolic equation, the slopes of the indifference functions depended on the ratios of the two reinforcer amounts for both pigeons and rats. These results were not compatible with an exponential decay equation, which predicts slopes of 1 regardless of the reinforcer amounts. Combined with other data, these findings provide further evidence that delay discounting is well described by a hyperbolic equation for both species, but not by an exponential equation. Quantitative differences in the y‐intercepts of the indifference functions from the two species suggested that the rate at which reinforcer strength decreases with increasing delay may be four or five times slower for rats than for pigeons.     

Influences of delay and rate of reinforcement on discrete-trial choice

An adjusting procedure was used to measure pigeons' preferences among alternatives that differed in the duration of a delay before reinforcement and of an intertrial interval (ITI) after reinforcement. In most conditions, a peck at a red key led to a fixed delay, followed by reinforcement, a fixed ITI, and then the beginning of the next trial. A peck at a green key led to an adjustable delay, reinforcement, and then the next trial began without an ITI. The purpose of the adjusting delay was to estimate an indifference point, or a delay that made a subject approximately indifferent between the two alternatives. As the ITI for the red key increased from 0 s to 60 s, the green-key delay at the indifference point increased systematically but only slightly. The fact that there was some increase showed that pigeons' choices were controlled by more than simply the delay to the next reinforcer. One interpretation of these results is that besides delay of reinforcement, rate of reinforcement also influenced choice. However, an analysis that ignored reinforcement rate, but considered the delays between a choice response and the reinforcers on subsequent trials, was able to account for most of the obtained increases in green-key delays. It was concluded that in this type of discrete-trial situation, rate of reinforcement exerts little control over choice behavior, and perhaps none at all.     

Choice between single and multiple delayed reinforcers.

Pigeons chose between alternatives that differed in the number of reinforcers and in the delay to each reinforcer. A peck on a red key produced the same consequences on every trial within a condition, but between conditions the number of reinforcers varied from one to three and the reinforcer delays varied between 5 s and 30 s. A peck on a green key produced a delay of adjustable duration and then a single reinforcer. The green-key delay was increased or decreased many times per session, depending on a subject's previous choices, which permitted estimation of an indifference point, or a delay at which a subject chose each alternative about equally often. The indifference points decreased systematically with more red-key reinforcers and with shorter red-key delays. The results did not support the suggestion of Moore (1979) that multiple delayed reinforcers have no effect on preference unless they are closely grouped. The results were well described in quantitative detail by a simple model stating that each of a series of reinforcers increases preference, but that a reinforcer's effect is inversely related to its delay. The success of this model, which considers only delay of reinforcement, suggested that the overall rate of reinforcement for each alternative had no effect on choice between those alternatives.     

Choice with initial and terminal link reinforcement: an alternative self-control paradigm

Self-control is demonstrated when a less desirable immediate outcome is chosen to ensure a substantially better future. In a novel animal analogue of this situation, primary reinforcement was delivered in both the initial and terminal links of a concurrent chain schedule. Rats made initial link choices between equal amounts of ethanol-free or ethanol-containing milk. Choosing the ethanol-free reinforcer resulted in delivery of the larger terminal link reinforcer and was thus analogous to self-control. Self-control decreased as the delay between initial and terminal links increased. The results have implications for human choice situations where decisions are made between two immediately available reinforcement alternatives each associated with a different delayed outcome.     

Probability and delay of reinforcement as factors in discrete-trial choice.

Pigeons chose between two alternatives that differed in the probability of reinforcement and the delay to reinforcement. A peck on the red key always produced a delay of 5 s and then a possible reinforcer. The probability of reinforcement for responding on this key varied from .05 to 1.0 in different conditions. A response on the green key produced a delay of adjustable duration and then a possible reinforcer, with the probability of reinforcement ranging from .25 to 1.0 in different conditions. The green-key delay was increased or decreased many times per session, depending on a subject's previous choices. The purpose of these adjustments was to estimate an indifference point, or a delay that resulted in a subject's choosing each alternative about equally often. In conditions where the probability of reinforcement was five times higher on the green key, the green-key delay averaged about 12 s at the indifference point. In conditions where the probability of reinforcement was twice as high on the green key, the green-key delay at the indifference point was about 8 s with high probabilities and about 6 s with low probabilities. An analysis based on these results and those from studies on delay of reinforcement suggests that pigeons' choices are relatively insensitive to variations in the probability of reinforcement between .2 and 1.0, but quite sensitive to variations in probability between .2 and 0.     

Self‐control as generalized operant behavior by adults with autism spectrum disorder

The present investigation attempted to teach self‐control to 3 adults who had been diagnosed with autism spectrum disorder. Using a self‐control training procedure that coupled a gradual fading of delay to access a large delayed reinforcer with a concurrent work requirement, each participant was exposed to conditions in which baseline levels of choices for large delayed reinforcers and task engagement increased 10‐fold. Furthermore, generalization effects were partially demonstrated in a novel context.     

Effects of reinforcer delays on choice as a function of income level

Three rats earned their daily food ration by responding during individual trials either on a lever that delivered one food pellet immediately or on a second lever that delivered three pellets after a delay that was continuously adjusted to ensure substantial responding to both alternatives. Choice of the delayed reinforcer increased when the number of trials per session was reduced. This result suggests that models seeking closure on choice effects must include a parameter reflecting how preference changes with sessionwide income. Moreover, models positing that reinforcer probability and immediacy (1/delay) function equivalently in choice are called into question by the finding that probability and immediacy produce opposing effects when income level is changed.     

Assessing factors that influence young children's food preferences and choices

Researchers have identified an unbalanced diet as a key risk factor in the etiology of many chronic diseases (World Health Organization, 2003 ). Although researchers have found that numerous factors influence children's food choices, no assessment exists to identify these factors. In Experiment 1, we established preliminary empirical evidence of children's preferences for healthier and less‐healthy foods, and found that 16 of 21 children preferred less‐healthy foods to healthier foods. In Experiment 2, we established the utility of an analogue, competing parameters assessment designed to approximate children's food choices in the natural environment. We identified either quality or immediacy as the most influential parameters governing four of four childrens' food choices. We found that effort influenced the efficacy of these reinforcer parameters in a predictable manner for one of four children.