Determinants of human performance on concurrent schedules

Matching provides efficient decisions

How humans and animals distribute their behavior across choice options has been of key interest to economics, psychology, ecology, and related fields. Neoclassical and behavioral economics have provided prescriptions for how decision-makers can maximize their reward or utility, but these formalisms are used by decision-makers rarely. Instead, individuals allocate their behavior in proportion to the worth of their options, a phenomenon captured by the generalized matching law. Why biological decision-makers adopt this strategy has been unclear. To provide insight into this issue, this article evaluates the performance of matching across a broad spectrum of decision situations, using simulations. Matching is found to attain a high or near-optimal gain, and the strategy achieves this level of performance following a single evaluation of the decision options. Thus, matching provides highly efficient decisions across a wide range of choice environments. This result offers a quantitative explanation for the broad adoption of matching by biological decision-makers.

Matching provides efficient decisions

How humans and animals distribute their behavior across choice options has been of key interest to economics, psychology, ecology, and related fields. Neoclassical and behavioral economics have provided prescriptions for how decision-makers can maximize their reward or utility, but these formalisms are used by decision-makers rarely. Instead, individuals allocate their behavior in proportion to the worth of their options, a phenomenon captured by the generalized matching law. Why biological decision-makers adopt this strategy has been unclear. To provide insight into this issue, this article evaluates the performance of matching across a broad spectrum of decision situations, using simulations. Matching is found to attain a high or near-optimal gain, and the strategy achieves this level of performance following a single evaluation of the decision options. Thus, matching provides highly efficient decisions across a wide range of choice environments. This result offers a quantitative explanation for the broad adoption of matching by biological decision-makers.

An evaluation of methods for studying the effects of conditioned reinforcement on human choice

Shahan et al. (2006) found that the relative rate of pigeons' pecking on two observing responses (i.e., responses that only produced an S+ or stimulus correlated with primary reinforcement) was well described by the relative rate of S+ delivery. Researchers have not evaluated the effects of S+ delivery rate in a concurrent observing response procedure with human subjects, so the necessary procedural modifications for studying the effects of conditioned reinforcement on human choice remain unclear. The purpose of the current study was to conduct an additive component analysis of modifications to the procedures of Shahan et al. (2006). We evaluated the additive effects of introducing response cost, a changeover response, and ordinal discriminative stimuli on correspondence with the results of Shahan et al. and the quality of fits of the generalized matching equation. When our procedures were most similar to those of Shahan et al., we observed low rates of observing and indifference between the two observing responses. For the group of subjects with whom all three additive components were included, we obtained the highest level of sensitivity to relative rate of S+ delivery, but the slope and R² of our fits of the generalized matching equation were still much lower than those obtained by Shahan et al. Potential reasons for these discrepancies, methods of resolving them, and implications for future research are discussed.

Qualitative variations in delay discounting: A brief review and future directions

The discounting paradigm has been challenged by an increasing number of studies presenting qualitative variations in the individual discount function. Particularly, the subjective value of a loss does not necessarily systematically decrease with delay to the outcome. Qualitative variation refers to variations in shape rather than steepness of the discount function, such as positive discounting, zero discounting, unsystematic discounting, and negative discounting. Data from three previous studies were analysed in terms of qualitative variations observed in delay discounting patterns. Attention was also given to methods used and to the relationship between the results from the various levels of investigation. We found qualitative differences between discounting of monetary gains and losses on an individual level. While discounting of gains mainly took the form of conventional positive discounting, discounting of losses often took the form of zero discounting or unsystematic discounting. Further, there were more qualitative variations in discounting of both gains and losses among adolescents compared to adults. By examining verbal reports and single choices, we identified some of the rules and consequences involved in these delay discounting patterns. The different rules and consequences observed for the gain and loss scenarios, support that discounting of gains and losses may involve different combinations of reinforcing contingencies. These results point towards a possible way to explain the influences of qualitative variations in delay discounting.

To maximize or randomize? An experimental study of probability matching in financial decision making

Probability matching, also known as the “matching law” or Herrnstein’s Law, has long puzzled economists and psychologists because of its apparent inconsistency with basic self-interest. We conduct an experiment with real monetary payoffs in which each participant plays a computer game to guess the outcome of a binary lottery. In addition to finding strong evidence for probability matching, we document different tendencies towards randomization in different payoff environments—as predicted by models of the evolutionary origin of probability matching—after controlling for a wide range of demographic and socioeconomic variables. We also find several individual differences in the tendency to maximize or randomize, correlated with wealth and other socioeconomic factors. In particular, subjects who have taken probability and statistics classes and those who self-reported finding a pattern in the game are found to have randomized more, contrary to the common wisdom that those with better understanding of probabilistic reasoning are more likely to be rational economic maximizers. Our results provide experimental evidence that individuals—even those with experience in probability and investing—engage in randomized behavior and probability matching, underscoring the role of the environment as a driver of behavioral anomalies.

Zebrafish choice behavior is sensitive to reinforcer rate, immediacy, and magnitude ratios

Behavioral flexibility has, in part, been defined by choice behavior changing as a function of changes in reinforcer payoffs. We examined whether the generalized matching law quantitatively described changes in choice behavior in zebrafish when relative reinforcer rates, delays/immediacy, and magnitudes changed between two alternatives across conditions. Choice was sensitive to each of the three reinforcer properties. Sensitivity estimates to changes in relative reinforcer rates were greater when 2 variable-interval schedules were arranged independently between alternatives (Experiment 1a) than when a single schedule pseudorandomly arranged reinforcers between alternatives (Experiment 1b). Sensitivity estimates for changes in relative reinforcer immediacy (Experiment 2) and magnitude (Experiment 3) were similar but lower than estimates for reinforcer rates. These differences in sensitivity estimates are consistent with studies examining other species, suggesting flexibility in zebrafish choice behavior in the face of changes in payoff as described by the generalized matching law.

Stimulus generalization of behavioral history: Interspecies generality and persistence of generalization gradients

Four pigeons were exposed to a tandem variable-interval (VI) fixed-ratio (FR) schedule in the presence of a 50-pixel (about 15 mm) square or an 80-pixel (about 24 mm) square and to a tandem VI differential-reinforcement-of-low-rate (DRL) schedule when a second 80-pixel or 50-pixel square was present. The values of the VI and FR schedules were adjusted to equate reinforcement rates in the two tandem schedules. Following this, a square-size continuum generalization test was administered under a fixed-interval (FI) schedule or extinction. In the first testing session, response frequency was a graded function of the similarity of the test stimuli to the training stimuli for all pigeons. These systematic generalization gradients persisted longer under the FI schedule than under extinction.

Using Delay Fading Procedures to Increase Self-Control

Children and adolescents, relative to adults, disproportionately favor smaller, immediate outcomes over larger, delayed outcomes. From a behavioral perspective, this sensitivity toward immediate rewards constitutes impulsive choice, which characterizes numerous behavioral health problems commonly observed during childhood (particularly among individuals with neurobehavioral disabilities). Accordingly, a variety of behavioral technologies have been developed and are widely implemented in applied settings (e.g., self-monitoring programs, interdependent group contingencies, individualized token reinforcement programs) to reduce impulsive responding and promote self-control. Although there is a plethora of research literature detailing these interventions, several promising delay fading procedures may also have clinical utility in applied treatment contexts. The purpose of the present review is to highlight contemporary behavior-analytic research involving delay fading procedures that may increase self-control among children and adolescents and facilitate additional research in the area of self-control.

Pre-specified Anxiety Predicts Future Decision-Making Performances Under Different Temporally Constrained Conditions

In real-life circumstances, people occasionally require making forced decisions when encountering unpredictable events and situations that yield socially and privately unfavorable consequences. In order to prevent future negative consequences, it is beneficial to successfully predict future decision-making behaviors based on various types of information, including behavioral traits and/or psychological states. For this prospective purpose, the present study used the Iowa Gambling Task, which simulates multiple aspects of real-life decision-making processes, such as choice preference, selection and evaluation of output feedback, and investigated how anxiety profiles predict decision-making performances under conditions with different temporal pressures on task execution. To conduct a temporally causal analysis, we assessed the trait and state anxiety profiles of 33 young participants prior to the task and analyzed their subsequent decision-making performances. We separated two disadvantageous card decks with high rewards and losses into high- and middle-risk decks, and calculated local performance indexes for decision-making immediately after salient penalty events for the high-risk deck in addition to traditional global performance indexes concerning overall trial outcomes such as final winnings and net scores. For global decision-making, higher trait anxiety predicted more risky choices solely in the self-paced condition without temporal pressure. For local decision-making, state anxiety predicted risk-taking performances differently in the self- and forced-paced conditions. In the self-paced condition, higher state anxiety predicted higher risk-avoidance. In the forced-paced condition, higher state anxiety predicted more frequent choices of the middle-risk deck. These findings suggest not only that pre-specified anxiety profiles can effectively predict future decision-making behaviors under different temporal pressures, but also newly indicate that behavioral mechanisms for moderate risk-taking under an emergent condition should be focused on to effectively prevent future unfavorable consequences when actually encountering negative events.

Decision making in healthy participants on the Iowa Gambling Task: new insights from an operant approach

The Iowa Gambling Task (IGT) has contributed greatly to the study of affective decision making. However, researchers have observed high inter-study and inter-individual variability in IGT performance in healthy participants, and many are classified as impaired using standard criteria. Additionally, while decision-making deficits are often attributed to atypical sensitivity to reward and/or punishment, the IGT lacks an integrated sensitivity measure. Adopting an operant perspective, two experiments were conducted to explore these issues. In Experiment 1, 50 healthy participants completed a 200-trial version of the IGT which otherwise closely emulated Bechara et al.'s (1999) original computer task. Group data for Trials 1–100 closely replicated Bechara et al.'s original findings of high net scores and preferences for advantageous decks, suggesting that implementations that depart significantly from Bechara's standard IGT contribute to inter-study variability. During Trials 101–200, mean net scores improved significantly and the percentage of participants meeting the “impaired” criterion was halved. An operant-style stability criterion applied to individual data revealed this was likely related to individual differences in learning rate. Experiment 2 used a novel operant card task—the Auckland Card Task (ACT)—to derive quantitative estimates of sensitivity using the generalized matching law. Relative to individuals who mastered the IGT, persistent poor performers on the IGT exhibited significantly lower sensitivity to magnitudes (but not frequencies) of rewards and punishers on the ACT. Overall, our findings demonstrate the utility of operant-style analysis of IGT data and the potential of applying operant concurrent-schedule procedures to the study of human decision making.

Convicted of Our Relevance: An Introduction to the Special Issue

“I'd warned her that intellectuals didn't count for much in the scheme of things: but academics are like the clergy in their blind conviction that their vocation has relevance to the rest of the world.” (McCauley, 1990).

In the beginning, the founders of behaviour therapy were quite explicit about the link between basic laboratory research and their new therapies (Eysenck, 1960; Wolpe, 1958). Their claim that behaviour therapy was based on “modern learning theory” was not, however, without controversy (e.g., Breger & McGaugh, 1965; London, 1972); but while the logical necessity for appeal to laboratory research on learning might have been questioned (Breger & McGaugh, 1965), the historical contingencies linking Pavlov's dogs, Masserman's cats, and Wolpe's first systematic desensitisation patients can scarcely be questioned (American Psychological Association, 1980; Kazdin, 1978).

It is equally clear that there was a similar close historical link between laboratory studies of operant behaviour, especially by Skinner and his students, and the development of behaviour modification applications such as reinforcement therapy and the token economy (Kazdin, 1978; Krasner 1971; Skinner, 1953). Again, the continuing necessity for behaviour modification to be linked to basic research in operant behaviour has been challenged (Azrin, 1977; cf. Deitz, 1978) but the historic fact of the relationship is well established (Krasner, 1971).

An Analysis of an Autoclitic Analogue in Pigeons

Using a conditional discrimination procedure, pigeons were exposed to a nonverbal analogue of qualifying autoclitics such as definitely and maybe. It has been suggested that these autoclitics are similar to tacts except that they are under the control of private discriminative stimuli. Instead of the conventional assumption of privacy, which precludes direct manipulation of the controlling variable, the autoclitic was here identified as a response that is jointly determined by its function as a modifier for the consequence of the tact and by some variable that modifies stimulus control of the tact. Following this modified conceptualization, a novel conditional discrimination procedure was developed as an analogue for establishing autoclitic-like behavior in pigeons. Under some conditions, autoclitic-like behavior was established. Methodological challenges in developing an autoclitic analogue in nonhumans are discussed, followed by a consideration of the implications of such analogues for the understanding of verbal and, more broadly, human behavior.

An analysis of switching and non-switching slot machine player behaviour

Learning theory predicts that, given the repeated choice to bet between two concurrently available slot machines, gamblers will learn to bet more money on the machine with higher expected return (payback percentage) or higher win probability per spin (volatility). The purpose of this study was to investigate whether this occurs when the two machines vary orthogonally on payback percentage and volatility. The sample comprised 52 first year psychology students (mean age = 20.3 years, 20 females, 32 males) who had played a gaming machine at least once in the previous 12 months. Participants were administered a battery of questionnaires designed to assess level of knowledge on the characteristics and operation of poker machines, frequency of poker machine play in the past 12 months, personality traits of impulsivity and capacity for cognitive reflection, and gambling beliefs. For the experimental task, participants were instructed to play on two PC-simulated electronic gaming machines (EGMs or slot machines) that differed on payback percentage and volatility, with the option of freely switching between EGMs after a practice phase. Results indicated that participants were able to easily discriminate between machines and manifested a preference to play machines offering higher payback or volatility. These findings diverged from previous findings of no preference for play on higher payback/volatility machines, potentially due to of the current study's absence of the option to make multi-line and multi-credit bets. It was concluded that return rate parameters like payback percentage and volatility strongly influenced slot machine preference in the absence of betting options like multi-line bets, though more research is needed to determine the effects of such betting options on player distribution of money between multiple EGMs.

Radical behaviorist interpretation: Generating and evaluating an account of consumer behavior

This article considers an approach to the radical behaviorist interpretation of complex human social behavior. The chosen context is consumer psychology, a field currently dominated by cognitive models of purchase and consumption. The nature of operant interpretation is considered, and several levels of operant analysis of complex economic behavior in affluent marketing-oriented economies are developed. Empirical evidence for the interpretation is considered, and a case is made for the qualified use of the hypothetico-deductive method in the appraisal of operant interpretations of complex behaviors.

Quantitative integration of single-subject studies: Methods and misinterpretations

Derenne and Baron (1999) criticized a quantitative literature review by Kollins, Newland, and Critchfield (1997) and raised several important issues with respect to the integration of single-subject data. In their criticism they argued that the quantitative integration of data across experiments conducted by Kollins et al. is a meta-analysis and, as such, is inappropriate. We reply that Kollins et al. offered behavior analysts a technique for integrating quantitative information in a way that draws from the strengths of behavior analysis. Although the quantitative technique is true to the original spirit of meta-analysis, it bears little resemblance to meta-analyses as currently conducted or defined and offers behavior analysts a potentially useful tool for comparing data from multiple sources. We also argue that other criticisms raised by Derenne and Baron were inaccurate or irrelevant to the original article. Our response highlights two main points: (a) There are meaningful quantitative techniques for examining single-subject data across studies without compromising the integrity of behavior analysis; and (b) the healthiest way to refute or question findings in any viable field of scientific inquiry is through empirical investigation.

The trouble with babies and the value of bathwater: Complexities in the use of verbal reports as data

Recent interest among behavior analysts in protocol analysis techniques prompts a consideration of some general measurement issues and some special issues relevant to protocol analysis. The development of behavior- analytic method and theory specific to verbal report research is a good thing, and Ericsson and Simon's (1984) book, Protocol Analysis, provides a useful model of integrating psychological theory and the craft of research. But protocol analysis techniques do not provide a magic window to the "world within the skin," and individual researchers should adopt these techniques only after confronting thorny issues such as how to determine the operating characteristics of verbal reports about private events, how to identify public performances to which protocol analysis can be applied productively, and how to maintain theoretical integrity in the empirical search for private events. We also caution against letting enthusiasm (and controversy) regarding protocol analysis distract behavior analysts from the benefits of using verbal report methods to study interesting events that are public in principle but difficult to measure in practice.

Making sense of sensitivity in the human operant literature

Human operant behavior is often said to be controlled by different variables or governed by different processes than nonhuman operant behavior. Support for this claim within the operant literature comes from data suggesting that human behavior is often insensitive to schedules of reinforcement to which nonhuman behavior has been sensitive. The data that evoke the use of the terms sensitivity and insensitivity, however, result from both between-species and within-subject comparisons. We argue that because sensitivity is synonymous with experimental control, conclusions about sensitivity are best demonstrated through within-subject comparisons. Further, we argue that even when sensitivity is assessed using within-subject comparisons of performance on different schedules of reinforcement, procedural differences between studies of different species may affect schedule performance in important ways. We extend this argument to age differences as well. We conclude that differences across populations are an occasion for more precise experimental analyses and that it is premature to conclude that human behavior is controlled by different processes than nonhuman behavior.

Effects of differential reinforcement and rules with feedback on preference for choice and verbal reports

We evaluated the effects of differential reinforcement and accurate verbal rules with feedback on the preference for choice and the verbal reports of 6 adults. Participants earned points on a probabilistic schedule by completing the terminal links of a concurrent-chains arrangement in a computer-based game of chance. In free-choice terminal links, participants selected 3 numbers from an 8-number array; in restricted-choice terminal links participants selected the order of 3 numbers preselected by a computer program. A pop-up box then informed the participants if the numbers they selected or ordered matched or did not match numbers generated by the computer but not displayed; matching in a trial resulted in one point earned. In baseline sessions, schedules of reinforcement were equal across free- and restricted-choice arrangements and a running tally of points earned was shown each trial. The effects of differentially reinforcing restricted-choice selections were evaluated using a reversal design. For 4 participants, the effects of providing a running tally of points won by arrangement and verbal rules regarding the schedule of reinforcement were also evaluated using a nonconcurrent multiple-baseline-across-participants design. Results varied across participants but generally demonstrated that (a) preference for choice corresponded more closely to verbal reports of the odds of winning than to reinforcement schedules, (b) rules and feedback were correlated with more accurate verbal reports, and (c) preference for choice corresponded more highly to the relative number of reinforcements obtained across free- and restricted-choice arrangements in a session than to the obtained probability of reinforcement or to verbal reports of the odds of winning.

Some determinants of remote behavioral history effects in humans

Undergraduates were exposed to a series of reinforcement schedules: first, to a fixed-ratio (FR) schedule in the presence of one stimulus and to a differential-reinforcement-of-low-rate (DRL) schedule in the presence of another (multiple FR DRL training), then to a fixed-interval (FI) schedule in the presence of a third stimulus (FI baseline), next to the FI schedule under the stimuli previously correlated with the FR and DRL schedules (multiple FI FI testing), and, finally, to a single session of the multiple FR DRL schedule again (multiple FR DRL testing). Response rates during the multiple FI FI schedule were higher under the former FR stimulus than under the former DRL stimulus. This effect of remote histories was prolonged when either the number of FI-baseline sessions was small or zero, or the time interval between the multiple FR DRL training and the multiple FI FI testing was short. Response rates under these two stimuli converged with continued exposure to the multiple FI FI schedule in most cases, but quickly differentiated when the schedule returned to the multiple FR DRL.

Examining the generality of children's preference for contingent reinforcement via extension to different responses, reinforcers, and schedules

Studies that have assessed whether children prefer contingent reinforcement (CR) or noncontingent reinforcement (NCR) have shown that they prefer CR. Preference for CR has, however, been evaluated only under continuous reinforcement (CRF) schedules. The prevalence of intermittent reinforcement (INT) warrants an evaluation of whether preference for CR persists as the schedule of reinforcement is thinned. In the current study, we evaluated 2 children's preference for contingent versus noncontingent delivery of highly preferred edible items for academic task completion under CRF and INT schedules. Children (a) preferred CR to NCR under the CRF schedule, (b) continued to prefer CR as the schedule of reinforcement became intermittent, and (c) exhibited a shift in preference from CR to NCR as the schedule became increasingly thin. These findings extend the generality of and provide one set of limits to the preference for CR. Applied implications, variables controlling preferences, and future research are discussed.

Limited matching on concurrent-schedule reinforcement of academic behavior

Three adolescent students with special educational needs were given a choice between completing one of two available sets of math problems. Reinforcers (nickels) across these alternatives were arranged systematically in separate experimental phases according to three different concurrent variable-interval schedules (reinforcement ratios of 2:1, 6:1, and 12:1). Time allocated to the two stacks of math problems stood in linear relationship to the reinforcement rate obtained from each stack, although substantial undermatching and bias were observed for all subjects. However, changes in the schedules were not followed by changes in allocation patterns until adjunct procedures (e.g., changeover delays, limited holds, timers, and demonstrations) were introduced. The necessity of adjunct procedures in establishing matching in applied situations is discussed as a limitation to quantitative applications of the matching law in applied behavior analysis.

Instructional versus schedule control of humans' choices in situations of diminishing returns

Four adult humans chose repeatedly between a fixed-time schedule (of points later exchangeable for money) and a progressive-time schedule that began at 0 s and increased by a fixed number of seconds with each point delivered by that schedule. Each point delivered by the fixed-time schedule reset the requirements of the progressive-time schedule to its minimum value. Subjects were provided with instructions that specified a particular sequence of choices. Under the initial conditions, the instructions accurately specified the optimal choice sequence. Thus, control by instructions and optimal control by the programmed contingencies both supported the same performance. To distinguish the effects of instructions from schedule sensitivity, the correspondence between the instructed and optimal choice patterns was gradually altered across conditions by varying the step size of the progressive-time schedule while maintaining the same instructions. Step size was manipulated, typically in 1-s units, first in an ascending and then in a descending sequence of conditions. Instructions quickly established control in all 4 subjects but, by narrowing the range of choice patterns, they reduced subsequent sensitivity to schedule changes. Instructional control was maintained across the ascending sequence of progressive-time values for each subject, but eventually diminished, giving way to more schedule-appropriate patterns. The transition from instruction-appropriate to schedule-appropriate behavior was characterized by an increase in the variability of choice patterns and local increases in point density. On the descending sequence of progressive-time values, behavior appeared to be schedule sensitive, sometimes even optimally sensitive, but it did not always change systematically with the contingencies, suggesting the involvement of other factors.

Recent reinforcement-schedule research and applied behavior analysis

Reinforcement schedules are considered in relation to applied behavior analysis by examining several recent laboratory experiments with humans and other animals. The experiments are drawn from three areas of contemporary schedule research: behavioral history effects on schedule performance, the role of instructions in schedule performance of humans, and dynamic schedules of reinforcement. All of the experiments are discussed in relation to the role of behavioral history in current schedule performance. The paper concludes by extracting from the experiments some more general issues concerning reinforcement schedules in applied research and practice.

Concurrent reinforcement schedules for problem behavior and appropriate behavior: experimental applications of the matching law

This study evaluated how children who exhibited functionally equivalent problem and appropriate behavior allocate responding to experimentally arranged reinforcer rates. Relative reinforcer rates were arranged on concurrent variable-interval schedules and effects on relative response rates were interpreted using the generalized matching equation. Results showed that relative rates of responding approximated relative rates of reinforcement. Finally, interventions for problem behavior were evaluated and differential reinforcement of alternative behavior and extinction procedures were implemented to increase appropriate behavior and decrease problem behavior. Practical considerations for the application of the generalized matching equation specific to severe problem behavior are discussed, including difficulties associated with defining a reinforced response, and obtaining steady state responding in clinical settings.

Response acquisition by humans with delayed reinforcement

The present experiment examined whether a response class was acquired by humans with delayed reinforcement. Eight white circles were presented on a computer touch screen. If the undergraduates touched two of the eight circles in a specified sequence (i.e., touching first the upper-left circle then the bottom-left circle), then the touches initiated an unsignaled resetting delay culminating in point delivery. Participants experienced one of three different delays (0 s, 10 s, or 30 s). Rates of the target two-response sequence were higher with delayed reinforcement than with no reinforcement. Terminal rates of the target sequence decreased and postreinforcement pauses increased as a function of delay duration. Other undergraduates exposed to yoked schedules of response-independent point deliveries failed to acquire the sequence. The results demonstrate that a response class was acquired with delayed reinforcement, extending the generality of this phenomenon found with nonhuman animals to humans.

People's study time allocation and its relation to animal foraging

In this article we suggest a relation between people's metacognitively guided study time allocation strategies and animal foraging. These two domains are similar insofar as people use specific metacognitive cues to assist their study time allocation just as other species use cues, such as scent marking. People decline to study items that they know they already know, just as other species use a win-shift strategy - avoiding already visited and depleted patches - in foraging. People selectively study the easiest as-yet-unlearned items first, before turning to more difficult items just as other species take the 'just right' size and challenge of prey-the so-called Goldilocks principle. People use a stop rule by which they give up on one item and turn to another when the returns diminish just as others species use a stop rule that guides shifting from one patch to another. The value that each item is assigned on the criterion test, if known during study, influences which items people choose to study and how long they study them just as knowledge of the nutritional or energy value of the food influences choices and perseverance in foraging. Finally, study time allocation strategies can differ in their effectiveness depending upon the expertise of the student just as some species forage close to optimally while others do not.

Effects of modeling versus instructions on sensitivity to reinforcement schedules

This study examined the effects of modeling versus instructions on the choices of 3 typically developing children and 3 children with attention deficit hyperactivity disorder (ADHD) whose academic responding showed insensitivity to reinforcement schedules. During baseline, students chose between successively presented pairs of mathematics problems associated with different variable-interval schedules of reinforcement. After responding proved insensitive to the schedules, sessions were preceded by either instructions or modeling, counterbalanced across students in a multiple baseline design across subjects. During the instruction condition, students were told how to distribute responding to earn the most reinforcers. During the modeling condition, students observed the experimenter performing the task while describing her distribution of responding to obtain the most reinforcers. Once responding approximated obtained reinforcement under either condition, the schedules of reinforcement were changed, and neither instruction nor modeling was provided. Both instruction and modeling interventions quickly produced patterns of response allocation that approximated obtained rates of reinforcement, but responding established with modeling was more sensitive to subsequent changes in the reinforcement schedules than responding established with instructions. Results were similar for students with and without ADHD.

Increasing children's fruit and vegetable consumption: a peer-modelling and rewards-based intervention

OBJECTIVE

To evaluate a peer-modelling and rewards-based intervention designed to increase children's fruit and vegetable consumption.

DESIGN

Over a 5-month period, children in an experimental and a control school were presented with fruit and vegetables at lunchtime. Children aged 5-7 y also received fruit at snacktime (mid-morning). The intervention was implemented in the experimental school and levels of fruit and vegetable consumption were measured at baseline, intervention and at 4-month follow-up.

SETTING

Two inner-city London primary schools.

SUBJECTS

In total, 749 children aged 5-11 y.

INTERVENTION

Over 16 days children watched video adventures featuring heroic peers (the Food Dudes) who enjoy eating fruit and vegetables, and received small rewards for eating these foods themselves. After 16 days there were no videos and the rewards became more intermittent.

MAIN OUTCOME MEASURES

Consumption was measured (i) at lunchtime using a five-point observation scale; (ii) at snacktime using a weighed measure; (iii) at home using parental recall.

RESULTS

Compared to the control school, lunchtime consumption in the experimental school was substantially higher at intervention and follow-up than baseline (P<0.001), while snacktime consumption was higher at intervention than baseline (P<0.001). The lunchtime data showed particularly large increases among those who initially ate very little. There were also significant increases in fruit and vegetable consumption at home (P<0.05).

CONCLUSIONS

The intervention was effective in bringing about substantial increases in children's consumption of fruit and vegetables.