Humans’ responses to novel stimulus compounds and the effects of training

Twenty-four college students participated in an experiment with stimulus compounds. Subjects learned to discriminate color stimuli that correlated with varying probabilities of reinforcement. Reinforcement consisted of points. For all subjects, two colors signaled a .80 reinforcement probability, and two others signaled a .20 probability. For compound-trained subjects, a fifth compound stimulus (composed of a high-probability color and a low-probability color) was correlated with a .10 reinforcement probability. During testing, interspersed probe trials required subjects to choose between two alternatives: a compound stimulus and either one of its constituent stimuli. Compound-untrained subjects preferred the compound over either individual stimulus, thus showing response summation. However, compound-trained subjects, having had experience with an exemplar compound, showed significantly lower choice proportions for a test compound, indicating that subjects’ responding to novel stimulus compounds is modifiable by experience with a single similar compound.     

Reaction time and probability on isolated terms

The reaction-time probability effect on isolated trials was found to be asymmetrical in an experiment on 64 college students. There was a large drop in RT for a high-probability probe trial embedded in a block of low-probability trials, but a much smaller rise for a low-probability trial embedded in high-probability trials. Thus, low- but not high-probability responses seem to be influenced by characteristics of the trial block. If the basis of the probability effect were the strategic placement of the criterion for response initiation, symmetrical results should have been obtained. A motivational account which accords with the present data is that the subject is ordinarily willing to prepare but is averse to doing so in some (not entirely specified) low-probability circumstances.     

Determinants of reduction in intended effort as a strategy for coping with anticipated failure

The present study investigated the use of reduction in intended effort as a strategy for protecting self-esteem from the threat of anticipated failure. It was hypothesized that people reduce the amount of effort they intend to exert when they expect a low probability of success on a highly ego-relevant task. Female subjects anticipated taking an easy (high probability of success) or difficult (low probability of success) test that was either high or low in ego relevance. Subjects' levels of intended effort and other task-relevant cognitions were assessed. It was found that subjects in the low-probability condition intended to exert less effort on the highly ego-relevant test than did subjects in the high-probability condition; probability of success had no effect on intended effort level on the low ego-relevance test. Subjects also reported that it was a worse day for a test in the low-probability condition than in the high-probability condition. The relevance of these findings to the egotism explanation of learned helplessness effects and general theories of motivation was discussed.     

Commitment, choice and self-control

When offered a choice (Choice Y) between a small immediate reward (2-sec exposure to grain) and a large reward (4-sec exposure to grain) delayed by 4 sec, pigeons invariably preferred the small, immediate reward. However, when offered a choice (Choice X) between a delay of T seconds followed by Choice Y and a delay of T seconds followed by restriction to the large delayed reward only, the pigeon's choice depended on T. When T was small, the pigeons chose the alternative leading to Choice Y (and then chose the small, immediate reward). When T was large, the pigeons chose the alternative leading to the large delayed reward only. The reversal of preference as T increases is predicted by several recent models for choice between various amounts and delays of reward. The preference for the large delayed alternative with long durations of T parallels everyday instances of advance commitment to a given course of action. Such commitment may be seen as a prototype for self-control.     

Effects of High-Probability Request Sequences on Preschoolers' Compliance and Disruptive Behavior

A high-probability request sequence was implemented with three preschool children with developmental delays within their classroom during typical activities. A multiple baseline design across subjects was used to evaluate the effects of the high-probability request sequence on compliant responding to low-probability requests and the occurrence of disruptive behavior. Results of the study indicate that the use of the high-probability request sequence was effective in increasing compliant responding to low-probability requests delivered by two different trainers for all children. No increases in disruptive behavior were noted as a result of using the high-probability request sequence. When the high-probability request sequence was withdrawn, compliant responding to low-probability requests was maintained for all children across time and in different settings.     

Behavioral momentum and stimulus fading in the acquisition and maintenance of child compliance in the home

The provision of a series of requests to which compliance is highly likely (high-probability requests) immediately antecedent to low-probability requests has been used to establish behavioral momentum of compliance. We evaluated a fading procedure for maintaining high levels of compliance obtained with high-probability requests. Fading involved a systematic reduction in the number of high-probability requests and an increase in the latency between the high- and low-probability requests. High levels of compliance for both "do" and "don't" requests were maintained for 16 weeks in a 5-year-old boy with developmental disabilities after the high-probability request sequence was faded. Similar maintenance was obtained for "do" requests in a 15-year-old girl with developmental disabilities. For this subject, however, the high-probability request sequence was ineffective with "don't" requests. When "don't" requests were phrased as "do" requests, the high-probability request sequence produced high levels of compliance to the low-probability request. High levels of compliance to these "do" requests were maintained for 16 weeks after the high-probability request sequence was faded.     

Further evaluation of response-independent delivery of preferred stimuli and child compliance

The effect of a fixed-time (FT) schedule involving the delivery of preferred stimuli prior to the issuance of a low-probability instruction was evaluated with 2 young children with autism. The FT schedule was introduced according to a reversal design with 3 target instructions, 1 for the first child and 2 for the second child. Compliance increased for 2 of the 3 cases. A high-probability instruction sequence and guided compliance were implemented for the second instruction targeted for 1 child, with compliance increasing with guided compliance.     

Motivational effects of smoked marijuana: behavioral contingencies and low-probability activities.

Six adult male research volunteers, in two groups of 3 subjects each, lived in a residential laboratory for 15 days. All contact with the experimenters was through a networked computer system, and subjects' behavior was monitored continuously and recorded. During the first part of each day, they were allowed to socialize. Two cigarettes containing active marijuana (2.7% delta 9-THC) or placebo were smoked during the private work period and the period of access to social activities. Three-day contingency conditions requiring subjects to engage in a low-probability work activity (instrumental activity) in order to earn time that could be spent engaging in a high-probability work activity (contingent activity) were programmed during periods of placebo and active-marijuana smoking. During placebo administration, the contingency requirement reliably increased the amount of time that subjects spent engaged in the low-probability instrumental activity and decreased the time spent engaged in the high-probability activity. During active-marijuana administration, however, the increases in instrumental activity were consistently larger than observed under placebo conditions. The decreases in contingent activity were similar to those seen under placebo conditions. Smoking active marijuana was thus observed to produce increments in instrumental activity under motivational conditions involving contingencies for "work activities."     

BEHAVIORAL MOMENTUM IN THE TREATMENT OF NONCOMPLIANCE

Behavioral momentum refers to the tendency for behavior to persist following a change in environmental conditions. The greater the rate of reinforcement, the greater the behavioral momentum. The intervention for noncompliance consisted of issuing a sequence of commands with which the subject was very likely to comply (i.e., high-probability commands) immediately prior to issuing a low-probability command. In each of five experiments, the high-probability command sequence resulted in a “momentum” of compliant responding that persisted when a low-probability request was issued. Results showed the antecedent high-probability command sequence increased compliance and decreased compliance latency and task duration. “Momentum-like” effects were shown to be distinct from experimenter attention and to depend on the contiguity between the high-probability command sequence and the low-probability command.     

Evidence for a magnitude effect in temporal discounting with pigeons

A magnitude effect in human intertemporal choice is well established-larger rewards or outcomes are discounted over time at a lower rate than are smaller rewards. However, many recent studies have failed to find a corresponding effect in nonhuman animals. Here we report a magnitude effect in temporal discounting for pigeons' choices involving a tradeoff between reward delay and amount. Pigeons chose between a small reward (1-s access to food) after a 2-s delay, and a large reward (4.5-s access to food) after a 28-s delay. Across conditions, the delays to the small and large rewards were increased or decreased, respectively. Temporal discounting functions obtained through a value-estimation procedure showed clear evidence of a magnitude effect: The value of the large reward decreased more slowly with increasing delay than the value of the small reward. We linked this result to a nonlinear relationship between choice and the delays associated with the small and large rewards. The nonlinearity was contrary to the generalized matching law but was predicted by the contextual choice model. Our results confirm the existence of a magnitude effect in nonhuman temporal discounting, showing that this adaptation is not unique to humans.     

The trajectory of the target probability effect

The effect of target probability on detection times is well-established: Even when detection accuracy is high, lower probability targets are detected more slowly than higher probability ones. Although this target probability effect on detection times has been well-studied, one aspect of it has remained largely unexamined: How the effect develops over the span of an experiment. Here, we investigated this issue with two detection experiments that assessed different target probability ratios. Conventional block segment analysis and linear mixed-effects modeling converged on two key findings. First, we found that the magnitude of the target probability effect increases as one progresses through a block of trials. Second, we found, by examining the trajectories of the low- and high-probability targets, that this increase in effect magnitude was driven by the low-probability targets. Specifically, we found that low-probability targets were detected more slowly as a block of trials progressed. Performance to high-probability targets, on the other hand, was largely invariant across the block. The latter finding is of particular interest because it cannot be reconciled with accounts that propose that the target probability effect is driven by the high-probability targets.     

An experimental analysis of impulsivity and impulse control in humans

In choosing between small, immediate and large, delayed reward, an organism behaves impulsively if it chooses the small reward and shows impulse control if it chooses the large reward. Work with nonhumans suggests that impulsivity and impulse control may be derived from gradients of delayed reinforcement. A model developed by Ainslie and by Rachlin suggests that preference for the rewards should be a function of when the choice is made: small reward with no delay may be preferred to large reward with delay X, but adding delay T to both alternatives should shift preference to the large reward. Three experiments investigated this preference reversal in humans, using termination of 90 dba white noise as the reinforcing event. Experiment 1 showed that under some instructional conditions 90-sec noise off with no delay was preferred over 120-sec noise off after a 60-sec delay, but that preference shifted to the large reward when a 15-sec delay (T) was added to both alternatives. Experiment 2 replicated this preference reversal under two conditions of large, delayed reward, and with three rather than two values of T. Experiment 3 confirmed this effect of T and showed that some humans committed themselves to the large reward when commitment could be made some time before presentation of the reward alternatives. These data support the Ainslie-Rachlin model and extend it to human choice behavior.     

EFFECTS OF HIGH-PROBABILITY REQUESTS ON THE SOCIAL INTERACTIONS OF YOUNG CHILDREN WITH SEVERE DISABILITIES

High-probability requests were used to increase social interactions in 3 young boys with severe disabilities who had been identified as severely socially withdrawn. A multiple baseline design across participants was used to evaluate the effects of high-probability request intervention on (a) social initiations, (b) social responses, (c) continued interactions, and (d) performance of high- and low-probability requests. The students were observed in a second setting to examine generalization effects across peers who did not participate in the training sequence and settings. The results demonstrated that the high-probability requests increased the students' responsiveness to low-probability requests to initiate social behavior. Increases were also found in (a) unprompted initiations and extended interactions to the training peers, (b) unprompted initiations and extended interactions to peers who were not involved in the training procedure, and (c) generalized unprompted initiations and interactions in a second nontraining setting. The students maintained increased levels of initiations and interactions after all prompts were removed from both the training and nontraining settings.     

What matters in the cued task-switching paradigm: Tasks or cues?

Schneider and Logan (2006) recently showed that cue-switch and task-switch costs are sensitive to the relative probability of cue switches versus task switches. From this they concluded that taskswitch costs reflect priming of cue-cue transitions rather than actual task-switching operations. However, because this design confounded probability of specific cue transitions with probability of task switches, the results could also reflect task-switch-level adjustments. The present experiment (N = 80) pits the critical prediction of the cue-priming account, namely that costs for high-probability cue-cue transitions are smaller than for low-probability cue-cue transitions, against the main prediction of the switch-probability account, namely that switch probability, irrespective of specific cue-cue transitions, determines switch costs. Whereas the cue-priming prediction was rejected, a specific version of the probability account—that subjects are sensitive to the probability of a task switch, given a cue switch—was fully confirmed. Thus, tasks are in fact the critical representational units that determine task-switch cost.     

An account of human “impulsivity” on self-control tasks

Three experiments examined the effects of economic constraint (time restriction—trials restriction) on adult humans' performance on concurrent chained schedules of reinforcement in which terminal links differed both in reward size and pre-reward delay levels. In the first, terminal links offered a long delay (20, 30, 40, 50 sec) followed by 2 points, or a short delay (10 sec) followed by 1 point. Initial links consisted of the same variable interval schedules for each alternative. Subjects showed a conditional sensitivity to increases in delay. Under a time constraint, there was an increasing preference for the smaller reward as the delay to the larger reward was increased, whereas under a trials constraint subjects were totally insensitive to such changes. In the second experiment, this finding was replicated using long and short periods of video game playing as large and small rewards. In the third experiment terminal link parameters remained constant (2 points after 15 sec, or 1 point immediately), but initial link parameters were manipulated (either VI 1-sec, 8-sec, or 20-sec) so that the higher relative rate of reward shifted from being associated with the small reward to being associated with the large reward. Again subjects chose differently under the two constraints. Subjects under the time constraint exhibited a preference for the small reward at all levels of initial link, but under the trials constraint subjects preferred the large reward. Subjects in the time constraint condition thus exhibited a maladaptive insensitivity to changes in the initial link duration. These findings are interpreted as supporting a miscalculation rather than a discounting interpretation of human performance on “self-control” tasks.     

Spatial probability as an attentional cue in visual search

We investigated the role of spatial probabilities in target location during participants' performance of a visual search task. Experiments 1 and 2 demonstrated that spatial probabilities could serve as a powerful attentional bias that produced faster detection of targets in high-probability locations than of those in low- or random-probability locations. The effect could not be explained by repetition priming alone. Moreover, responses to targets in low-probability locations were slowed only when a distractor was present in the high-probability location. In Experiments 3-5, we compared the effects of spatial probability with an explicit endogenous cue and a salient exogenous cue. Facilitation due to spatial probability was independent of any benefit afforded by the explicit endogenous cue but interacted with the salient exogenous cue, such that the exogenous cue validity effect was compressed for targets in the high-probability location. Together, these results suggest that the spatial probabilities governing target location constitute a potent bias of visual processing and, as such, can be considered an attentional cue that differs from both typical explicit endogenous and salient exogenous cues.     

Subjective probability and delay.

Human subjects indicated their preference between a hypothetical $1,000 reward available with various probabilities or delays and a certain reward of variable amount available immediately. The function relating the amount of the certain-immediate reward subjectively equivalent to the delayed $1,000 reward had the same general shape (hyperbolic) as the function found by Mazur (1987) to describe pigeons' delay discounting. The function relating the certain-immediate amount of money subjectively equivalent to the probabilistic $1,000 reward was also hyperbolic, provided that the stated probability was transformed to odds against winning. In a second experiment, when human subjects chose between a delayed $1,000 reward and a probabilistic $1,000 reward, delay was proportional to the same odds-against transformation of the probability to which it was subjectively equivalent.     

Escape from freedom: Choosing not to choose in pigeons

Preference for the availability of food-reinforcement alternatives was investigated with Rachlin and Green's (1972) concurrent-chains self-control paradigm. The terminal link of one chain made available a choice between immediate access to food for T seconds and delayed access to food for 4 seconds. The terminal link of the other chain provided only delayed access to food. When T was reduced to .25 seconds, pigeons began to select the delayed-access key in both terminal links. Even so, the pigeons strongly preferred constraint over choice. This effect could not be accounted for by differences in the actual amount of food obtained in the terminal links, by avoidance of the immediate-reinforcement key when not presented as part of a choice, or by avoidance of a multi-key terminal link. Rather, constraint was preferred over freedom. Apparently, the preference for choice is determined by the particular type of choice offered.     

Processing demands of sequential information

Three experiments examined the processing capacity required to use sequential information in a serial reaction time task with partially predictable sequences. The first two experiments varied the response stimulus interval (RSI) between 0 and 500 msec and found the relative advantage of the high-probability stimulus to be independent of the length of the RSI. The third experiment compared utilization of sequential information either with or without a secondary task. The secondary task did not affect the high-probability stimulus but did increase the amount of time required to respond to the low-probability events. The results are discussed in terms of the attentional demands of memory access.