The start-stop procedure: estimation of temporal intervals by human subjects.

In four experiments investigating human timing, subjects produced estimates of sample durations by bracketing their endpoints. On each trial, subjects reproduced a sample duration by pressing a button before the estimated sample duration elapsed (start time) and releasing it after the estimated duration elapsed (stop time). From these responses, middle time (start + stop/2) and spread time (stop - start) were calculated, representing the point of subjective equality and the difference limen, respectively. In all experiments, subjects produced middle times that varied directly with sample duration. In Experiment 2, middle times lengthened when feedback was withheld. Consistent with Weber timing, spread times, as well as the standard deviation of middle times, varied directly with middle time (Experiments 1, 3, and 4). On the basis of an internal clock model of timing (Gibbon & Church, 1990), the data permitted inferences regarding memory processes and response threshold. Correlations between start and stop times and between start and spread times agreed with earlier findings in animals suggesting that the variance of temporal estimates across trials is based in part upon the selection of a single temporal memory sample from a reference memory store and upon one or two threshold samples for initiating and terminating each estimate within a trial.

Teaching deception skills in a game-play context to three adolescents with autism.

Baron-Cohen (1992) found that students with autism are impaired in their ability to deceive. A multiple-baseline across-subjects design was conceptualized to test the hypothesis that such students could be taught to deceive. Two conditions were presented in baseline and treatment phases. In Condition 1, the student guessed in which hand a small object was hidden when the experimenter presented two closed fists. In Condition 2, the student hid the object and presented two closed fists to the experimenter for a guess. Reinforcement was delivered contingently upon independent guessing during Condition 1 in both baseline and treatment phases. Under Condition 2, reinforcement was delivered noncontingently during the baseline phase and contingently upon successive approximations to the target behavior of deception during the treatment phase. All students displayed the acquisition of at least three of the responses included in the deception response during the baseline phase, and two students showed an erratic acquisition of the total skill during the baseline phase. Results indicate that students with autism can learn to deceive, even without formal intensive training.

The effects of schedules of reinforcement on instruction-following in human subjects with verbal and nonverbal stimuli.

The experiment reported here represents a partial replication of an experiment by Newman, Buffington, and Hemmes (in press) and analyzes responding in college students as a function of three different schedules of reinforcement (FR 1, FR 2, FR 3) and either verbal discriminative stimuli (instructions) or nonverbal discriminative stimuli (different colored cards). All consequences (tokens) were based on behavior consistent either with the verbal discriminative stimulus (S(D)) or with the nonverbal S(D). The schedule of reinforcement varied across subjects, and accuracy of the verbal and nonverbal S(D)s varied across phases from. Results showed that the behavior of all continuous reinforcement (FR 1) subjects was sensitive to the accuracy of the verbal S(D)s, but the behavior of subjects in the nonverbal S(D) conditions showed more sensitivity than the behavior of subjects in verbal conditions under intermittent schedules (FR 2 and FR 3). These finding suggest that the behavior of subjects in experiments where instructions are sometimes pitted against actual contingencies of reinforcement is a function not only of the instruction, but also of the type of reinforcement schedule used.

Internal clock and memory processes in animal timing.

Temporal control of behavior was investigated within the framework of an internal clock model. Pigeons were exposed to signaled fixed-interval 30-s trials mixed with extended unreinforced (baseline) trials. On unreinforced break trials, the signal was interrupted for a period of time after trial onset. In Experiment 1, comparisons between the peak time obtained on baseline and on break trials produced peak time shifts that were longer than those expected if the clock had stopped during the break but shorter than if the clock had reset. In Experiment 2, systematic manipulations of duration and location of breaks produced peak time shifts that were nonlinear functions of break duration and that varied linearly with break location. The obtained peak times were more consistent with a continuous memory decay model than with the stop-retain or the reset hypotheses.

Pavlovian conditioning of the tickle response of human subjects: temporal and delay conditioning.

Previous studies of the human response to a tickle have demonstrated that subjects will respond to a gesture that signals the onset of a tickle in the same way as to a tickle. Researchers have described this anticipatory response as an "expectation." In the current study, we investigated, from the Pavlovian framework, the response to a verbal stimulus preceding the tickle stimulus. We exposed subjects to experimental phases which included the Neutral Stimulus Alone, 100% Pairing of the Neutral and Unconditioned Stimuli (tickle strokes to the foot), Random Presentation, Partial (75%) Reinforcement, and Temporal Conditioning. Pavlovian conditioning was observed in all phases, suggesting a parsimonious explanation for the expectation effect described by others.

Behavioral contrast: Pavlovian effects and anticipatory contrast.

Two sources of behavioral contrast have been identified previously: Pavlovian stimulus-reinforcer relations and component sequence effects (anticipatory contrast). This study sought to isolate these sources of control procedurally in a four-ply multiple schedule composed of two fixed two-component sequences. Different cues were associated with the first component of each sequence, and contrast effects were studied in these target components. In Experiment 1, differential cuing of Component 2 between sequences and availability of reinforcement during target components were varied across three groups of pigeons; the stimulus-reinforcer relation between target-component cues and schedule of reinforcement in Component 2 was varied within subjects. Control by the Pavlovian relation was demonstrated under all conditions, and anticipatory contrast was not observed. In Experiment 2, target-component duration was systematically varied in the three groups of Experiment 1. Control by the Pavlovian relation was reliably obtained only when target-component behavior was unreinforced, and diminished with increases in component duration. Anticipatory contrast emerged in the two groups for which target-component reinforcement was available. These and other data indicate that Pavlovian effects in multiple schedules may be obscured when the requisite conditions for anticipatory contrast are present.

Maximization of reinforcement by two autistic students with accurate and inaccurate instructions.

The present study examines maximization of reinforcement by two autistic individuals under conditions of no instructions, accurate instructions, and inaccurate instructions. Accuracy of instructions and magnitude of reinforcement for differential responding in a choice paradigm were systematically varied across phases. Subject one maximized reinforcement across all three conditions in seven experimental phases. Subject two maximized across these same seven phases, but also experienced three additional phases. In two of the additional phases, subject two maximized reinforcement. In a ninth phase, when reinforcement was intermittent rather than continuous, he failed to maximize reinforcement. Implications of the results for the controversies surrounding the concept of rule-governed behavior are discussed.

Relative durations of conditioned stimulus and intertrial interval in conditioned suppression.

The effects of the relative durations of the conditional stimulus and the intertrial interval on bar pressing during a conditioned-suppression procedure were examined as a function of two additional variables--type of operant baseline schedule and rate of shock presentation. In Experiment 1, response suppression was compared across components of a multiple fixed-ratio, random-ratio, fixed-interval, random-interval schedule, at relative conditioned-stimulus/intertrial-interval durations of 1/1, 1/4, and 1/9. In Experiment 2, relative conditioned-stimulus/intertrial-interval duration (1/5, 3/3, or 5/1) was manipulated across groups, while shock frequency (2, 6, or 10 shocks/hr) was manipulated within groups. In both experiments, suppression during the signal was virtually complete at all relative durations. Responding was also suppressed during the intertrial interval, but that suppression varied as a function of experimental manipulations. In Experiment 1, intertrial-interval response rates were higher when relative signal duration was 1/9 than when it was 1/1, although both relative signal duration and shock frequency, which covaried, could have contributed to the difference. In Experiment 2, the patterning of response rates between successive shocks was affected by relative duration, absolute rates during the intertrial interval varied as a function of shock frequency, and differences between suppression during the signal and suppression during the intertrial interval were affected by both relative duration and shock frequency. The data support an analysis based upon relationships between shock-correlated and intertrial-interval stimuli and, as assessed by the relative-delay-to-reinforcement metric, are comparable to results that have been reported from experiments using similar manipulations under the autoshaping paradigm.

Conditional acceleration and external disinhibition of operant lever pressing by prereward, neutral, and reinforcing stimuli.

Rats responding under a differential-reinforcement-of-low-rate schedule increased their rates of lever pressing during a 20-second click/flash stimulus that preceded the delivery of a response-independent food pellet. The increase could not be attributed to suppression of collateral behavior that has been said to mediate temporally-spaced responding. We propose that the prereward stimulus functioned as an external disinhibitor of lever pressing that had been inhibited by the constraints of the operant schedule. Support is derived from the observed disinhibitory effects of a 10-second unpaired click/flash stimulus and of unsignaled, response-independent pellets that were presented while the animals were responding under the same schedule.

Positive interaction (induction) in multiple variable-interval, differential-reinforcement-of-high-rate schedules.

The effect of increases in the rate of responding in one component of a multiple schedule upon the rate of responding in a second component was investigated. Pigeons were exposed to a multiple schedule where both components were initially variable-interval schedules having the same parameter value. After rate of key pecking stabilized, one component was changed to a schedule that differentially reinforced high rates of responding. Rate of reinforcement in this varied component was adjusted to remain equal to rate of reinforcement in the constant (variable-interval) component. Four of five pigeons showed a maintained increase in rate of responding during both the constant and varied components, even though rates of reinforcement did not change.