Methylphenidate and stimulus control of avoidance behavior

The introduction of a warning signal that preceded a scheduled shock modified the temporal distribution of free-operant avoidance responses. With response-shock and shock-shock intervals held constant, response rates increased only slightly when the response-signal interval was reduced. The result is consistent with Sidman's (1955) findings under different conditions, but at variance with Ulrich, Holz, and Azrin's (1964) findings under similar conditions. Methylphenidate in graded doses increased response rates, modifying frequency distributions of interresponse times. Drug treatment may have disrupted a "temporal discrimination" formed within the signal-shock interval. More simply, methylphenidate influenced response rates by increasing short response latencies after signal onset; this effect was more prominent than the drug's tendency to increase the frequency of pre-signal responses. When signal-onset preceded shock by 2 sec, individual differences in performance were marked; methylphenidate suppressed responding in one rat as a function of increasing dose levels to a greater degree than in a second animal, but both subjects received more shocks than under control conditions.     

Comparison of stimulus control and reinforcement control effects on imitative behavior

An attempt was made to evaluate reinforcement and stimulus control of imitative and non-imitative behavior. The imitative response required the subject to duplicate the experimenter's response by matching blocks that varied in color. The factor designed to evaluate stimulus control was fading, a procedure that systematically varies the differences between the imitative and non-imitative stimuli. The topography and duration of the non-imitative stimuli were faded in. The factors designed to evaluate reinforcement control were differential reinforcement of non-imitative behavior and time out from positive reinforcement. The results showed stimulus control of non-imitation to be more important than reinforcement control, and that reinforcing events were not sufficient to control non-imitation; while the arrangement of stimulus events was sufficient to control non-imitation. These results were related to studies providing evidence for the processes of discrimination and generalization.     

Intertrial interval effects on internal stimulus control of behavior in brightness differential conditioning

In Experiment 1, groups were given a trial sequence in differential conditioning in which all S+ trials preceded all S? trials (+? schedule) or one in which some S+ trials followed S? trials (+?+ schedule) and either a 1- or a 30-min intertrial interval (ITI). ITI affected discrimination learning only in the +? schedule condition; schedule affected discrimination only at massed trials. In Experiment.2, all groups received a +?+ schedule. In two groups, given a 1- or 15-min ITI between all trials, discrimination learning was independent of ITI. Discrimination learning was facilitated in two other groups given a 1-min ITI between all trials except between S? and the subsequent S+ trial, when the ITI was either 15 or 60 min. The results were discussed in terms of their implications for internal reward-related stimulus control of behavior in differential conditioning.     

Stimulus control of avoidance behavior

The introduction of a warning signal preceding shocks greatly increased the effectiveness of avoidance responding. Periods of “warm-up” at the beginning of the session were eliminated, and the number of shocks received by the subjects was greatly reduced. With response-shock interval constant, response rate increased as the interval between the response and the onset of the warning signal was shortened. The response tended to occur shortly after the onset of the warning signal regardless of the duration of these “safe” periods. A greatly elevated response rate was maintained even when the duration of the safe period was reduced to 0.3 sec. Thus, the pre-shock signal obtained nearly exclusive control of the responding and overrode the usual “temporal discrimination” of the response-shock interval.     

Some determinants of inhibitory stimulus control

Interspersed reinforcement and extinction during discrimination learning generate a U-shaped gradient of inhibition about the stimulus correlated with extinction. The present work showed that extinction is not a necessary determinant of inhibitory stimulus control. In Exp. I, a reduction in the rate of reinforcement, through a shift from a multiple variable-interval 1-min variable-interval 1-min schedule to a multiple variable-interval 1-min variable-interval 5-min schedule, resulted in a post-discrimination line orientation gradient of inhibition about the stimulus correlated with the variable-interval 5-min schedule. In Exp. II, the rates of reinforcement, correlated with a pair of stimuli, were held constant during a shift from a multiple variable-interval 1-min variable-interval 1-min schedule to a multiple variable-interval 1-min differential-reinforcement-of-low-rate schedule. Inhibitory stimulus control about the stimulus correlated with the differential reinforcement of low rate was obtained. In both experiments, a reduction in the rate of responding during one stimulus and behavioral contrast during the other stimulus preceded the observation of inhibitory stimulus control.     

The normalizing effects of methylphenidate on the classroom behavior of ADDH children

This study examined whether methylphenidate normalizes the behavior of hyperactive children (ADDH). Twenty-eight ADDH children were treated for 8 weeks with a mean dose of 41.5 mg/d of methylphenidate. Their classroom behavior and that of normal children was recorded by observers who were blind to diagnosis and treatment. Before treatment, all measures significantly differentiated the ADDH and normal children. After treatment, the two groups were indistinguishable on measures of gross and minor motor movement, noncompliance, interference, and overall hyperactivity. ADDH children were significantly improved on measures of attention but continued to be significantly less attentive. In many ways, the ADDH children were not only improved but indistinguishable from their normal peers.This paper was supported by NIMH grants 30822 and 18579. We gratefully acknowledge the assistance of Beth Landa, Ph.D., who performed the statistical analyses.     

Response persistence: the effects of stimulus control on negatively reinforced problem behavior in a concurrent operant

In the context of instructional demands, compliance and problem behavior can be considered concurrent operants. Of applied interest is increasing one response (i.e., compliance) while decreasing the other (i.e., problem behavior). Strategic arrangement of reinforcement can alter response allocation accordingly. Such schedules can also influence response persistence and generalization. A case study is used to illustrate the effects of stimulus-reinforcer relations in a concurrent-operants arrangement involving an adult with developmental disabilities and problem behavior. Results are discussed in the context of basic operant research findings in the areas of stimulus control and behavioral persistence.     

Extinction of avoidance in rats: response availability and stimulus presentation effects

A conditioned a versive stimulus presented in prolonged, continuous fashion is said to be flooded. Using a two-way shuttle avoidance task. Polin (1959) found that animals allowed to respond to flooded stimuli extinguish faster than animals prevented from responding to discrete stimuli of equal total duration. But, as Shearman (1970) noted, the CS presentation and response availability factors were confounded. He arranged them factorially, in a 2 × 2 design, again utilizing two-way avoidance, but found no differences between any of the experimental groups, although all groups extinguished faster than a regular extinction control group, the only group for which CS termination was response-contingent. Since there is evidence from one-way avoidance studies that response prevention facilitates extinction of avoidance with CS exposure held constant (Shipley et al., 1971). we repeated the Shearman design, using a one-way avoidance paradigm, and including a group for whom the aversive CS would be presented in discrete trials at increasing intensities. A separate aspect of the present investigation concerned the measurement of a fear response as well as the avoidance response. Results of several investigations have shown (e.g. Coulter et al. 1969; Linton et al.. 1970) that avoidance behaviour can be extinguished without the extinction of fear. It was thought useful to assess the generality of this result, since in two-factor theory, fear and avoidance are related.Two supplementary experiments replicated important conditions of the initial one, while examining whether response prevention and response non-availability have similar effects (II), and the relation between the fear test and the test for extinction (III).     

Observing behavior and atypically restricted stimulus control

Restricted stimulus control refers to discrimination learning with atypical limitations in the range of controlling stimuli or stimulus features. In the study reported here, 4 normally capable individuals and 10 individuals with intellectual disabilities (ID) performed two-sample delayed matching to sample. Sample-stimulus observing was recorded with an eye-tracking apparatus. High accuracy scores indicated stimulus control by both sample stimuli for the 4 nondisabled participants and 4 participants with ID, and eye tracking data showed reliable observing of all stimuli. Intermediate accuracy scores indicated restricted stimulus control for the remaining 6 participants. Their eye-tracking data showed that errors were related to failures to observe sample stimuli and relatively brief observing durations. Five of these participants were then given interventions designed to improve observing behavior. For 4 participants, the interventions resulted initially in elimination of observing failures, increased observing durations, and increased accuracy. For 2 of these participants, contingencies sufficient to maintain adequate observing were not always sufficient to maintain high accuracy; subsequent procedure modifications restored it, however. For the 5th participant, initial improvements in observing were not accompanied by improved accuracy, an apparent instance of observing without attending; accuracy improved only after an additional intervention that imposed contingencies on observing behavior. Thus, interventions that control observing behavior seem necessary but may not always be sufficient for the remediation of restricted stimulus control.