A search for symmetry in the conditional discriminations of rhesus monkeys, baboons, and children.

Procedures for generating arbitrary matching-to-sample performances may generate only conditional discriminations. Rational grounds for this distinction are proposed, based on the properties that any equivalence relation must possess. Empirical tests are described for determining whether subjects trained on conditional discriminations are also engaged in true matching to sample. A series of studies than leads to the conclusion that proof of true matching to sample by monkeys, pigeons, or baboons is yet to be provided. Whether the absence of such proof reflects experiential factors or species-defined limitations is not presently clear.     

Incentive processes and the peak shift

Intradimensional operant discrimination schedules were employed, which eliminated the covariation of response and reinforcement rates that are found on most operant baselines. In Phase 1, one keylight (S(1)) controlled an increase in pigeons' treadle pressing, relative to another keylight (S(2)), while being correlated with a decrease in frequency of reinforcement. In Phase 2 both treadle pressing and reinforcement increased in the presence of one keylight, relative to the second. In Phase 1 the relatively flat treadle-press generalization gradients peaked at S(1), whereas the peaks of those in Phase 2 were shifted from S(1) in a direction away from S(2). It was postulated that these positive and negative stimulus-reinforcement contingencies influence the likelihood of obtaining peak shift through the operation of a classically conditioned "central motive state." How response-reinforcement and stimulus-reinforcement contingencies might contribute to the development of inhibitory effects of S(2) is discussed. Autoshaped key pecking also was produced by these procedures. During manipulations of stimuli, the gradients obtained for autoshaped key pecking were narrow and sharply peaked at the food-correlated stimulus (S(2)) in Phase 1. This failure to obtain peak shift for an elicited response suggests a difference in discriminative processes operating in classical and instrumental learning.     

Control of adolescents' arbitrary matching-to-sample by positive and negative stimulus relations.

In Experiment 1, four developmentally delayed adolescents were taught an A-B matching-to-sample task with nonidentical stimuli: given Sample A1, select Comparison B1; given A2, select B2. During nonreinforced test trials, appropriate matching occurred when B stimuli appeared as samples and A stimuli as comparisons, i.e., the sample and comparison functions were symmetrical (B-A matching). During A-B or B-A matching test trials in which familiar samples and correct comparisons were presented along with novel comparisons, the subjects selected the correct comparisons. In tests with familiar samples and both incorrect and novel comparisons, subjects selected the novel comparisons, demonstrating control by both positive ("matching") and negative ("nonmatching") stimulus relations in A-B and B-A arrays. In Experiment 2, 12 developmentally delayed subjects were taught a two-stage arbitrary-matching task (e.g., A-B, C-B matching). Test sessions showed sample-comparison symmetry (e.g., B-A, B-C matching) and derived sample-comparison relations (e.g., A-C, C-A matching) for 11 subjects. These subjects also demonstrated control by positive and negative stimulus relations in the derived relations.     

Preference for free choice over forced choice in pigeons

Eight severely retarded young men learned color and line-tilt discrimination. After 95% accuracy was achieved for both dimensions, they were combined to form "conflict-compound" stimuli in which prior reinforcement history was reversed for one element of the compound and unchanged for the other. When responding to the compound was 95% accurate, control exerted by each element was measured. The unchanged element consistently exercised control in agreement with the reinforcement contingencies associated with the compound, regardless of whether it was color or line orientation. The reversed element, which had a conflicting prior history or reinforcement, most often exerted control associated wtih original training, or no control, suggesting that it had been "ignored" during the compound. Conflict compounds produced selective attention. When elements were combined to form "compatible-compound" stimuli, both exercised control in agreement with the compound in post-tests. Selective attention was not produced by compatible compounds.     

ACQUISITION OF EXPRESSIVE SIGNING BY AUTISTIC CHILDREN: AN EVALUATION OF THE RELATIVE EFFECTS OF SIMULTANEOUS COMMUNICATION AND SIGN-ALONE TRAINING

Two methods of training autistic children to use manual signs were compared. Two children, one mute and one capable of some verbal imitation, were taught to use signs as expressive labels for pictures of objects. Using an alternating treatments design, speed of sign acquisition was compared across two training conditions in which signs were presented either accompanied by, or without, the corresponding verbal label. In both conditions, the training procedure incorporated reinforcement, modeling, prompting, fading, and stimulus rotation. The efficacy of training in both treatment conditions was demonstrated by the use of a multiple baseline control across signs, but no clear differences in acquisition speed across conditions were apparent. Posttests conducted to assess stimulus control of signing, and learning of verbal labels when these were present in training, showed that the behavior of the imitative, but not the mute, child was controlled by the verbal stimuli. The implications of the results both for understanding deficits characteristic of autistic children and for developing appropriate language training procedures are discussed.     

Separating the effects of salience and disparity on the rate of observing

Pigeons producing deliveries of grain on a mixed variable-interval, extinction schedule by pecking a center key could also produce discriminative stimuli on concurrent variable-interval schedules by pecking the left or right observing key. The stimuli produced by each observing key were varied independently. In the first experiment, the negative discriminative stimulus was at the far end of the spectrum from the key illumination accompanying the mixed schedule and from the positive discriminative stimulus. When the magnitude of the difference between the latter two stimuli (salience) was varied, more pecks occurred on the observing key producing the larger of the two differences than on the key producing the smaller difference. In the second experiment, the stimulus accompanying the mixed schedule was at the far end of the spectrum, and the magnitude of the difference between the two discriminative stimuli (disparity) was varied. The proportion of pecks occurring on each observing key shifted systematically in the direction of the key producing the larger difference. The salience of the discriminative stimuli and their disparity each has an independent influence on the frequency of observing when the other is controlled, but the effect of the salience appears to be the more substantial.     

Local contrast in multiple schedules: the effect of stimulus discriminability.

A three-ply multiple schedule assessed responding in a standard component as a function of the just-preceding schedule. The principal experimental condition was the difference among the wavelengths signaling the schedule components. Only the pigeons working in a narrow wavelength range showed persistent positive local contrast; that is, response rate during the standard component was higher when that component followed extinction than when it followed itself. Birds in both narrow- and medium-range groups showed persistent negative local contrast; that is, rate was lower following a relatively rich component. The dissipation of positive contrast appeared to be most clearly related to the establishment of differential responding. Negative contrast was inversely related to wavelength differences. Theories pertaining to contrast must account for the role of discrimination in both positive and negative types.     

Choice between response units: The rate constancy model

In a conjoint schedule, reinforcement is available simultaneously on two or more schedules for the same response. The present experiments provided food for key pecking on both a random-interval and a differential-reinforcement-of-low-rate (DRL) schedule. Experiment 1 involved ordinary DRL schedules; Experiment 2 added an external stimulus to indicate when the required interresponse time had elapsed. In both experiments, the potential reinforcer frequency from each component was varied by means of a second-order fixed-ratio schedule, and the DRL time parameter was changed as well. Response rates were described by a model stating that time allocation to each component matches the relative frequency of reinforcement for that component. When spending time in a given component, the subject is assumed to respond at the rate characteristic of baseline performance. This model appeared preferable to the absolute-rate version of the matching law. The model was shown to be applicable to multiple-response concurrent schedules as well as to conjoint schedules, and it described some of the necessary conditions for response matching, undermatching, and bias. In addition, the pigeons did not optimize reinforcer frequency.     

Experimental analysis of academic performance in a classroom setting

We evaluated the effects of specific stimulus prompts on accuracy of academic performance with adolescents who displayed academic problems in a public special education classroom. We conducted analyses of instructional strategies within a multielement design with two students who had mild disabilities. Differential effects of the strategies on reading comprehension were not apparent on demand (independent-level) tasks but were apparent on high-demand (instructional-level) tasks. These results suggested that the application of experimental analysis methodologies to instructional variables may facilitate the identification of stimulus prompts associated with accurate academic performance.     

Office paper recycling: A function of container proximity

We investigated the effects of proximity of containers on pounds of office paper recycled and not recycled by 25 employees. During a memo and central container condition, one container for recyclable paper was provided; in a memo and local container condition, desktop recycling bins, announced by memo, were successively introduced across administrative, office, and instructional settings using a multiple baseline design. Only 28% of paper was recycled in the central container condition, but when recycling containers were placed in close proximity to participants, 85% to 94% of all recyclable paper was recycled. Follow-up assessments, conducted 1, 2, 3, and 7 months after all settings received local recycling containers, showed that 84% to 98% of paper was recycled. Providing desktop recycling containers was a cost-effective procedure with long-term maintenance and program survival.