A test of symmetry and transitivity in the conditional discrimination performances of pigeons

In a matching-to-sample context, pigeons were taught two conditional discriminations according to one of three equivalence paradigms: train if A, then select B and if B, then select C; train if B, then A and if B, then C; or train if A, then B and if C, then B. Test trials without reinforcement revealed that the conditional relations did not satisfy the symmetrical and transitive properties of an equivalence relation. Apparently, only specific if... then relations were learned. Contrary to Kendall's (1983) findings, and probably as a consequence of procedural differences, none of the pigeons in the present experiment were observed to emit mediating behavior during the transitivity probe trials. The absence of symmetry and transitivity may be related to the individual stimuli not being reflexive. Behavioral techniques other than the commonly used matching-to-sample technique might better succeed in avoiding unintended stimulus control in the study of the formation of stimulus classes.     

DOES CONDITIONAL DISCRIMINATION LEARNING BY PIGEONS NECESSARILY INVOLVE HIERARCHICAL RELATIONSHIPS?

Four experiments demonstrate that when putative conditional and discriminative cues are presented simultaneously in the single reversal procedure, it is not possible to ascribe a uniquely conditional or uniquely discriminative function to either of the cues. In Experiment 1, pigeons were trained to respond to a blue key and not to a red key while the houselight was on; then in a different session they learned the reversal of this discrimination with the houselight off (single reversal). Separate groups were tested for color generalization with houselight conditions alternating in blocks of trials or for houselight intensity generalization with blue and red key colors alternating in blocks of trials. Both test procedures revealed a conditional relationship between houselight and key color conditions. Experiment 2 produced the same result following training in which the key colors were held constant across training sessions while the houselight and no houselight conditions varied within sessions. In Experiment 3, separate groups were trained with the two procedures but were tested with randomly ordered combinations of key colors and houselight intensities. The two groups yielded indistinguishable bidimensional generalization gradients with peaks at both previously reinforced stimulus combinations. In Experiment 4 the subjects were switched from one of these training procedures to the other with no decrement in their discriminative performance. We conclude that for successive discriminations between conditional- and discriminative-stimulus combinations, the notion of a hierarchical relation between conditional and discriminative stimuli must be extended to include a symmetrical relationship or the notion should be abandoned altogether.     

Nonhumans have not yet shown stimulus equivalence

Recently, two published articles have reported finding stimulus equivalence in nonhumans. One suggested that equivalence was due to the mediation of names. The procedure used trained all components of all tested relations. Because nothing was derived, the defining characteristics of equivalence were not achieved. In the second study a definition of equivalence was proposed that fails to distinguish functional stimulus classes from equivalence classes. The resulting data are not clearly relevant to stimulus equivalence in Sidman's sense of the term. Stimulus equivalence has not yet been shown in nonhumans.     

Effectiveness and persistence of precurrent mediating behavior in delayed matching to sample and oddity matching with children.

Two kinds of mediating behavior were compared with respect to their effectiveness in variable-delay matching-to-sample and oddity-matching tasks. Each of four 5-year-old children was trained to emit either differential or common mediating responses. The differential mediating response consisted of pressing a specific computer key corresponding to either of two possible sample stimuli (a red or a green square). The common mediating response consisted of pressing one of the two response keys regardless of the sample. The differential-response subjects did not show the typical, delay-related decrease in matching-to-sample performance that characterized the behavior of common-response subjects. An oddity-matching task was then introduced, and subjects were instructed to use the mediating keys however they preferred, including not at all. Differential-response subjects continued to respond on the originally trained mediating keys in response to sample presentation and later reversed their choice responding, thus accommodating the oddity-matching requirements. Common-response subjects continued to emit the previously trained mediating response and experienced limited success in oddity matching. Results were interpreted in terms of stimulus control, instructional control, and experimental history.     

Independence of stimulus discriminability from absolute rate of reinforcement in a signal-detection procedure.

Three experiments are reported in which two pigeons were trained to detect differences in stimulus duration under varying levels of absolute rate of reinforcement. Two red stimuli, differing in duration, were arranged probabilistically on the center key of a three-key chamber. On completion of the center-key duration, the center keylight was extinguished and the two side keys were illuminated white. Correct responses were left-key pecks following the shorter duration and right-key pecks following the longer duration. In Experiment 1, relative rate of reinforcement for correct responses was held constant and absolute rate of reinforcement was varied in seven conditions from continuous reinforcement to a variable-interval 90-second schedule. In Experiment 2, relative rate of reinforcement was manipulated across three different absolute rates of reinforcement (continuous reinforcement, variable-interval 15-second, and variable-interval 45-second). Stimulus discriminability was unaffected by changes in absolute or relative rates of reinforcement. Experiment 3 showed that discriminability was also unaffected by arranging the same consequences (three-second blackout) for unreinforced correct responses and errors.     

Autoshaped key pecking maintained by access to a social space.

When four experimentally naive pigeons were exposed to occasional forward pairings of a keylight followed by a doorlight (that signaled access to a large social space), all subjects began to peck the lit key. In a second experiment, where the keylight either preceded the presentation of the doorlight or was presented independently of it, key pecking was maintained only in the former circumstance. The unconditioned stimulus in these experiments--arrival in the social space--did not elicit pecking. Hence, the conditioned response of key pecking and the unconditioned response of entering the social space differed. This demonstration of autoshaping with a social-space unconditioned stimulus argues against a stimulus-substitution account of the findings.     

Stimulus control of the pigeon's ability to peck a moving target.

Two pigeons were trained to peck whichever of eight keys displayed a white field (SD). The other seven keys displayed a white "X" on a black background (S delta). Each peck to SD produced three-second access to grain, a three-second intertrial interval (ITI), and the next trial. Pecks to S delta produced a three-second timeout (TO) and the same trial. During later sessions the key displaying SD changed every t seconds (t = 3, 2, 1, .5, and .25 sec), requiring the birds to track the position of the SD. Pecks on a ninth key increased t. Several sessions employed novel stimuli to ascertain the controlling stimulus dimensions. Both birds made few errors acquiring the original discrimination. During the tracking sessions, both birds made few errors when t = .5 sec. Only one reliably lengthened t. Data from sessions with novel stimuli indicate that color and form were important aspects of SD and S delta respectively; movement contributed to the final performance.     

MOTIVATING AUTISTIC CHILDREN THROUGH STIMULUS VARIATION

This study evaluated the differential effectiveness of two methods of presenting discrimination tasks when teaching autistic children. In a constant task condition, the common method of presenting a single task throughout a session was used. In a varied task condition, the same task was interspersed with a variety of other tasks from the children's clinic curricula. Results showed declining trends in correct responding during the constant task condition, with substantially improved and stable responding during the varied task condition. In addition, naive observers judged the children to be more enthusiastic, interested, happier, and better behaved during the varied task sessions. These results suggest that “boredom” may be a particularly important variable to control in the treatment of autistic children, and that particular care may be necessary when defining criteria for task acquisition. The results are discussed in relation to the literature on increased responsivity to stimulus novelty and variation.     

THE USE OF STIMULUS CONTROL OVER LITTERING IN A NATURAL SETTING

A conventional litter receptacle (55-gallon drum) and a specially designed receptacle consisting of a 55-gallon drum adorned with a plywood “hat” were alternated in two areas of a football stadium over a period of four games. A frequency count of several types of litter articles showed that more than twice as many items were deposited within the experimental container than the conventional one (an average of 52.5 and 21.5 items per game, respectively). The weight of litter deposited within each container showed a similar relationship. An average of 0.65 kg of litter per game were deposited within the conventional receptacle compared with an average of 1.3 kg per game for the experimental receptacle.