A procedure for generating differential "sample" responding without different exteroceptive stimuli

Sidman (1994, 2000) suggested that responses as well as stimuli can join equivalence classes, a hypothesis difficult to test because differential responding typically requires different stimuli. The present experiments describe a procedure with pigeons that avoids this potential confounding effect. In Experiment 1, spacing two responses 3 s apart (a differential-reinforcement-of-low-rate [DRL] schedule) to a white stimulus on some trials produced food or the comparison stimuli in a matching task, whereas pecking 10 or more times with no temporal restrictions (a fixed-ratio [FR] schedule) produced the same effect on other trials. Completing the alternative (unscheduled) requirement terminated the white stimulus and repeated the trial. Following such errors, pigeons learned to switch to the alternative response pattern on the repeat trials. In addition, the correct response pattern functioned as a conditional cue for comparison choice. In Experiment 2, mixed DRL-FR training was preceded by two-sample/two-alternative matching-to-sample with DRL and FR sample-response requirements. In a subsequent transfer test in which the correct response pattern to white served as the sample, pigeons preferentially chose the comparison previously reinforced following that pattern in the baseline task. This "unsignaled response" procedure may be useful for assessing whether differential responses can be members of acquired equivalence classes.     

Social influence in pigeons (Columba livia): the role of differential reinforcement

Socially-influenced learning was studied in observer pigeons that observed a demonstrator in an adjacent chamber performing a target response comprising standing on a box and pecking a key 10 times. In Experiment 1 there was no evidence for social learning in the absence of reinforcement of the observer's behavior. When the target response was already established in the observer's repertoire, but was not differentially reinforced in relation to the demonstrator's behavior, rates of extinction were not influenced by the demonstrator's behavior (Experiment 2). Reinforcement of the observer's target response in the presence of the modeled target response, and not in its absence, resulted in control of the observer's responding by the behavior of the demonstrator (Experiments 3 and 4). This control was extended in Experiment 5 to deferred responses that occurred following a delay since the demonstrator's target responses. The acquisition of social influence depended on differential reinforcement of the observer's target response, with the demonstrator's target behavior serving as the explicit discriminative stimulus.     

Transfer of specific contextual functions to novel conditional discriminations

Three adolescents and 4 children participated in studies designed to examine contextually controlled conditional discrimination performance. In Study 1, participants selected Comparison B1 in the presence one stimulus (A1) and Comparison B2 in the presence of another stimulus (A2) using a matching-to-sample procedure. Next, contextual stimuli X1 or X2 were presented, such that in the presence of X1, selection of B1 given A1 and selection of B2 given A2 were reinforced; and in the presence of X2, selection of B2 given A1 and selection of B1 given A2 were reinforced. Then, new conditional discriminations were taught with Stimuli E and F. When the contextual Stimuli X1 and X2 were presented, participants selected the same comparisons as previously established in the EF relations in the presence of X1, but the opposite comparison as in the EF relations in the presence of X2. The results then were replicated with new Stimuli G and H. In Study 2, a new conditional discrimination, CD, was taught. Then, four combinations of two-element samples--C1 and D1, C2 and D2, C1 and D2, or C2 and D1--were presented with X1 and X2 as comparisons. Five of 6 participants selected X1 in the presence of C1 and D1 or C2 and D2, and selected X2 in the presence of C1 and D2 or C2 and D1. Finally, in Study 3, two new discriminations IJ and JK were taught. Then, the transitive IK relations were tested with X1 and X2 as contextual stimuli. The 4 participants selected K1 in the presence of I1 and K2 in the presence of I2 when the contextual stimulus was X1--demonstrating class formation--and selected the other comparisons when the contextual stimulus was X2. These results suggest that the contextual control functions of X1 and X2 transferred even to relations that had not been directly taught. These results extend those demonstrating generalized contextual control by showing transfer of functions of the contextual stimuli in transitivity tests and when the former contextual stimuli were presented as comparisons.     

Uncovering the richness of the stimulus: structure dependence and indirect statistical evidence

The poverty of stimulus argument is one of the most controversial arguments in the study of language acquisition. Here we follow previous approaches challenging the assumption of impoverished primary linguistic data, focusing on the specific problem of auxiliary (AUX) fronting in complex polar interrogatives. We develop a series of corpus analyses of child-directed speech showing that there is indirect statistical information useful for correct auxiliary fronting in polar interrogatives and that such information is sufficient for distinguishing between grammatical and ungrammatical generalizations, even in the absence of direct evidence. We further show that there are simple learning devices, such as neural networks, capable of exploiting such statistical cues, producing a bias toward correct AUX questions when compared to their ungrammatical counterparts. The results suggest that the basic assumptions of the poverty of stimulus argument may need to be reappraised.     

Motivational influences on performance maintained by food reinforcement

In Study 1, we examined the independent effects of reinforcer consumption during sessions and meal consumption prior to sessions on performance maintained by food reinforcement. Nine individuals with developmental disabilities participated. On alternate days, a preferred edible item was delivered during (a) seven sessions conducted before lunch (repeated-reinforcement condition) versus (b) one session each conducted before and after lunch (pre- and postmeal conditions). Results for 7 of 9 participants showed decreased response rates across sessions in the repeated-reinforcement condition; results for 3 of 9 participants showed decreased rates during postmeal relative to premeal conditions. Two participants who did not show a decrement in responding during either comparison participated in Study 2, in which reinforcer consumption during sessions, combined with meal consumption prior to sessions, also had no effect on their performance. In Study 3, we determined whether (a) choice of reinforcers, (b) increased break time between sessions, (c) varied reinforcers, or (d) intermittent reinforcement schedules mitigated the satiation effects observed for the 7 participants in Study 1. Presession choice of reinforcers resulted in maintained performance for 2 of 6 participants exposed to this condition. Varied reinforcement resulted in maintained performance for only 1 of 5 participants exposed to this condition. Neither the increased break between sessions nor the intermittent reinforcement schedule was effective in maintaining performance for the participants who were exposed to these conditions.     

Associative symmetry in the pigeon after successive matching-to-sample training

If an organism is explicitly taught an A→B association, then might it also spontaneously learn the symmetrical B→A association? Little evidence attests to such “associative symmetry” in nonhuman animals. We report for the first time a clear case of associative symmetry in the pigeon. Experiment 1 used a successive go/no go matching‐to‐sample procedure, which showed all of the training and testing stimuli in one location and intermixed arbitrary and identity matching trials. We found symmetrical responding that was as robust during testing (B→A) as during training (A→B). In Experiment 2, we trained different pigeons using only arbitrary matching trials before symmetry testing. No symmetrical responding was found. In Experiment 3, we trained other pigeons with only arbitrary matching trials and then tested for symmetry. When these pigeons, too, did not exhibit symmetrical responding, we retrained them with intermixed identity and arbitrary matching trials. Less robust symmetrical responding was obtained here than in Experiment 1. Collectively, these results suggest that identity matching may have to be learned concurrently with arbitrary matching from the outset of training for symmetry to emerge.     

Infant perceptual and conceptual categorization: the roles of static and dynamic stimulus attributes

Infants' categorization of animals and vehicles based on static vs. dynamic attributes of stimuli was investigated in five experiments (N=158) using a categorization habituation-of-looking paradigm. In Experiment 1, 6-month-olds categorized static color images of animals and vehicles, and in Experiment 2, 6-month-olds categorized dynamic point-light displays showing only motions of the same animals and vehicles. In Experiments 3, 4, and 5, 6- and 9-month-olds were tested in an habituation-transfer paradigm: half of the infants at each age were habituated to static images and tested with dynamic point-light displays, and the other half were habituated to dynamic point-light displays and tested with static images. Six-month-olds did not transfer. Only 9-month-olds who were habituated to dynamic displays showed evidence of category transfer to static images. Together the findings show that 6-month-olds categorize animals and vehicles based on static and dynamic information, and 9-month-olds can transfer dynamic category information to static images. Transfer, static vs. dynamic information, and age effects in infant categorization are discussed.     

Reinforcing efficacy of food on performance during pre- and postmeal sessions

Assessments were conducted to identify preferred foods for 9 adults with severe to profound mental retardation. Subsequently, the reinforcing effects of each participant's most highly preferred food were evaluated during sessions conducted before and after lunch. Results showed that 4 participants' response rates were higher during premeal sessions than during postmeal sessions. By contrast, pre- and postmeal response rates were indistinguishable for the other 5 participants. These results indicate that the reinforcing efficacy of food may (but does not necessarily) diminish following meals and suggest that the influence of meal schedules should be examined on an individual basis when food is used as reinforcement during training sessions.     

Stability of functional equivalence and stimulus equivalence: effects of baseline reversals

Functional equivalence and stimulus equivalence classes were established, reversed, and tested for stability with college students. Functional stimulus classes were established using a task in which students were trained to say nonsense words in the presence of arbitrarily assigned sets of symbols. Computer-controlled speech-recognition technology was used to record and analyze students' vocal responses for accuracy. After the establishment of stimulus classes was demonstrated with a transfer-of-function test, the effects of reversing selected baseline simple discriminations were assessed during an additional transfer-of-function test and a follow-up test that occurred several weeks later. With the same students, stimulus equivalence classes were established and demonstrated with computerized matching-to-sample procedures. The effects of reversing selected baseline conditional discriminations also were assessed during a postreversal equivalence test and a follow-up test. Both functional stimulus classes and stimulus equivalence were sensitive to contingency reversals, but the reversals with stimulus equivalence closses affected stimulus class organization whereas reversals with functional stimulus classes did not. Follow-up performances were largely consistent with the original baseline contingencies. The similarities and differences between stimulus equivalence and functional equivalence are related to the specific contingencies that select responding in the presence of the stimuli that form the classes.     

Contextual control of stimulus generalization and stimulus equivalence in hierarchical categorization

The purpose of this study was to determine whether hierarchical categorization would result from a combination of contextually controlled conditional discrimination training, stimulus generalization, and stimulus equivalence. First, differential selection responses to a specific stimulus feature were brought under contextual control. This contextual control was hierarchical in that stimuli at the top of the hierarchy all evoked one response, whereas those at the bottom each evoked different responses. The evocative functions of these stimuli generalized in predictable ways along a dimension of physical similarity. Then, these functions were indirectly acquired by a set of nonsense syllables that were related via transitivity relations to the originally trained stimuli. These nonsense syllables effectively served as names for the different stimulus classes within each level of the hierarchy.