Further Investigation of Responding Elicited by BC and C After A+, AB-, ABC+ Training

Two experiments with pigeons explored conditioned keypeck responding to new visual targets after visual compound discrimination training. In the first experiment, pigeons were trained with an A+, AB-, ABC+, AD-, ADC+ task, in which stimulus A signalled food, stimulus compounds AB and AD signalled no food, and stimulus compounds ABC and ADC signalled food. According to both an elemental model (Rescorla & Wagner, 1972) and a configural model (Pearce, 1987) of Pavlovian conditioning, test compounds BC and DC should elicit less responding than should C alone. However, the birds responded more to BC and DC than to C. In the second experiment, another set of pigeons was trained with an A+, AB-, ABC+, AD-, ADE+ task, in which stimulus A signalled food, stimulus compounds AB and AD signalled no food, and stimulus compounds ABC and ADE signalled food. Contrary to the prediction of the Rescorla-Wagner model, keypeck responding was not less on BC and DE trials than on C and E trials in testing. However, B and D attenuated responding to E and C, respectively, when presented in compounds BE and DC. The Pearce model was able to accommodate these results.     

Similarity and Discrimination Learning

The role played by similarity in discrimination learning was examined in four experiments using compound stimuli. In Experiment 1, pigeons received training in which food was presented after stimulus A, compound AB, but not compound ABC—A+ BC+ ABCo. The A+ ABCo discrimination was acquired more readily than was the BC+ ABCo discrimination. In the remaining experiments, training was of the form, A+ B+ C+ AB+ AC+ BC+ ABCo. The discrimination between the single stimuli A+ B+ C+ and ABCo consistently developed more readily than between the pairs of stimuli AB+ AC+ BC+, and ABCo. The results are shown to be more consistent with a configural than with an elemental theory of conditioning.     

Effects of discrimination training on responding during a compound conditioned stimulus.

Four experiments examined responding in the presence of a triple-element compound ABC after discrimination training in which 2 compounds, AB and BC, signaled the delivery of food and 1 element alone, B, signaled the absence of food. In Experiments 1 and 2, using rats, responding during ABC was more vigorous than in a control group for which A and C but not B had been individually paired with food. This finding was replicated in Experiment 3, which used pigeons, and in Experiment 4, where all 3 stimuli of the control condition were individually paired with food. The results are more consistent with a configural than with an elemental theory of learning.     

Overshadowing and associability change

Three appetitive Pavlovian conditioning experiments with rats examined the associability of stimuli A and B that had a history of compound conditioning (AB+), relative to stimuli X and Y that had a history of conditioning in isolation (X+, Y+). Following this training, Experiment 1 revealed that conditioned responding was higher to X and Y than to A and B (overshadowing). In a subsequent AY+, AX-, BY- test discrimination, the AY/BY discrimination was solved more readily than the AY/AX discrimination. In Experiment 2, following AB+, X+, Y+ training, A and Y were presented as a compound and signaled the availability of reinforcement upon the performance of an instrumental response. Test trials in which A and Y were presented alone, and in extinction, revealed that A acquired greater control of instrumental responding than Y. Experiment 3 revealed that following AB+, X+, Y+ training, A and B served as more effective discriminative stimuli for instrumental responding than X and Y. Overall, these results imply that the associability of stimuli conditioned in compound is higher than stimuli conditioned in isolation. These results are discussed in terms of attentional theories of associative learning.     

Summation: Further assessment of a configural theory

Rats received Pavlovian conditioning in which food was signalled by a visual stimulus, A+, an auditory stimulus, B+, and a compound composed of different visual and auditory stimuli, CD+. Test trials were then given with the compound AB. Experiments 1 and 2A revealed stronger responding during AB than during CD. In Experiment 2B, there was no evidence of a summation of responding during AB when A+ B+ training was conducted in the absence of CD+ trials. A further failure to observe abnormally strong responding during ABwas found in Experiment 3 for which the training trials with A+ B+ CD+ were accompanied by trials in which C and D were separately paired with food. The results are explained in terms of a configural theory of conditioning, which assumes that responding during a compound is determined by generalization from its components, as well as from other compounds to which it is similar.     

Changes in cue associability across training in human causal learning

A series of experiments studied the amount learned about two food cues (A and B) whose presentation in a meal was followed by an allergy (+) in a fictitious patient. Participants were trained with A+ and C+ in Phase 1 and then with AB+ or AB++ in Phase 2. Subsequent testing revealed that BC was more allergenic than AD, showing that more had been learned about B than A in Phase 2. Participants were also trained with A+, then with AB+, and finally with AB++. The results of interpolating AB+ between A+ and AB++ training were consistent with the hypothesis that pretraining with Cue A selectively suppressed attention to its associate across the AB+ trials and, thereby, reduced the amount subsequently learned about B on AB++ trials.     

A modified version of the unique cue theory accounts for olfactory compound processing in honeybees

We investigated the capability of honeybees to discriminate between single odorants, binary olfactory mixtures, and ternary olfactory mixtures in olfactory conditioning of the proboscis extension reflex. In Experiment 1, three single odorants (A+, B+, and C+) and three binary mixtures of these odors (AB+, AC+, and BC+) were reinforced while the ternary compound, consisting of all three odors (ABC-), was nonreinforced. In Experiment 2, only one single odorant (A+) and one binary olfactory compound (BC+) were reinforced while the ternary compound (ABC-) consisting of the single odor and the binary compound was nonreinforced. We studied whether bees can solve these problems and whether the course of differentiation can be predicted by the unique cue theory, a modified unique cue theory, or Pearce's configural theory. Honeybees were not able to differentiate reinforced from nonreinforced stimuli in Experiment 1. However, summation to ABC observed at the beginning of training contradicts the predictions of Pearce's configural theory. In Experiment 2, differentiation between the single odorant A and the ternary compound developed more easily than between the binary compound BC and ABC. This pattern of differentiation is in line with a modified unique cue theory and Pearce's configural theory. Summation to ABC at the beginning of training, however, again was at odds with Pearce's configural theory. Thus, olfactory compound processing in honeybees can best be explained by a modified unique cue theory.     

Elemental versus configurai models of categorization in children and adults

In experiment 1, 7-and 8-year-old children learned to classify six features, A–F, as belonging to one of two artificial categories, or to neither category. Feature A and the compound BC were designated as members of Category 1, the compounds DE and EF were members of category 2, while D alone and the compound AB, belonged to neither category. Following successful learning, the participants were asked to rate two groups of test features, ABC and DEF, as likely members of their respective categories. Participants' certainty ratings of the categorization of the compound DEF were greater than for the compound ABC. Experiment 2 replicated the results of experiment 1 with adult participants. These data are at odds with predictions from an elemental associative theory, that suggested by Rescorla and Wagner (1972), which assumes that category judgements are made on the basis of associations between individual features and a category.     

Elemental versus configurai models of categorization in children and adults

In experiment 1, 7-and 8-year-old children learned to classify six features, A–F, as belonging to one of two artificial categories, or to neither category. Feature A and the compound BC were designated as members of Category 1, the compounds DE and EF were members of category 2, while D alone and the compound AB, belonged to neither category. Following successful learning, the participants were asked to rate two groups of test features, ABC and DEF, as likely members of their respective categories. Participants' certainty ratings of the categorization of the compound DEF were greater than for the compound ABC. Experiment 2 replicated the results of experiment 1 with adult participants. These data are at odds with predictions from an elemental associative theory, that suggested by Rescorla and Wagner (1972), which assumes that category judgements are made on the basis of associations between individual features and a category.     

The effects of using stimuli from three different dimensions on autoshaping with a complex negative patterning discrimination

In two experiments pigeons received a complex negative patterning discrimination, using autoshaping, in which food was made available after three stimuli if they were presented alone (A, B, C), or in pairs (AB, AC, BC), but not when they were all presented together (ABC). Subjects also received a positive patterning discrimination in which three additional stimuli were not followed by food when presented alone (D, E, F), or in pairs (DE, DF, EF), but they were followed by food when presented together (DEF). Stimuli A and D belonged to one dimension, B and E to a second dimension, and D and F to a third dimension. For both problems, the discrimination between the individual stimuli and the triple-element compounds developed more readily than that between the pairs of stimuli and the triple-element compound. The results are consistent with predictions that can be derived from a configural theory of conditioning.     

Effect of observing response requirements to sample and comparison stimuli on the establishment of reject control (sample/S- relations)

The establishment of sample/S- relations (or reject control) during conditional discrimination training (AB, BC) affects transitivity (AC), equivalence (CA) and reflexivity (AA, BB, CC) test outcomes. The present study parametrically evaluated the effects of different observing patterns to comparison stimuli on the establishment of reject control during baseline conditional relation training. A matching-to-sample with observing requirements (MTS-OR) procedure was implemented during AB and BC conditional discrimination training. During training, the participants were required to observe the sample and incorrect comparison on every trial before responding. In addition, the participants were divided into three groups that differed regarding the percentage of training trials on which they were prevented from observing the correct comparison stimuli: 25%, 50%, and 75%. Once the mastery criteria were achieved during training, transitivity (AC), symmetry (BA, CB), equivalence (CA), and reflexivity (AA, BB, CC) tests were conducted with all comparison stimuli visible from the beginning. The results suggest that the number of errors during transitivity, equivalence, and reflexivity tests progressively increased as participants were prevented from observing the correct comparison on a greater number of trials during training. Symmetry test results, however, were not affected by the experimental manipulation. Moreover, the number of participants showing reject-control patterns during tests slightly increased and the number of participants showing select-control patterns decreased as a function of the number of trials on which the participants were prevented from observing the correct comparison. Thus, we suggest that observing patterns during training is a relevant variable that affects equivalence test outcomes.     

Perceptual learning enhances retrospective revaluation of conditioned flavor preferences in rats

Forward and backward blocking of taste preference learning was compared in rats. In the forward condition, thirsty rats were exposed to a flavor (A) in sucrose solution (+) or in water (-), after which they were exposed to A in compound with another flavor (B) in sucrose solution (i.e., AB+). In the backward condition, these phases were reversed. Consumption of B alone was assessed when rats were food deprived. In the forward condition, rats given A+ consumed less B than rats given A-, providing evidence of forward blocking, whereas in the backward condition, rats given A+ drank more of B than those given A-. Subsequent experiments found that alternating but not blocked preexposure to A and B, when given prior to training, produced blocking of B whether A+ was given before or after AB+, suggesting that prior failures to observe backward blocking reflect failures of discrimination.     

Backward blocking in honeybees

Three experiments with foraging honeybees were designed to study the effect of experience with A on responding to B after AB+ training. In the first experiment, responding to B was the same whether the AB+ training was preceded or followed by A+ training. In the second experiment, responding to B after AB+ training was less in animals that also had A+ training than in control animals that were equally often reinforced in the absence of A; whether the A+ training preceded, was concurrent with, or followed the AB+ training made no difference. In the third experiment, responding to B after AB+ training was less when the AB+ training was followed by A+C- training than when it was followed by C+/A- training. These results, like those of some recent vertebrate experiments, take us beyond the traditional explanation of blocking in terms of impaired conditioning of B on AB+ trials and support the suggestion that the mechanism, still poorly understood, may nevertheless be a relatively simple one.     

Analysis of an ambiguous-feature discrimination

An autoshaping experiment with pigeons and three appetitive Pavlovian conditioning experiments with rats investigated the course of an ambiguous-feature discrimination in which trials with stimuli A and BC were followed by food, and trials with B and AC were not. The discrimination between A and B was acquired more rapidly than the discrimination between BC and AC in all experiments. Furthermore, the acquisition of conditioned responding with A was faster than that with BC for the three rat experiments. The results of these experiments are discussed in terms of elemental and configural theories of associative learning.     

Analysis of an ambiguous-feature discrimination

An autoshaping experiment with pigeons and three appetitive Pavlovian conditioning experiments with rats investigated the course of an ambiguous-feature discrimination in which trials with stimuli A and BC were followed by food, and trials with B and AC were not. The discrimination between A and B was acquired more rapidly than the discrimination between BC and AC in all experiments. Furthermore, the acquisition of conditioned responding with A was faster than that with BC for the three rat experiments. The results of these experiments are discussed in terms of elemental and configural theories of associative learning.     

Second-order conditioning in human predictive judgements when there is little time to think

Associative accounts uniquely predict that second-order conditioning might be observed in human predictive judgements. Such an effect was found for cue X in two experiments in which participants were required to predict the outcomes of a series of training trials that included P + and PX-, but only when training was paced by requiring participants to make a prediction within 3 s on each trial. In Experiment 1 training on P + ended before training was given on PX - . In Experiment 2 trials with P+, PX-, T + and other cues were intermixed. In the unpaced group inhibitory learning was revealed by a summation test, TX versus TM, where M was a control stimulus. These results suggest either that pacing interferes with learning successive associations more than with learning simultaneous associations or that lack of time to think interferes with inferential processes required for this type of inhibitory learning.     

Elemental and non-elemental olfactory learning in Drosophila

Brain complexity varies across many orders of magnitude between animals, and it is often assumed that complexity underpins cognition. It is thus important to explore the cognitive capacity of widely used model organisms such as Drosophila. We systematically investigated the fly’s ability to learn discriminations involving compound olfactory stimuli associated with shock. Flies could distinguish binary mixtures (AB+ CD-), including overlapping mixtures (AB+ BC-). They could learn positive patterning (AB+ A- B-) but could not learn negative patterning (A+ B+ AB-) or solve a biconditional discrimination task (AB+ CD+ AC- BD-). Learning about the elements of a compound (AB+) was not affected by prior conditioning of one of the elements (A+ AB+): flies do not exhibit blocking in this task. We compare these results with the predictions from simulation of several well-known theoretical models of learning, and find none are fully consistent with the overall pattern of observed behaviour.     

A new approach to the formation of equivalence classes in pigeons

Four pigeons were given simultaneous discrimination training with visual patterns arbitrarily divided into two sets, with the stimuli in one set designated A1, B1, C1, and D1 and those in the other set designated A2, B2, C2, and D2. In sequentially introduced training phases, the pigeons were exposed to a series of reversals to establish AB and then CD equivalences. In subsequent testing sessions, a subset of stimuli from one set served as positive stimuli and those from the other set as negative stimuli on training trials, and transfer of the reinforced relation to other members of the sets was tested with nonreinforced probe trials. The pigeons were trained further on AC and BD equivalences and then were tested for the emergence of untrained AD and BC equivalences. Two of the 4 pigeons exhibited the emergence of one of these untrained equivalences, evidence for the emergence of transitive relations. This finding suggests that the pigeons established three-member functional equivalence classes by incorporating separately trained multiple equivalence relations. Repeated reversal training and probe testing enabled us to explore the formation and expansion of functional equivalence classes in pigeons.     

Reading comprehension with the Go/No-Go procedure with compound stimuli

The present study investigated whether the Go/No-Go procedure with compound stimuli produces emergent relations among dictated words (A), pictures (B), and printed words (C) and the emergence of textual behavior (CD) using a multiple probe design across word sets. Three preschool children were exposed to 4 phases: (1) pretests for BC, CB, and CD relations, (2) pretraining with known stimuli, (3) AB and AC training, and (4) posttests for BC, CB, and CD relations. During AB and AC training, responses to A1B1, A2B2, A1C1, and A2C2 compound stimuli, but not to A1B2, A2B1, A1C2, and A2C1, were reinforced. The results showed that all participants met the learning criterion and demonstrated emergence of BC and CB relations (i.e., relations between pictures and printed words), and CD relations (i.e., textual behavior) after training. These results suggest that the Go/No-Go procedure with compound stimuli is an effective alternative for establishing reading comprehension.     

Attention in the pigeon: testing for excitatory and inhibitory control by the weak elements.

In two experiments, pigeons were trained on a successive discrimination between a color and either a compound S+ or a compound S- consisting of a form superimposed on a second color. Two stimulus control tests followed discrimination training: an attention test in which the form and colors used in training were presented singly and in combination, and then a resistance-to-reinforcement test using the form element of S+ or S- and a novel form. In the attention test, the birds trained with a compound S+ responded most to the S+ compound, less to the S+ color alone, and still less to the S+ form on a dark key. Few responses were made to the negative stimulus, either alone or with the S+ form added. The birds trained with a compound S- pecked most at the S+ color and to a compound of the S+ color with the S- form added. The resistance-to-reinforcement test showed that the birds trained with a compound S+ responded more to the S+ form than to a novel form. However, the birds trained with a compound S- did not reliably respond more to a novel form than to the S- form. These findings suggested that the form element of a compound S+ gains some excitatory control, but the form element of a compound S- does not acquire inhibitory control. The possibility existed that low levels of responding to the S+ form on a dark background in the first experiment were due to use of a darkened key to separate S+ and S- periods during discrimination training. However, the essential findings were the same in a second experiment in which darkening of the chamber separated S+ and S- periods.