Representation of serial order in pigeons (Columba livia)

In Experiment 1, 2 groups of pigeons were trained to respond to either a 4-item (A→B→C→D) or 5-item (A→B→C→D→E) list. After learning their respective list, half of the subjects were trained on a positive pair with reinforcement provided when pairs were responded to in the order true to that of the original sequence (4-item: B→C; 5-item: B→D). The remaining subjects were trained on a negative pair with reinforcement provided for responding to the pairs in the order opposite to that learned in the original sequence (4-item: C→B; 5-item: D→B). Subjects in the positive pair condition learned their respective pair faster than did subjects in the negative pair condition. In Experiment 2, after reaching criterion on a 4-item list, subjects received 16 BC probe trials spread across 4 sessions of training. Subjects performed significantly above chance on the probe trials. The performance of our subjects in Experiments 1 and 2 demonstrates that, similar to monkeys, pigeons form a representation of the lists that they learn.     

Establishing Functional Classes In A Chimpanzee (Pan troglodytes) With A Two-item Sequential-Responding Procedure

A 9-year-old female chimpanzee was trained on a two-item sequential-responding task. Attempts were made with successive-reversal training to establish functional classes. In Experiment 1, the subject was exposed to between-session successive-reversal training in which one of two pairs of stimuli was reversed, and transfer of reversal responding to the other pair was tested with nonreinforcement probe trials. She did not show transfer during the course of reversals. Stimulus control established in the original training was maintained on nonreinforcement probe trials. In Experiment 2, within-session reversals were introduced. She showed transfer from the initially reversed pair to the other. The results were consistent with Vaughan's (1988) results with pigeons on successive discriminations, which indicated the formation of functional classes. In Experiment 3, crossover and wild-card tests were conducted to clarify the stimulus control of sequential responding. The results suggested that the sequential responding was controlled only by the first stimulus of each pair. To establish control by both first and second stimuli, trial-unique stimuli or wild cards were substituted for one of the items of the lists in Experiment 4. Further transfer tests, in which stimuli for the two new pairs appeared, were also given to the subject. She successfully responded to these two merged lists and reversed the order as the result of reversal training.     

Establishing auditory stimulus control over an eight-member equivalence class via conditional discrimination procedures

Two eight-member equivalence classes of visual stimuli were established during three phases of a training program. In Phase 1, two training arrangements were compared. In one, 3 subjects were taught on different trials to select from a single pair of comparison stimuli (A1, A2) in response to eight sample stimuli that were trained in pairs (B1, B2; C1, C2; D1, D2; E1, E2). In the second arrangement, subjects were taught to select from four pairs of comparisons (B1, B2; C1, C2; D3, D2; E2, E2) in response to two samples (A1, A2). Training with the single pair of comparison stimuli resulted in the development of equivalence relations (B1C1, B2C2, D1B1, D2B2, B1E1, B2E2, C1D1, C2D2, C1E1, C2E2, D1E1, D2E2, and their reciprocals) between the sample stimuli without direct training of these relations. In the other training arrangement, these relations among the comparison stimuli developed in the performance of 1 subject only. In Phase 2, three new pairs of stimuli (F1, F2; G1, G2; H1, H2) were substituted for three of the original pairs (B1, B2; C1, C2; D1, D2) and the training arrangements for the groups were reversed. Following training, the performances that showed equivalence relations on the probes in the first phase also showed equivalence relations in the second phase. If such relations did not develop in the first phase, they did not do so in the second phase. In Phase 3, relations between stimuli across the two previous phases (e.g., B1F1, B2F2, B1G1, B2H2, C1F1, etc.) were investigated. The 4 subjects whose performances showed the development of these relations were taught to select one stimulus from each class (E1 and E2) in response to a verbal label (I1 and I2) and then were tested to see if the verbal label controlled responding to the remaining members of the class (e.g., I1A1, I2A2, I1B1, I2B2, etc.). For 3 subjects, this generalized control occurred; for the 4th, generalization occurred only after verbal training with a second pair of visual stimuli (F1 and F2). In retests several months later, these auditory-visual relations were found to be intact or, if not, were recovered without direct training.     

Pre-extinction of sensory preconditioned electrodermal activity

In the present study, sensory preconditioning of human electrodermal activity was demonstrated. In the first phase of the experiment, two pairs of neutral pictures of human faces were presented (A/B and C/D) sequentially. In the second phase, one picture of one pair was immediately followed by an electrocutaneous stimulus (B+), and one picture of the other pair was not (D-). In the third phase the other picture of each pair (A and C) was tested. The effect of A and C alone presentations (pre-extinction) between the first and the second phase was investigated. When only those participants that showed reliable B+/D- differentiation were considered, the extinction group did not show stronger conditioned electrodermal activity to A than to C, whereas the control group did. These findings suggest that sensory preconditioning of anticipatory/preparatory responding only occurs when the pre-conditioned stimulus (A) actually predicts the conditioned stimulus (B).     

Configural learning in two species of marsupial (Setonix brachyurus and Sminthopsis crassicaudata)

Four experiments examined the ability of quokkas (Setonix brachyurus) and fat-tailed dunnarts (Sminthopsis crassicaudata) to solve 2 configural tasks: transverse and negative patterning. Transverse patterning requires the simultaneous solution of 3 overlapping discrimination problems (A+ B-, B+ C-, C+ A-). Both species could solve the nonoverlapping (elemental) version of this task (U+ V-, W+ X-, Y+ Z-), but only dunnarts solved the transverse patterning task. Negative patterning requires conditioned responses to 2 stimuli when presented separately but not together (A+, B+, AB-). Both species formed a selective conditioned response to A+ and B+ stimuli and inhibited responding to a simple nonreinforced stimulus (C-), but only dunnarts successfully inhibited responding to the AB- compound to solve the negative patterning task. These experiments are the first to demonstrate configural learning in a marsupial.     

Maintained nodal-distance effects in equivalence classes

Twelve subjects were trained to select one of two stimuli from a pair (the B pair) when presented with one of two stimuli from another pair (the A pair), thus establishing two AB relations, A1-B1 and A2-B2. In a similar fashion, additional stimuli were used to establish BC, CD, and DE relations. Trials used to train all relations occurred in each session. Once performances were established, probe trials were introduced that tested for the emergence of untrained relations (e.g., B1-D1 or A1-E1). These emergent relations were categorized according to nodal distance (i.e., the number of stimuli across which transitivity would have to hold in order for the relation to emerge). For example, a test for A2-C2 crosses one node (B2), whereas a test for A1-E1 crosses three nodes (B1, C1, and D1). Only 2 of the subjects formed equivalence classes. The evocation of class-appropriate responding by each emergent-relation probe was an inverse function of nodal distance for all 12 subjects. In addition, performance on the originally trained relations was disrupted by the introduction of probes. The 2 subjects who exhibited equivalence classes were then trained to make different numbers of key presses in the presence of each of the four A and E stimuli. In a response-transfer test, the B, C, and D stimuli evoked the responses trained to the A and E stimuli in the same equivalence class. Likelihood of class-appropriate responses was an inverse function of nodal distance, and this pattern persisted across testing. Reaction times in the transfer test were an inverted U-shaped function of nodal distance. Because training of the baseline relations occurred concurrently and the B, C, and D stimuli were presented an equal number of times before the transfer test, the test performances illustrate effects of nodal distance that were not confounded by order or amount of experience with the stimuli. The results imply that ordered, sequential exposure to individual stimulus relations may facilitate the development of equivalence classes and that the relatedness of stimuli within an equivalence class is a relatively permanent inverse function of nodal distance.     

Effects of stimulus–stimulus short-term memory associations in a Simon-like task

The Simon effect refers to faster responding when an irrelevant stimulus location corresponds with the response to a relevant stimulus attribute than when it does not. We investigated whether a memory-based Simon-like effect would occur when the irrelevant spatial attribute was associated with the stimulus during a prior task. In a first task, an association between colour and location was formed by requiring participants to count the occurrences of two colour stimuli, each of which was always presented in a left or right location. In a second task, the colour stimuli were presented centrally and mapped to left and right keypresses, with the mapping being inconsistent or consistent with the prior colour-location associations. A Simon-like effect was evident at the start of the second task, with performance being better when the established colour–position associations were consistent with the colour–response mapping than when they were not. This result indicates that stimulus–stimulus short-term memory associations formed during the first task transferred to the second task. For the remainder of the second task, the data showed a more conservative speed–accuracy criterion for the inconsistent condition than for the consistent condition, though a processing efficiency measure suggested that the prior stimulus–stimulus short-term associations may also continue to directly influence performance. Results suggest that simple declarative knowledge, as represented by stimulus–stimulus STM links, exerts less persistent transfer effects than procedural knowledge as provided by stimulus–response STM links.     

Negative patterning is easier than a biconditional discrimination

Two groups of rats were trained for 50 days on different discriminations in a magazine approach paradigm. One group was trained with a negative patterning schedule and a positive patterning schedule concurrently: they received intermixed trials of A+, B+, AB-, C-, D-, CD+ (A, B, C, and D are four distinct stimuli; the plus sign denotes reinforcement with food, and the minus sign denotes nonreinforcement). The second group of rats was trained with the same four stimuli arranged as compounds and reinforced according to the biconditional schedule AB+, CD+, AC-, and BD-. The first group learned the positive patterning schedule much more quickly than the negative patterning schedule, but they learned the negative patterning schedule more effectively than the second group learned the biconditional schedule. The authors discuss the implications of these findings for models of stimulus representation.     

Effects of preliminary class membership on subsequent stimulus equivalence class formation

The present study examined the effects of including stimuli previously trained as members of functional classes or equivalence classes on subsequent equivalence class formation, and isolated the effects of preliminary training from those of the acquired function stimuli. Fifty-six adults were assigned to 1 of 5 conditions. The control group (CONT) received no preliminary training prior to the terminal phase. Participants in the other 4 groups learned two 3-member functional classes and two 3-member equivalence classes during the preliminary phase. The terminal equivalence phase trained two 5-member classes (A → B → C → D → E) comprising abstract forms; the C stimuli in the terminal phase were (a) from the preliminary functional classes for 1 group (ACQ-F), (b) from the preliminary equivalence classes for the second experimental group (ACQ-E), (c) pictures of everyday objects for the picture control group (PIC), and (d) novel, unfamiliar stimuli for the preliminary training control group (PRE-CONT). Class formation yields were 100% in the PIC condition and 11% in the CONT condition; however, low yields in the PRE-CONT, ACQ-F, and ACQ-E conditions were unexpected, suggesting that procedural variables in preliminary training account for more of the subsequent effects on class formation than the stimulus control properties of the acquired function stimuli.     

Testing response-stimulus equivalence relations using differential responses as a sample

This study tested the notion that an equivalence relation may include a response when differential responses are paired with stimuli presented during training. Eight normal adults learned three kinds of computer mouse movements as differential response topographies (R1, R2, and R3). Next, in matching-to-sample training, one of the response topographies was used to select a comparison stimulus B (B1, B2, or B3) conditionally upon presentation of sample stimulus A (A1, A2, or A3), and to select stimulus D (D1, D2, or D3) conditionally upon presentation of stimulus C (C1, C2, or C3). After two sample-comparison-response relations (ABR and CDR) were established, 18 sample-comparison relations were tested (BA, DC, RA, RB, RC, RD, AC, CA, AD, DA, BC, CB, BD, DB, AA, BB, CC, and DD). In the RA, RB, RC, and RD tests, the differential responses (R1, R2, and R3) were used as sample stimuli. All subjects made class-consistent comparison selections in the tests. This study provides evidence that responses may become members of an equivalence class.     

Sequential effects in auditory choice reaction time tasks

This paper concerns sequential effects in choice reaction time tasks. Performance in two interleaved auditory tasks was examined, and two general types of sequential effects were revealed. First, a response repetition effect occurred: Subjects were facilitated in responding when both the stimulus and the response were immediately repeated. Generally, it appeared that subjects were operating according to the bypass rule—that is, repeat the response if the stimulus or some aspect thereof is repeated from the preceding trial; otherwise, change the response. In addition, the experiment also revealed a second type of sequential effect, known as a task-switching effect. Subjects were overall slower to respond when the task changed between adjacent trials than when there was no task change. A final result was that subjects were markedly impaired when the stimulus changed but the same response had to be repeated. This finding has been reported elsewhere when purely visual tasks have been used. Hence, it seems that particular difficulties arise, in such sequential testing situations, when type-distinct stimuli are grouped into the same response categories.     

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.     

Six-member stimulus classes generated by conditional-discrimination procedures

In conditional-discrimination procedures with three sets of stimuli, A, B, and C, three stimuli per set (A1A2A3, B1B2B3, and C1C2C3), subjects (children and adults) learned to select Set-B and Set-C comparisons conditionally upon Set-A samples (A1B1, A1C1, A2B2, A2C2, A3B3, A3C3). If the conditional-discrimination procedures also generated equivalence relations, three 3-member stimulus classes would be demonstrable, A1B1C1, A2B2C2, and A3B3C3. In addition to these three sets, the present experiments used three other sets of stimuli--D, E, and F. The subjects learned to select Set-E and Set-F comparisons conditionally upon Set-D samples (D1E1, D1F1, D2E2, D2F2, D3E3, D3F3). This established a second group of three 3-member stimulus classes, D1E1F1, D2E2F2, and D3E3F3. In all, two groups of three 3-member classes were established by teaching subjects 12 conditional discriminations. The two groups of 3-member classes were then combined (successfully for 5 of 8 subjects) into a single group of three 6-member classes by teaching the subjects three more conditional relations (E1C1, E2C2, and E3C3). With three other children, enlarging the classes one member at a time also produced 6-member classes. As a consequence of class formation, 60 untrained conditional relations emerged from 15 that had been explicitly taught. Six of the subjects also proved capable of naming the stimuli consistently in accord with their class membership, but two subjects demonstrated class formation even in the absence of consistent naming.     

Sequential responding and planning in capuchin monkeys (Cebus apella)

Previous experiments have assessed planning during sequential responding to computer generated stimuli by Old World nonhuman primates including chimpanzees and rhesus macaques. However, no such assessment has been made with a New World primate species. Capuchin monkeys (Cebus apella) are an interesting test case for assessing the distribution of cognitive processes in the Order Primates because they sometimes show proficiency in tasks also mastered by apes and Old World monkeys, but in other cases fail to match the proficiency of those other species. In two experiments, eight capuchin monkeys selected five arbitrary stimuli in distinct locations on a computer monitor in a learned sequence. In Experiment 1, shift trials occurred in which the second and third stimuli were transposed when the first stimulus was selected by the animal. In Experiment 2, mask trials occurred in which all remaining stimuli were masked after the monkey selected the first stimulus. Monkeys made more mistakes on trials in which the locations of the second and third stimuli were interchanged than on trials in which locations were not interchanged, suggesting they had already planned to select a location that no longer contained the correct stimulus. When mask trials occurred, monkeys performed at levels significantly better than chance, but their performance exceeded chance levels only for the first and the second selections on a trial. These data indicate that capuchin monkeys performed very similarly to chimpanzees and rhesus monkeys and appeared to plan their selection sequences during the computerized task, but only to a limited degree.     

Class-consistent Differential Reinforcement And Stimulus Class Formation In Pigeons

Match-to-sample training clusters of A1 (sample): B1/B2 (comparisons), A2: B2/B1, B1: A1/A2, B2: A2/A1, B1: C1/C2, B2: C2/C1, C1: B1/B2, and C2: B2/B1 were presented to pigeons with class-consistent differential reinforcement using two dissimilar types of food reinforcers. Distinctive class-consistent response patterns occurred to the samples during the fixed-ratio 5 sample observing response requirement. Subsequent tests, modeled from the equivalence class paradigm demonstrated the emergence (80% class consistent) of the transitive-like A-C and C-A relations for 4 and 2 of 12 pigeons, respectively, and a strong trend (over 70%) for 7 and 6 others, respectively; the emergence of the reflexive-like identity relation when the nonidentical comparison was from the other class; and the disruption of the trained within-class relation with the addition of a reflexive comparison. After directional training of C1: D1/D2 and C2: D2/D1, tests indicated no emergence of the symmetric-like D-C relation or the composite D-B and D-A relations, but the B-D and A-D transitive-like relation occurred with some pigeons. Off-baseline training with class-consistent differential reinforcement contingent on responding to the D stimuli alone produced distinctive responding and, in turn, a trend to D-C symmetric-like control in 4 of 12 pigeons, as well as a shift toward class-consistent control on D-B and D-A test trials. Class-consistent differential reinforcement that produced distinctive sample behavior promoted stimulus control relations like those that circumscribe equivalence class formation. Respondent—operant interactions permit an analysis of the possible enrollment of stimulus values of distinctive responding to the discriminative stimuli forming the stimulus classes via processes corresponding to naming in humans.     

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.     

Factors impacting emergence of behavioral control by underselected stimuli in humans after reduction of control by overselected stimuli

Stimulus overselectivity occurs when only one of potentially many aspects of the environment controls behavior. Adult participants were trained and tested on a trial-and-error discrimination learning task while engaging in a concurrent load task, and overselectivity emerged. When responding to the overselected stimulus was reduced by reinforcing a novel stimulus in the presence of the previously overselected stimulus in a second trial-and-error discrimination task, behavioral control by the underselected stimulus became stronger. However, this result was only found under certain circumstances: when there was substantial overselectivity in the first training phase; when control by the underselected stimulus in the first phase was particularly low; and when there was effective reduction in the behavioral control exerted by the previously overselected stimuli. The emergence of behavioral control by the underselected stimulus suggests that overselectivity is not simply due to an attention deficit, because for the emergence to occur, the stimuli must have been attended to and learned about in the training phase; but that a range of additional learning factors may play a role.     

“TRANSITIVE INFERENCE” IN MULTIPLE CONDITIONAL DISCRIMINATIONS

We used multiple conditional discriminations to study the inferential abilities of pigeons. Using a five-term stimulus series, pigeons were trained to respond differentially to four overlapping pairs of concurrently presented stimuli: A+B?, B+C?, C+D?, and D+E?, where plus and minus indicate the stimulus associated with reinforcement and extinction, respectively. Transitive inference in such situations has been defined as a preference for Stimulus B over Stimulus D in a transfer test. We measured this and other untrained preferences (A vs. C, A vs. D, B vs. E, etc.) during nonreinforced test trials. In three experiments using a novel, rapid training procedure (termed autorun), we attempted to identify the necessary and sufficient conditions for transitive inference. We used two versions of autorun: response-based, in which the subject was repeatedly presented with the least well-discriminated stimulus pair; and time-based, in which the subject was repeatedly presented with the least-experienced stimulus pair. In Experiment 1, using response-based autorun, we showed that subjects learned the four stimulus pairs faster than, but at a level comparable to, a previous study on transitive inference in pigeons (Fersen, Wynne, Delius, & Staddon, 1991), but our animals failed to show transitive inference. Experiments 2 and 3 compared time- and response-based autorun. Discrimination performance was maintained, but transitive inference was observed only on the second exposure to the response-based procedure. These results show that inferential behavior in pigeons is not a reliable concomitant of good performance on a series of overlapping discriminations. The necessary and sufficient conditions for transitive inference in pigeons remain to be fully defined.     

Higher order autoshaping

A series of experiments is reported on appetitive higher order conditioning in the pigeon. Experiment I showed that second order autoshaping can be produced by pairing a neutral keylight with a keylight of another colour, previously paired with food. Experiment II employed an omission procedure to show that second order autoshaping is a consequence of the contingency between first and second order stimuli. In Experiment III, extinction of responding to the first order stimulus was shown to reduce responding to the second order stimulus. Experiments IV and V showed firstly that this reduction is not due to generalization of extinction, and secondly that second order key pecks may be produced in the absence of any pecking to the first order stimulus. The results suggest that second order autoshaping is based largely on a direct association between the first and second order stimuli.     

A transfer of functions through derived arbitrary and nonarbitrary stimulus relations

During Experiments 1 and 2, subjects were trained in a series of related conditional discriminations in a matching-to-sample format (A1-B1, A1-C1 and A2-B2, A2-C2). A low-rate performance was then explicitly trained in the presence of B1, and a high-rate performance was explicitly trained in the presence of B2. The two types of schedule performance transferred to the C stimuli for all subjects in both experiments, in the absence of explicit reinforcement through equivalence (i.e., C1 = low rate and C2 = high rate). In Experiment 2, it was also shown that these discriminative functions transferred from the C1-C2 stimuli to two novel stimuli that were physically similar to the C stimuli (SC1 and SC2, respectively). For both these experiments, subjects demonstrated the predicted equivalence responding during matching-to-sample equivalence tests. In Experiments 3 and 4, the conditional discrimination training from the first two experiments was modified in that two further conditional discrimination tasks were trained (C1-D1 and C2-D2). However, for these tasks the D stimuli served only as positive comparisons, and ND1 and ND2 stimuli served as negative comparisons (i.e., C1 × ND1 and C2 × ND2). Subsequent to training, the negatively related stimuli (ND1 and ND2) did not become discriminative for the schedule performances explicitly trained in the presence of B1 and B2, respectively. Instead, the ND1 stimulus became discriminative for the schedule performance trained in the presence of B2, and ND2 became discriminative for the schedule performance trained in the presence of B1. All subjects from Experiment 4 showed that the novel stimulus SND1, which was physically similar to ND1, became discriminative for the same response pattern as that controlled by ND1. Similarly, SND2, which was physically similar to ND2, became discriminative for the same response pattern as that controlled by ND2. Subjects from both Experiments 3 and 4 also produced equivalence responding on matching-to-sample equivalence tests that corresponded perfectly to the derived performances shown on the transfer of discriminative control tests.