David W. Dickins

An fMRI study of stimulus equivalence.

In order to study brain activation during the formation of equivalence relations, 12 subjects underwent fMRI during matching-to-sample (MTS) tests of (1) previously trained arbitrary relationships between iconic stimuli and the untrained, emergent relations of (2) symmetry, (3) transitivity, and (4) symmetry with transitivity, plus a test of verbal fluency (VF). Brain activation was similar in all MTS tasks and in the VF task. In particular, both types of task activated dorsolateral prefrontal cortex (DLPFC) and posterior parietal cortex bilaterally. However VF, but not the MTS tasks, activated Brocas area. In three of the four MTS tasks, behavioural accuracy was significantly correlated with left lateralisation of DLPFC activity. Brain activation patterns during equivalence thus resembled those involved in semantic processing underlying language, without involving regions concerned with the simple sub-vocal articulation of stimulus names.

Influence of environmental manipulation on exploratory behaviour in male BDNF knockout mice

It is widely accepted that brain derived neurotrophic factor (BDNF) plays a crucial role in mediating changes in learning and memory performance induced by environmental conditions. In order to ascertain whether BDNF modulates environmentally induced changes in exploratory behaviour, we examined mice carrying a deletion in one copy of the BDNF gene. Young heterozygous male BDNF knockout mice (BDNF+/-) and their wild-type (WT) controls were exposed to the enriched environment condition (EC) or the standard condition (SC) for 8 weeks. Exploratory behaviour was assessed in the open-field (OF) and hole-board (HB) test. Brains from EC and SC reared animals were processed for Golgi-Cox staining and the dendritic spine density in the dentate gyrus (DG) and CA1 hippocampal regions were examined. We found behavioural differences both due to the genetic modification and the environmental manipulation, with the BDNF+/- mice being more active in the OF whereas the EC mice had increased exploratory behaviour in the HB test. Environmental enrichment also led to an increase in dendritic spines in the hippocampal CA1 region and DG of the wild-type mice. This effect was also found in the enriched BDNF+/- mice, but was less pronounced. Our findings support the critical role of BDNF in behavioural and neural plasticity associated with environmental enrichment and suggest that besides maze learning performance, BDNF dependent mechanisms are also involved in other aspects of behaviour. Here we provide additional evidence that exploratory activity is influenced by BDNF.

Personality in Captive Chimpanzees: Use of a Novel Rating Procedure

We present a new method to assess the personalities of captive chimpanzees (Pan troglodytes). Using individually generated bipolar constructs, experienced observers rated the personalities of chimpanzees on a five-point scale. Each observer chose a subset of his/her own constructs and we performed a separate factor analysis on each set of ratings. The analyses indicate four factors: dominance, sociability, machiavellianism, and anxiety. We propose that this factor structure will be useful in the development of a single rating instrument with which to assess the personalities of captive chimpanzees.

Errors and Response Latencies as a Function of Nodal Distance in 5-Member Equivalence Classes

Two experiments were conducted to investigate the relationship between nodal distance, response accuracy, and response latency during testing for emergent relations. In both experiments, undergraduate subjects first learned A-B, B-C, C-D, and D-E constituent relations of six 5-member equivalence classes. In Experiment 1, only selected tests of trained and of 0-, 1-, and 2-node tests of emergent relations were carried out in order to avoid testing of 0- or 1-node relations that might form constituents of the 2-node relations which were tested. In Experiment 2, all possible trained and derived relations were tested in random order. Although considerable individual variability was observed in both response times and accuracy for the 14 subjects completing Experiment 1, latencies for correct responses generally increased and response accuracy decreased as a function of nodal distance. There was no nodal distance effect for latencies of incorrect responses. In Experiment 2, these relationships between response times, response accuracy, and nodal distance were observed for 3-node relations in 5 out of 6 subjects. Analysis of error response latencies for 2 subjects who made sufficient errors revealed a nodal distance effect for 1 subject but not for the other. In both experiments, response times decreased as testing progressed, but response accuracy increased during testing only in the second experiment.

The Role of Individual Stimulus Names in the Emergence of Equivalence Relations: The Effects of Interpolated Paired-Associates Training of Discordant Associations between Names

After matching-to-sample (MTS) establishment of six A-B and six B-C trained relations between 18 visual stimuli, and prior to MTS testing for the emergence of A-B-C equivalence classes, undergraduate subjects in Experimental Group A-B were orally taught discordant paired associations (PA) between the names they had given to the A stimuli and their names for the B stimuli. Group A-C similarly learned associations between names for A and C stimuli conflicting with potential A-C transitivity relations based on MTS training. A control group learned associations between A names and neutral names. In subsequent MTS tests equivalence relations emerged with very few errors in the control group. In Group A-B PA links between the names of stimuli often displaced MTS-trained relations and symmetrical relations between the visual stimuli. In Group A-C PA links more often displaced MTS-based emergent transitivity and equivalence relations. Emergent relations formed from combinations of PA-based A-B associations and MTS-based B-C relations could displace purely MTS-based transitivity and equivalence relations in Group A-B, but similar hybrid relations did not emerge in Group A-C to displace MTS-based trained relations or their symmetrical inversions.These results provide evidence for an effective facultative role for the names of individual stimuli in equivalence class formation, but not for their obligate involvement.

The Role of Individual Stimulus Names in the Emergence of Equivalence Relations II: The Effects of Interfering Tasks Prior to and After Tests for Emergent Relations

In two experiments on equivalence class formation subjects were taught arbitrary trained relations between icons of familiar objects by matching-to-sample on a computer screen, before receiving four blocks of tests for trained and emergent relations. There were six AB/BC training sets so that potentially six ABC equivalence classes would be formed. In Experiment 1, an early discordant group of subjects was taught, prior to testing, oral paired associations between the names which the individual subjects gave to the A and the B visual stimuli in combinations which were systematically discordant with the AB matching-to-sample-based trained relations. In a second late discordant group, discordant paired associates were taught after two blocks of tests and in a third control group no discordant associations were taught. In the early discordant group it was found that paired associate-based links substituted for matching-to-sample-based links in many choices in all types of tests in which they could be implicated so that there was a significantly lower proportion than in the other two groups of choices consistent with equivalence class formation based upon the matching-to-sample training. It was found that for the late discordant group paired associate-based relations did not displace matching-to sample-based relations. A high proportion of choices continued to be consistent with equivalence classes based upon the preliminary matching-to-sample training, as was found in the control group. In a second experiment with interpolated paired associate-like training using the visual stimuli themselves (rather than their names) in a similar early versus late design it was found that choices based on discordant visual relations displaced a considerable proportion of choices based on matching to sample training, whether interpolated before or after some initial matching to sample testing. These results suggest that subjects’ names for individual stimuli may play a role in the formation of equivalence classes but play little part in the maintenance of such classes once formed.

Software multiple review

The Observer: software for behavioural research, version 2.0. Base Package for the IBM PC, PS/2 and compatible computers; Support Package for the TRS-80 Model 100, Tandy 102 and Olivetti M10 portable computers; Support Package for Psion Organiser hand-held computers; Support Package for the Epson PX-8 portable computer. Review of The Observer: a reply

Transitive Inference in Stimulus Equivalence and Serial Learning

The logical and behavioural properties of stimulus equivalence (SE) sets and serial learning (SL) sets are different, yet either can be derived from a randomly presented number of overlapping premise pairs, and both show transitive inference (TI). A within-participant experiment is reported which attempted to base both types of set on the same stimuli. To provide an ‘ecologically valid’ context the stimuli were photographs of 2 imaginary groups of 7 students ordered within each group by ‘exam grades’. Participants were given respondent-type training in ‘study phases’ in which the 12 premise pairs of photos were randomly presented without a response being required, alternating with ‘response phases’ in which the 10 participants in the ‘SE first’ group received matching-to-sample trials and the 10 in the ‘SL first’ group received trials with the study pairs of stimuli, in which they had to indicate whether these were in the same order as in the study phase or had been switched around. TI testing was then first conducted using the same requirement as in training, followed by similar tests using the other kind of response requirement. In a parallel sorting test participants were shown the 14 photos in random array on a screen and were asked to arrange them into 2 ordered groups. This sorting test was given 3 times, (1) after initial training on either SE or SL; (2) after TI testing with the same paradigm; (3) after TI testing with the opposite paradigm. Though the yield of accurate responding on the TI tests was poor, performance on initial TI testing was both more accurate and showed greater positive transfer to the other kind of TI test when SL preceded SE than vice versa. Results on the sorting task gave stronger indications of set formation than the TI tests, particularly in the SL first group. There were signs of the predicted increase in accuracy and decrease in RT as a function of increasing numbers of nodes in SL in the SL-first group, and some sign of the predicted inverse relation between accuracy and nodal number in SE for the SE-first group. When the groups switched to the opposite types of test to that on which they had been trained both showed an overall reduction in RTs and both showed decreasing RTs with increasing numbers of nodes. Unsurprisingly the experiment raised more questions than it could answer but suggested ways in which the similarities and differences between SL and SE, and how they interact, may be further explored.

OBSERVE: A multimedia course on the observational analysis of behavior

OBSERVE is a preliminary release of a multimedia course for teaching undergraduate and graduate students how and why to study behavior by direct observation. The instructional text and commentary and the self-test and examination materials are built around a series of exercises in which the student observes and categorizes film clips of the behavior of several different species in several different ways. Incorporation of elements from The Observer software for computer recording and video analysis implements fully computerized continuous recording. At present, the text, together with check sheets that the program generates, enables a comparison between one-zero, instantaneous, and continuous sampling of the same behavioral excerpts. Matrices are printed out for an exercise in calculating interobserver reliability. Another section supports carrying out and writing up a small observational project on human behavior in the field. Plans for the future development of OBSERVE are briefly described.

Strengths and Limitations of a Single- Comparison, Alternate-Response (SCAR) Procedure for Establishing Uni- and Multi- Nodal Stimulus Equivalence Classes

Factors determining the yield of establishing stimulus equivalence (SE) classes by means of a single-comparison, alternate-response (SCAR) procedure were explored in a series of experiments. Training involved Pavlovian study phases alternating with response phases until a criterion of performance was attained: there was no trial-by-trial feedback. Factors studied included the explicitness of instructions, types of stimuli used, number of classes to be established, number of nodes, types of tests, exemplar training, and response to an opportunity to relearn. Instructions did not need to be so explicit with 12 or fewer classes as they had been in an earlier study with 48 classes; stimulus type was not critical; but the procedure gave low yields with 3-nodal compared with 1-nodal classes, even with only 3 such classes. Added exemplar training helped to increase yield, but this was still poorer than in an otherwise similar study in which a matching-to-sample (MTS) procedure was substituted for the alternate response requirement. A key distinction may lie in the ambiguity of the alternate response requirement in contrast with the implicit rule in MTS that one of the stimuli present in the comparison array must be correct.