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An fMRI study of emergent equivalence
relations. David W. Dickins, Krish D. Singh, Neil Roberts, Patrick Burns, John J. Downs, Phil Jimmieson and Richard P. Bentall University of Liverpool, MARIARC and University of Manchester, England 11 right-handed participants were functional magnetic resonance imaging (fMRI) scanned during testing for the emergence of equivalence relations based on prior matching-to-sample (MTS) training on 6 AB and 6 BC relations between iconic stimuli. Successive 5 min test runs for trained relations, symmetry, transitivity, and equivalence each contained ten 15 sec MTS ON epochs alternating with ten 15 sec OFF epochs. The OFF task involved all motor components of the ON task, but none of the stimulus relations. Afterwards a test of verbal fluency (VF) was given. All participants responded efficiently on the MTS tests of trained relations, and symmetry but there was a spread of speed and accuracy scores on tests involving transitivity. Comparison of brain activity in the ON and OFF conditions revealed wide bilateral increases, particularly in the frontal and parietal cortex, during all MTS tests. Similar frontal areas were implicated in VF except that the activity seen in Broca's area in VF was not found in MTS. Comparisons between participants based upon Statistical Parametric Mapping showed that the activity in the upper frontal cortex was more strongly left lateralised in those who did better in tests of transitivity than in those who did poorly. The implications of these initial findings will be cautiously discussed. Keywords: equivalence relations, stimulus classes, fMRI, verbal behaviour |
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