Pandas and Penguins, Monkeys and Caterpillars: Problems of Cluster Analysis in Semantic Verbal Fluency

Cathodal tDCS of the bilateral anterior temporal lobes facilitates semantically-driven verbal fluency

In a verbal fluency task, a person is required to produce as many exemplars of a given category (e.g., 'animals', or words starting with 'f') as possible within a fixed duration. Successful verbal fluency performance relies both on the depth of search within semantic/phonological neighborhoods ('clustering') and the ability to flexibly disengage between exhausted clusters ('switching'). Convergent evidence from functional imaging and neuropsychology suggests that cluster-switch behaviors engage dissociable brain regions. Switching has been linked to a frontoparietal network dedicated to executive functioning and controlled lexical retrieval, whereas clustering is more commonly associated with temporal lobe regions dedicated to semantic and phonological processing. Here we attempted to modulate cluster-switch dynamics among neurotypical adults (N = 24) using transcranial direct current stimulation (tDCS) delivered at three sites: a) anterior temporal cortex; b) frontal cortex; and c) temporoparietal cortex. Participants completed letter-guided and semantic category verbal fluency tasks pre/post stimulation. Cathodal stimulation of anterior temporal cortex facilitated the total number of words generated and the number of words generated within clusters during semantic category verbal fluency. These neuromodulatory effects were specific to stimulation of the one anatomical site. Our findings highlight the role of the anterior temporal lobes in representing semantic category structure and support the claim that clustering and switching behaviors have distinct substrates. We discuss implications both for theory and application to neurorehabilitation.

Capturing additional information about the organization of entries in the lexicon from verbal fluency productions

Troyer and colleagues [Troyer, A. K., Moscovitch, M., & Winocur, G. (1997). Clustering and switching as two components of verbal fluency: evidence from younger and older healthy adults. Neuropsychology, 11(1), 138-146] developed a seminal method to measure clustering and switching behaviors during verbal fluency (VF) productions. We sought to expand the reach of their system by modifying the scoring rules. Compared to the Troyer system, our modifications yield comparable estimates of interrater reliability and similar patterns of correlation with demographic characteristics for both clustering and switching in healthy adults. However, two objective measures of word relatedness (interword interval timing and latent semantic analysis) confirm that our revisions capture additional information about the organization of entries in the lexical network.

A discursive psychology critique of semantic verbal fluency assessment and its interpretation

Semantic verbal fluency (SVF), a psychological assessment method used in experimental research and clinical practice, requires participants to produce as many words as possible from a given superordinate category (e.g., “animals,” “vehicles”). Features of responses, such as the prototypicality and ordering of items, are then interpreted as if revealing details about the organisation—or, in instances of ostensibly atypical performance, disorganisation—of participants’ underlying conceptual and/or semantic systems. In this paper, we draw upon perspectives from Discursive Psychology, particularly the work of Derek Edwards (e.g., Edwards, 1997), to argue against this position. Following critical discussion of SVF’s strongly cognitivist theoretical foundations, we present analyses of social interactions across various contexts, including the real-life administration of the paradigm with a child with autism, to suggest that performance is unavoidably socially mediated rather than solely internally driven. Our arguments challenge SVF’s validity and its role in the description of “cognitive disorder.”