Recognition of thematic and taxonomic conceptual relations in patients with aphasia

Background: There is mounting evidence that there exist conceptual non-verbal deficits in patients with aphasia. In the current paper, taxonomic and thematic conceptual relations are the focus of interest. There is a debate surrounding this topic regarding whether they are part of the same semantic system or there are independent systems dedicated to each kind of relations. Aims: Our aim was to study and look for possible dissociations in a group of fluent and non-fluent aphasic patients on their ability to recognise conceptual relations (taxonomic and thematic). Methods & Procedures: Previous studies have usually proposed forced-choice tasks, which give the patients closed response options and do not allow the researcher to assess the criteria for the choice the participants have made. In the following study we assigned different types of conceptual tasks (forced choice and free choice) to a group of 25 stroke patients (7 fluent and 18 non-fluent aphasic patients), as well as 30 healthy control participants. We assessed the hit rates and the response criteria followed by the patients. Outcomes & Results: The results showed that although all aphasic patients experienced difficulties in establishing both types of conceptual relations in verbal tasks, dissociations were observed particularly in non-verbal tasks showing poor performance in thematic relations. This was especially noticeable in non-fluent aphasic patients. Meanwhile, fluent aphasic patients showed more difficulty in establishing taxonomic relations in the pictorial free-choice task and a tendency to use thematic criteria. Conclusion: These results support the claim that there exist separate systems for both kinds of conceptual relations. Implications for the assessment of semantic deficits in aphasic patients were discussed. © 2015 Taylor & Francis.