Rehabilitation of past tense verb production and non-canonical sentence production in left inferior frontal non-fluent aphasia

Abstract

Background: Studies devoted to improving past tense verb production in Broca's aphasic patients are sparse. Of the existing studies few have produced generalised improvement on untreated verbs, although one study has shown improvement on untreated regular, but not irregular, verbs (Weinrich, Boser, & McCall, 1999). Within a single mechanism account of past tense verb production (McClelland & Patterson, 2002a, 2002b), irregular verbs fall into clusters that share similar transformations from their stem to past tense. No studies to our knowledge have explored whether strengthening irregular verb representations during rehabilitation can support production on untreated irregulars from the same irregular clusters.

Aims: The aim of the current paper was to test the single mechanism claim that generalised improvement can be directed via irregular verb clusters in a Broca's aphasic participant (DS). We treated past tense verb production in sentences by using a mapping therapy, with the aim of maximising improved production of past tense verbs at both the single word and sentence level.

Methods & Procedures: The study used a thematic mapping procedure requiring DS first to describe what was happening in a picture with two characters twice, beginning with different characters each time. Two thematic questions followed and DS was asked to produce the canonical and non-canonical sentences again. Non-canonical sentences required past tense verb production. Pre- and post-treatment baselines were administered to test gains in sentence production, sentence comprehension, and verb production. Generalised verb production was assessed using three untreated sets: regular verbs, irregular verbs from the same “clusters” as treated items, and irregulars from other verb clusters.

Outcomes & Results: Generalised improvements were seen in the production of non-canonical sentences. Regular and irregular past tense verb production also improved, in both single word and sentence production modalities. There was significant generalised improvement to the untreated regular verb set. Interestingly, the improvement on treated irregular verbs generalised only to untreated irregulars from the same clusters as treated verbs.

Conclusions: The findings suggest that past tense verb production can be improved by promoting mapping between semantic and syntactic levels of sentence processing. The generalisation to untreated verbs with similar transformations from their stem to their past tense is promising from a clinical standpoint, suggesting that generalisation may be directed in this way. Our findings also demonstrate how rehabilitation studies can contribute to the current theoretical debate between competing models of past tense verb production. Here, the findings support an account positing generalisation across clusters of irregular verbs.

Keywords:

• Past tense verb
• Single mechanism
• Dual mechanism
• Aphasia
• rehabilitation

Acknowledgments

The author is now working as a Research Associate at: Department of Psychiatry, University of Cambridge, Cambridge, UK; The Oliver Zangwill Centre, Princess of Wales Hospital, Ely, Cambridgeshire, UK; and MRC Cognition and Brain Sciences Unit, Cambridge, UK.

This work was completed by the first author, LH, in partial fulfilment of a PhD at the University of Birmingham. Many thanks to the School of Psychology for funding the PhD project. We are extremely grateful to DS for his patience and constant enthusiasm throughout the testing sessions.

Notes

¹ Corrected FWE p = .01 Extent threshold including only significant blobs containing ≥ 100 voxels. NB: Grey matter lesion appears in red and white matter lesion in green. The lesion was created in SPM and added as an overlay onto a standard multi-slice template in MRIcron. The SPM analysis was a one sample t-test with the covariates healthy (140 brains aged 40+) vs participant, age, and gender.