Auditory-verbal analysis in aphasia

ABSTRACT

Background: Comprehension deficits are more pervasive in aphasic syndromes than initially believed. They affect differentially distinct levels of auditory-verbal comprehension. Current evidence from functional imaging studies in healthy subjects indicates that distinct levels of auditory-verbal analysis involve specific networks.

Aims: The aim of this study is (1) to assess the different levels of auditory-verbal analysis with real-time monitoring tasks in patients with aphasia, (2) to compare the performance profiles across aphasia types, (3) to analyse patterns of dissociations vs. co-occurrence at specific levels, and (4) to establish correlations between disturbances at specific levels of auditory-verbal analysis and sites of lesions.

Methods & Procedures: Forty-two right-handed patients with aphasia associated with a first unilateral left-hemispheric lesion underwent tests monitoring (1) phonetic-phonological, (2) lexical, (3) morphosyntactic, (4) semantic-pragmatic (at sentence level), and (5) linguistic prosody processing. Anatomo-clinical correlations were established by means of voxel-based lesion-symptom mapping.

Outcomes & Results: Widespread deficits at multiple levels occurred across aphasic syndromes. In a given patient, more levels tended to be impaired in Wernicke’s and global aphasia than in Broca’s or conduction aphasia. Syllable and word processing double-dissociated behaviourally and partially anatomically. Morphosyntactic deficits were always accompanied by semantic-pragmatic deficits. Anatomo-clinical correlations implicated the dorsal auditory stream in syllable discrimination, the ventral stream in semantic processing at lexical level and in linguistic prosody and both streams in lexical frequency effect. Basal ganglia were implicated in syntactic and semantic processing at sentence level.

Conclusions: At prelexical and lexical levels, syllable and word processing appear to be independent of each other. At sentence level, parsing of syntactic structure appears to be necessary for successful semantic-pragmatic analysis. Thus, the fine-grained evaluation of auditory-verbal processing capacities and of the integrity of specialised processing networks in brain-damaged patients provides a sensitive diagnostic tool.

KEYWORDS:

• Monitoring tasks
• aphasia
• language
• auditory-verbal processing streams

Acknowledgements

We thank Prof. François Grosjean for the longstanding collaboration on the real-time monitoring of auditory-verbal comprehension battery; Dr. Rolf Frischknecht for the referral of patients; and Dr. Jean-François Knebel for expert advice on statistical analyses. We thank also all patients who participated in our study.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. By convention, in linguistics, a statement considered incorrect (agrammatical, apragmatic …) is preceded by an asterisk (*).

Additional information

Funding

This work was supported by the Swiss National Science Foundation under grant number 320030-124897 and 320030B-141177 to Stephanie Clarke.