Voice recognition in aphasic and non-aphasic stroke patients

Whereas denotative recognition of meaning via spoken language is undoubtedly a function of the dominant hemisphere, there are hints as to the superiority of the non-dominant hemisphere in detecting the author of a language message, at least if it is written (Heckmann et al. 2001). This study was undertaken to show if similar notions hold true for oral language. 20 patients (5 female, 15 male) with left (LH; N=11, mean age 66.3±7.7 years) or right (RH; N=9, mean age 64.1±11.1 years) hemisphere ischemic strokes (mean time post-onset 2.4±2.8 months) were compared on a task which required them to identify one familiar person (partner) out of six by listening to recordings of vowels, consonant-vowel combinations, words, and sentences. All LH patients were aphasic, all RH were not. The lesions were distributed symmetrically. All patients were right-handed and spoke German as their mother language. Patients with bilateral lesions, multiple infarcts, dementia, apparent attentional problems, depression or amnesia were not included. In addition, 17 healthy controls (HC) were assessed (mean age 64.1±5.2 years).

The two stroke patient groups did not differ with respect to age, sex, memory (Wechsler Memory Scale – Revised) or depression (Hamilton Depression Scale). RH patients, however, obtained worse results on a concentration test for elderly people than both, LH and HC. The mean of the combined auditory person recognition for LH and RH was only marginally inferior to HC (76% vs. 74%). Remarkably, RH patients differed from both, LH and HC on voice recognition P<0.05), be it for immediate recognition alone or in combination with delayed recognition. Only the percentage of delayed recognitions was equal. The differences were most marked on a word level.

These results underscore the dominance of the right (non-dominant) hemisphere in discovering the author of a spoken message (individual or “phonognomic“ recognition). LH, although aphasic and impaired with understanding the oral message, were superior in this respect, while RH patients either did not recognize the familiar speaker or it took them longer to identify him or her.

Literature: Heckmann JG, Lang CJG, Neundörfer B. Recognition of familiar handwriting in stroke and dementia. Neurology 2001;57:2128–2131