Non-verbal communication in severe aphasia: influence of aphasia, apraxia, or semantic processing?

Patients suffering from severe aphasia have to rely on non-verbal means of communication to convey a message. However, to date it is not clear which patients are able to do so. Clinical experience indicates that some patients use non-verbal communication strategies like gesturing very efficiently whereas others fail to transmit semantic content by non-verbal means. Concerns have been expressed that limb apraxia would affect the production of communicative gestures. Research investigating if and how apraxia influences the production of communicative gestures, led to contradictory outcomes. The purpose of this study was to investigate the impact of limb apraxia on spontaneous gesturing. Further, linguistic and non-verbal semantic processing abilities were explored as potential factors that might influence non-verbal expression in aphasic patients. Twenty-four aphasic patients with highly limited verbal output were asked to retell short video-clips. The narrations were videotaped. Gestural communication was analyzed in two ways. In the first part of the study, we used a form-based approach. Physiological and kinetic aspects of hand movements were transcribed with a notation system for sign languages. We determined the formal diversity of the hand gestures as an indicator of potential richness of the transmitted information. In the second part of the study, comprehensibility of the patients' gestural communication was evaluated by naive raters. The raters were familiarized with the model video-clips and shown the recordings of the patients' retelling without sound. They were asked to indicate, for each narration, which story was being told and which aspects of the stories they recognized. The results indicate that non-verbal faculties are the most important prerequisites for the production of hand gestures. Whereas results on standardized aphasia testing did not correlate with any gestural indices, non-verbal semantic processing abilities predicted the formal diversity of hand gestures while apraxia predicted the comprehensibility of gesturing.