Humphries, Stacey and Holler, Judith and Crawford, Trevor Jeremy and Herrera, Elena and Poliakoff, Ellen (2016) A third-person perspective on co-speech action gestures in Parkinson's disease. Cortex, 78. pp. 44-54. ISSN 0010-9452
CORTEX_SH_accepted_Humphries_Feb_2016_.pdf - Accepted Version
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Abstract
A combination of impaired motor and cognitive function in Parkinson’s disease (PD) can impact on language and communication, with patients exhibiting a particular difficulty processing action verbs. Co-speech gestures embody a link between action and language and contribute significantly to communication in healthy people. Here, we investigated how co-speech gestures depicting actions are affected in PD, in particular with respect to the visual perspective—or the viewpoint – they depict. Gestures are closely related to mental imagery and motor simulations, but people with PD may be impaired in the way they simulate actions from a first-person perspective and may compensate for this by relying more on third-person visual features. We analysed the action-depicting gestures produced by mild-moderate PD patients and age-matched controls on an action description task and examined the relationship between gesture-viewpoint, action-naming, and performance on an action observation task (weight judgement). Healthy controls produced the majority of their action-gestures from a first person perspective, whereas PD patients produced a greater proportion of gestures produced from a third person perspective. We propose that this reflects a compensatory reliance on third-person visual features in the simulation of actions in PD. Performance was also impaired in action-naming and weight judgement, although this was unrelated to gesture viewpoint. Our findings provide a more comprehensive understanding of how action-language impairments in PD impact on action communication, on the cognitive underpinnings of this impairment, as well as elucidating the role of action simulation in gesture production.