Do gestures have a hand in verb retrieval? Investigation of iconic and non-iconic gestures in aphasia

Abstract

Background: According to the lexical retrieval hypothesis (LRH), the primary function of gestures is to facilitate word retrieval. Thus, individuals with aphasia (IWA) might benefit from gestures in case of word retrieval impairments. However, the facilitative effect of gestures on word finding is still unclear since most facilitation/ treatment studies combined gesture with linguistic cues. The LRH claims that the semantic content of a gesture is decisive for a facilitation effect on word retrieval. However, it remains unclear if and how IWA can perform adequate iconic gestures, especially in the presence of hemiparesis or limb apraxia. Thus, in the present study, we systematically studied the effect of iconic and non-iconic gesture production on oral verb naming in IWA and analysed the iconicity of gestures produced by IWA and healthy controls. Aims: In the present study, we aimed (1) to investigate the potential facilitation effect of iconic and non-iconic gestures on verb retrieval in IWA and (2) to examine the IWA's ability to produce adequate iconic gestures. Methods & Procedures: Six IWA with impairments in naming verbs arising from a phonological, a lexical-semantic, or a combined deficit participated in a multiple single-case study targeting oral verb production. In the first experiment, IWA were asked to name pictures and to simultaneously perform either a relevant iconic gesture, a non-iconic gesture, or no gesture at all. In the second experiment, the videorecorded gestures produced during verb naming in the iconic gesture condition were rated for iconicity and compared to the iconicity of iconic gestures produced by 12 language-unimpaired controls. Results: The accuracy in oral naming of verbs (Experiment 1) did not differ significantly between all conditions. Most IWA (n = 5) were able to produce iconic gestures, irrespective of hemiparesis or limb apraxia, since the iconicity ratings did not differ significantly from language-unimpaired controls (Experiment 2). Conclusions: In contrast to the general assumption of the LRH, no gesture facilitation effect was observed in the verb naming performance of IWA. Moreover, the majority of the IWA could perform iconic gestures in a similar way as language-unimpaired participants despite the presence of a hemiparesis or limb apraxia. Hence, the absence of a facilitation effect in the iconic gesture condition seems not to originate from an inability to produce adequate iconic gestures. Further research with more IWA is required in order to replicate our results.