Background: Two main conflicting positions exist concerning the relationship of gesture and speech. The first claims that gesture and speech constitute a single bimodal production process that leads to an impairment of both communication channels in the case of aphasia. The second accounts for two independent but tightly coordinated processes with a trade-off relationship of gesture and speech. According to the latter assumption, speakers who have aphasia should be able to compensate for their verbal deficiencies through gesture. Studies provide evidence for both accounts. Furthermore, non-verbal capacities like semantic processing or manual praxis have been shown to influence the gestural performance of speakers who have aphasia. Aims: The first aim of the current study was to clarify the relationship between gesture and speech production in aphasia by exploring how much information speakers with aphasia conveyed by gesture versus speech in narrations. The second aim was to evaluate if these speakers make use of their full communicative potential through gesture. We compared gesture use in a verbal narration with gesture use in a silent condition, where participants were not allowed to speak. Furthermore, the influence of language and non-verbal cognitive capacities on gesture was examined. Methods & Procedures:Sixteen participants with varying degrees of aphasia severity retold short video clips in a verbal and a silent condition. In the latter, participants were asked to retell the stories by exclusively using gestures. Subsequently, healthy speakers judged the comprehensibility of gestures and of the spoken expression in the verbal narration in a forced-choice recognition task. Comprehensibility scores were compared between conditions and influencing linguistic and non-verbal factors were evaluated. Outcomes & Results: In the verbal condition, two participants conveyed more information through gesture than through spoken expression. Furthermore, half of the participants could augment gestural comprehensibility in the silent condition. Communicative efficiency of gesture was predicted by the pantomime-to-command test.
For over a century, pantomime of tool use has been employed to diagnose limb apraxia, a disorder of motor cognition primarily induced by left brain damage. While research consistently implicates damage to a left fronto-temporo-parietal network in limb apraxia, findings are inconsistent regarding the impact of damage to anterior versus posterior nodes within this network on pantomime. Complicating matters is the fact that tool use pantomime can be affected and evaluated at multiple levels. For instance, the production of tool use gestures requires the consideration of semantic characteristics (e.g. how to communicate the action intention) as well as motor features (e.g. forming grip and movement). Together, these factors may contribute substantially to apparent discrepancies in previously reported findings regarding neural correlates of tool use pantomime.In the current study, 67 stroke patients with unilateral left-brain damage performed a classic pantomime task. In order to analyze different error characteristics, we evaluated the proper use of grip and movement for each pantomime. For certain objects, healthy subjects may use body parts as representative for the object, e.g. use of the fingers to indicate scissors blades. To specify the pathological use of body parts as the object (BPO) we only assessed pantomime items that were not prone to this response in healthy participants. We performed modern voxel-based lesion analyses on MRI or CT data to determine associations between brain injury and the frequency of the specific types of pantomime errors.Our results support a model in which anterior and posterior nodes of the left fronto-temporo-parietal network contribute differentially to pantomime of tool use. More precisely, damage in the inferior frontal cortex reaching to the temporal pole is associated with an increased frequency of BPO errors, whereas damage to the inferior parietal lobe is predominantly linked to an increased frequency of movement and/or grip errors. Our work suggests that the validity of attempts to specify the neural correlates of limb apraxia based on tool use pantomime depends on differentiating the specific types of errors committed. We conclude that successful tool use pantomime involves dissociable functions with communicative aspects represented in more anterior (rather ventral) regions and motor-cognitive aspects in more posterior (rather dorsal) nodes of a left fronto-temporo-parietal network.
It was concluded that all 3 gesture types under investigation contributed to the expression of semantic meaning communicated by PWA. Gestures are an important communicative means for PWA and should be regarded as such by their interlocutors. Gestures have been shown to enhance listeners' interpretation of PWA's overall communication.
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