An experimental investigation of the automatic/voluntary dissociation in limb apraxia

The ability of apraxic patients to perform gestures in everyday life is a controversial issue. In this paper, we aimed to evaluate the automatic/voluntary dissociation (AVD) in four patients affected by clinically relevant limb apraxia. For this purpose, we sampled different kinds of gestures belonging to patients' motor repertoire and then assessed their production in a testing session. Our experimental procedure consisted of two steps: in the first phase, we recorded gestures produced by patients in two natural conditions; in the second phase, we assessed production of correctly produced tool-actions, and of spontaneous non tool-actions and meaningless conversational (cohesive and beats) gestures under different modalities. AVD was observed for all types of gestures, albeit to different degree in single patients. The present findings demonstrate that the context provides strong bottom-up cues for the retrieval of motor patterns, while artificial testing conditions impose an additional cognitive load.     

The seeds of spatial grammar in the manual modality

Sign languages modulate the production of signs in space and use this spatial modulation to refer back to entities—to maintain coreference. We ask here whether spatial modulation is so fundamental to language in the manual modality that it will be invented by individuals asked to create gestures on the spot. English speakers were asked to describe vignettes under 2 conditions: using gesture without speech, and using speech with spontaneous gestures. When using gesture alone, adults placed gestures for particular entities in non-neutral locations and then used those locations to refer back to the entities. When using gesture plus speech, adults also produced gestures in non-neutral locations but used the locations coreferentially far less often. When gesture is forced to take on the full burden of communication, it exploits space for coreference. Coreference thus appears to be a resilient property of language, likely to emerge in communication systems no matter how simple.