Reaching and grasping with the tongue: Shared motor planning between hand actions and articulatory gestures.

Research has shown connections between articulatory mouth actions and manual actions. This study investigates whether forward-backward hand movements could be associated with vowel production processes that programme tongue fronting/backing, lip rounding/spreading (Experiment 1), and/or consonant production processes that programme tongue tip and tongue dorsum actions (Experiment 2). The participants had to perform either forward or backward hand movement and simultaneously pronounce different vowels or consonants. The results revealed a response benefit, measured in vocal and manual reaction times, when the responses consisted of front vowels and forward hand movements. Conversely, back vowels were associated with backward hand movements. Articulation of rounded versus unrounded vowels or coronal versus dorsal consonants did not produce the effect. In contrast, when the manual responses of forward-backward hand movements were replaced by precision and power grip responses, the coronal consonants [t] and [r] were associated with the precision grip, whereas the dorsal consonant [k] was associated with the power grip. We propose that the movements of the tongue body, operating mainly for vowel production, share the directional action planning processes with the hand movements. Conversely, the tongue articulators related to tongue tip and dorsum movements, operating mainly for consonant production, share the action planning processes with the precision and power grip, respectively.

Systematic Influence of Perceived Grasp Shape on Speech Production.

Previous research has shown that precision and power grip performance is consistently influenced by simultaneous articulation. For example, power grip responses are performed relatively fast with the open-back vowel [a], whereas precision grip responses are performed relatively fast with the close-front vowel [i]. In the present study, the participants were presented with a picture of a hand shaped to the precision or power grip. They were required to pronounce speech sounds according to the front/above perspective of the hand. The results showed that not only the grip performance is affected by simultaneously pronouncing the speech sound but also the production of speech sound can be affected by viewing an image of a grip. The precision grip stimulus triggered relatively rapid production of the front-close vowel [i]. In contrast, the effect related to the power grip stimulus was mostly linked to the vertical dimension of the pronounced vowel since this stimulus triggered relatively rapid production of the back-open vowel [a] and back-mid-open vowel [o] while production of the back-close vowel [u] was not influenced by it. The fact that production of the dorsal consonant [k] or coronal consonant [t] were not influenced by these stimuli suggests that the effect was not associated with a relative front-back tongue shape of the articulation in the absence of changes in any vertical articulatory components. These findings provide evidence for an intimate interaction between certain articulatory gestures and grip types, suggesting that an overlapping visuomotor network operates for planning articulatory gestures and grasp actions.