The idea that hand gestures and speech are connected is quite old. Some of these theories even suggest that language is primarily based on a manual communication system. In this thesis, I present four studies in which we studied the connections between articulatory gestures and manual grasps. The work is based on an earlier finding showing systematic connections between specific articulatory gestures and grasp types. For example, uttering a syllable such as [kɑ] can facilitate power grip responses, whereas uttering a syllable such as [ti] can facilitate precision grip responses. I will refer to this phenomenon as the articulation-grip congruency effect. Similarly, to the original work, we used special power and precision grip devices that the participants held in their hand to perform responses. In Study I, we measured response times and accuracy of grip responses and vocalisations to investigate whether the effect can be also observed in vocal responses, and to which extent the effect operates in the action selection processes. In Study II, grip response times were measured to investigate whether the effect persists when the syllables are only heard or read silently. Study III investigated the influence of grasp planning and/or execution on categorizing perceived syllables. In Study IV, we measured electrical activity in the brain during listening of syllables that were either congruent or incongruent with the precision or power grip, and we investigated how performing different grips affected the auditory processing of the heard syllables. The results of Study I showed that besides manual facilitation, the effect is observed also in vocal responses, both when a simultaneous grip is executed and when it is only prepared, meaning that overt execution is not needed for the effect. This suggests that the effect operates in action planning. In addition, the effect was also observed when the participants knew beforehand which response they should execute, suggesting that the effect is not based on the action selection processes. Study II showed that the effect was also observed when the syllables were heard or read silently, supporting the view that articulatory simulation of a perceived syllable can activate the motor program of the grasp which is congruent with the syllable. Study III revealed that grip preparation can influence categorization of perceived syllables. The participants were biased to categorize noise-masked syllables as being [ke] rather than [te] when they were prepared to execute the power grip, and vice versa when they were prepared to execute the precision grip. Finally, Study IV showed that grip performance also modulates early auditory processing of heard syllables. These results support the view that articulatory and hand motor representations form a partly shared network, where activity from one domain can induce activity in the other. This is in line with earlier studies that have shown more general linkage between mouth and manual processes and expands this notion of hand-mouth interaction by showing that these connections can also operate between very specific hand and articulatory gestures.
|Status||Publicerad - 2020|
|MoE-publikationstyp||G5 Doktorsavhandling (artikel)|
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- 515 Psykologi