Kinematic analysis of lip and voice spectrum analysis were used to assess the influence of both execution and observation of arm-mouth-related actions on speech production. In experiments 1 and 2 participants brought either a cherry or an apple to their mouth and either pronounced the syllable BA (experiment 1) or emitted a nonspeech-related vocalization (experiment 2). In the other three experiments participants observed arm actions performed by the experimenter and pronounced the syllable BA. In experiment 3, they observed the action of bringing the cherry or apple to the mouth. In experiments 4 and 5, they observed a pantomime of the same action performed by the experimenter with his own arm (experiment 4) or with a nonbiological arm (experiment 5). The results showed that the formant 2 of the vowel 'a' increased when participants executed the bringing-to-the-mouth act with the apple or observed its execution or pantomime with the experimenter's arm (experiments 1, 3 and 4). In contrast, no modification in the vowel formants was found during a nonspeech-related vocalization (experiment 2) and during observation of an action with a nonbiological arm (experiment 5). Finally, the opening of the lips was larger when the participant brought the apple rather than the cherry to the mouth and pronounced BA (experiment 1). Taken together, the results of the present study suggest that the execution and observation of the bringing-to-the-mouth action activate a mouth articulation posture (probably due to the act of food manipulation with the mouth) which selectively influences speech production. They support the idea that the system involved in speech production shares and may derive from the neural substrate which is involved in the control of arm-mouth interactions and, in general, of arm actions.
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