Action planning and congruency effect between articulation and grasping

Some theories concerning speech mechanisms assume that overlapping representations are involved in programming certain articulatory gestures and hand actions. In previous studies we have shown a compatibility effect between pronouncing or hearing meaningless syllables like [kɑ] and [ti] and simultaneously performing a power or a precision grip, respectively. The present study investigated whether action selection was necessary for the effect to manifest. The participants were visually presented with a cue for the upcoming manual response. After that, a written syllable "ka" or "ti" was presented at which point the cued grip was performed and the syllable pronounced. There was also a condition, where the grip was cued but only the vocal response was performed. Manual and vocal reaction times were relatively faster when the grip and syllable were compatible (e.g. power & [kɑ]) rather than incompatible (e.g. precision & [kɑ]). When no grip was performed (only cued), the effect was still apparent in vocal reaction times. These results suggest that preparation of a manual action is sufficient to influence vocalizations, and also that action selection is not, however, mandatory for this kind of syllable-grip correspondence.