Grasping the sound: auditory pitch influences size processing in motor planning

Growing evidence shows that individuals consistently match auditory pitch with visual size. For instance, high-pitched sounds are perceptually associated with smaller visual stimuli, whereas low-pitched sounds with larger ones. The present study explores whether this crossmodal correspondence, reported so far for perceptual processing, also modulates motor planning. To address this issue, we carried out a series of kinematic experiments to verify whether actions implying size processing are affected by auditory pitch. Experiment 1 showed that grasping movements toward small/large objects were initiated faster in response to high/low pitches, respectively, thus extending previous findings in the literature to more complex motor behavior. Importantly, auditory pitch influenced the relative scaling of the hand preshaping, with high pitches associated with smaller grip aperture compared with low pitches. Notably, no effect of auditory pitch was found in case of pointing movements (no grasp implied, Experiment 2), as well as when auditory pitch was irrelevant to the programming of the grip aperture, that is, in case of grasping an object of uniform size (Experiment 3). Finally, auditory pitch influenced also symbolic manual gestures expressing "small" and "large" concepts (Experiment 4). In sum, our results are novel in revealing the impact of auditory pitch on motor planning when size processing is required, and shed light on the role of auditory information in driving actions.