Abstract
It is well known that the kinematics of an action is modulated by the underlying motor intention. In turn, kinematics serves as a cue also during action observation, providing hints about the intention of the observed action. However, an open question is whether decoding others’ intentions on the basis of their kinematics depends solely on how much the kinematics varies across different actions, or rather it is also influenced by its similarity with the observer motor repertoire. The execution of reach-to-grasp and place actions, differing for target size and context, was recorded in terms of upper-limb kinematics in 21 volunteers and in an actor. Volunteers had later to observe the sole reach-to-grasp phase of the actor’s actions, and predict the underlying intention. The potential benefit of the kinematic actor-participant similarity for recognition accuracy was evaluated. In execution, both target size and context modulated specific kinematic parameters. More importantly, although participants performed above chance in intention recognition, the similarity of motor patterns positively correlated with recognition accuracy. Overall, these data indicate that kinematic similarity exerts a facilitative role in intention recognition, providing further support to the view of action intention recognition as a visuo-motor process grounded in motor resonance.
Highlights
When we observe another individual performing an action, several aspects concur to inform us about what action is taking place, and which motor intention is driving its performance
The study was approved by the local ethical committee (Comitato Etico Unico per la Provincia di Parma) and was conducted according to the principles expressed in the Declaration of Helsinki
These results showed that when the task afforded a social intention, the reaching was slower compared to the no-social context, regardless of the target size
Summary
When we observe another individual performing an action, several aspects concur to inform us about what action is taking place, and which motor intention is driving its performance. While the maximal finger aperture during reaching is the parameter most sensitive to the variation of intrinsic object properties, and especially its size, a variation of reach duration and deceleration timing emerged in response to tasks with different accuracy requirements (i.e., grasping an object to place it carefully as opposed to throwing it). This was in line with the “precision hypothesis” formulated by Marteniuk and colleagues[15] proposing that a higher level of precision and accuracy of the action would be associated to a longer deceleration phase of the movement. Since different intentions are represented by different kinematic patterns, if the expressed movement variation is higher, the resulting intention-discrimination task becomes easier
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