Abstract
Perception of the final position of a moving object or creature is distorted forward along its actual or implied motion path, thus enabling anticipation of its forthcoming position. In a previous research, we demonstrated that viewing static snapshots that imply body actions activates the human motor system. What remains unknown, however, is whether extrapolation of dynamic information and motor activation are higher for upcoming than past action phases. By using single-pulse transcranial magnetic stimulation, we found that observation of start and middle phases of grasp and flick actions engendered a significantly higher motor facilitation than observing their final postures. Differential motor facilitation during start and end postures was independent of finger configuration at the different hand apertures. Subjective ratings showed that modulation of motor facilitation was not due to the amount of implied motion per se but to the forward direction of the motion path toward upcoming phases. Thus, motor facilitation proved maximal for the snapshots evoking ongoing but incomplete actions. The results provide compelling evidence that the frontal component of the observation-execution matching system is preferentially activated by the anticipatory simulation of future action phases and thus plays an important role in the predictive coding of others' motor behaviors.
Highlights
The full sequence of motion is rarely visible during interactions with a dynamic world
Because we aimed to evaluate the differential modulation of Motor-evoked potentials (MEPs) recorded from the first dorsal interosseous (FDI) muscle during observation of the different phases of actions, optimal scalp position (OSP) and resting motor threshold (rMT) were determined for the FDI
To test whether mirror motor facilitation is higher during extrapolation of dynamic information about the upcoming action phases than the past ones, we compared normalized MEP amplitudes during observation of static snapshots depicting the start, middle, and end postures of grasp and flick actions (Fig. 2)
Summary
The full sequence of motion is rarely visible during interactions with a dynamic world. Even when there is no obstacle to our view, the intrinsic delay of our perceptual processing and our motor responses requires an anticipatory representation of the motion sequence in order to interact optimally with moving objects or creatures (SchutzBosbach and Prinz 2007; Perrett et al 2009). This top-down modulation of visual perception may use previous experiences and knowledge on motion to predict and anticipate the forthcoming position of moving entities and create a representation of events occurring in the near future (Ingvar 1985). Neurons in the monkey’s superior temporal cortex respond to the presentation of both moving body parts and static images of body postures implying preceding action (Jellema and Perrett 2003a, 2003b; Puce and Perrett 2003; Barraclough et al 2006; Perrett et al 2009)
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