As a part of my research into imitation, I have performed several psychophysical experiments to gain further insight into human perceptual and motor behavior in imitation. I have so far been involved in three psychophysical studies, briefly described below.
Our results conclusively found that for all types of stimuli we presented, the subjects tended to fixate on the hand, regardless of whether they were imitating or just watching. The results lend insight into the connection between visual perception and motor control, suggesting that: 1) people analyze human arm movements largely by tracking the hand or the end-point, even if the movement is performed with the entire arm, and 2) when imitating, people use internal innate and learned models of movement, possibly in the form of motor primitives, to recreate the details of whole-arm posture and movement from end-point trajectories. Details of this study are found in this downloadable paper.
The stimuli consisted of 20 video clips showing a sequence of human arm movements. We tested six different conditions, involving rehearsal and no-rehearsal (watching, or performing simultaneous imitation, respectively), immediate and delayed (imitation upon completion of video, or with some delay), and with or without mental distractors. Finally, we tested two consecutive imitations. We found that in all of the six conditions we tested, the subjects performed significantly better on the first imitation than on the second. However, this effect is mainly due to the two delayed conditions without simultaenous rehearsal, in which the first imitation is overwhelmingly better than the second, while in the remaining four conditions, it is only a marginally better or the same as the first. Given the rather straightforward nature of the movements used in the stimuli, we can conclude that subjects generated the motor imitation likely by resorting to generic movement patterns that were familiar, and did not improve those through repeated execution. This is consistent with our finding that even when the subjects were made to fixate away from the end-point, as they would naturally do, but instead look at the elbow, the quality of their subsequent imitation was not drastically affected. Additionally, this fits well within our model of imitation, which postulates that all observed human movements are mapped directly (through the mirror system) onto a combination of known motor programs or primitives, and it is the combination of those primitives, through rehearsal, that generates novel motor skills. The details of the results are described in a downloadable paper..