[Internal representation of movement sequences built upon either static line drawings or trajectories of moving...

In this paper, we explore the issue of the nature (perceptual, abstract, or motor) of neural codes used by CNS in order to store the internal representation of elements of a sequence of movements. Reported are the results of two experiments in which two independent groups of 16 right handed adults repeated, after a given delay, the piecewise trajectories (open polygonal chains) using the graphical tablet. A trajectory was shown either as a static line-drawing (static mode) or a small moving pointer (dynamic mode). The results show that: 1) for the delay varying from 0 to 1 s, the latent time of the trajectory production is greater in the dynamic than in the static mode, with the latent time is no different under to presentation conditions when the production delay reaches 3 s; 2) the latent time is exponentially decaying as the trajectory production delay increases from 0 to 3000 ms, with the characteristic decay time being different in the static (377 ms) and the dynamic (656 ms) presentation modes. The results of the present study are in line with the view that the internal representation of the sequence of movements is perceptual and it is converted into the motor codes at the later stages prior to movement execution. It is suggested in the paper that the observed exponential decay of the latent time might be related to the transformation of the early sensory (iconic) representation into the perceptual trajectory representation.