Internal Representation of Movement Sequences on Reproduction of Static Drawings and the Trajectories of Moving Objects

Abstract

We report here studies of the nature of neural codes (perceptual, abstract, or motor) used for the internal representation of elements of sequences of movements in the CNS. Results from two experiments are presented, in which two independent groups of subjects (16 right-handed adults in each) were tasked with using a graphics tablet to reproduce trajectories – unclosed broken trajectories consisting of straight-line segments and specified visually. Two types of visual trajectory presentation were used: static (drawings) and dynamic (a moving object). The results showed: 1) that over a range of delays from 0 to 1 sec, the latent period of delayed reproduction of the visually specified trajectory was greater when the sample was a moving object than when it was a static drawing, while with a delay of 3 sec, the latent periods were identical for the two trajectory presentation regimes; 2) that the latent period decreased exponentially with increases in the delay from 0 to 3 sec, the decay time constants differing for presentation of static (377 msec) and dynamic (656 msec) visual images. The data are consistent with the concepts that the internal representation of movement sequences is perceptual in nature and that transformation into motor codes occurs immediately before movement execution. The suggestion that the exponential contraction of the latent period of motor trajectory reproduction seen with increases in delay time may be linked with the process of transforming the initial sensory information on the whole visual scene into a perceptual representation of the trajectory is presented and evaluated.