Adaptation to display rotation and display gain distortions during drawing.

The relationship between movement extent and movement direction coding mechanisms was investigated using a visuomotor adaptation paradigm. To determine if these mechanisms are either modular or interdependent, young healthy college students were tested while they performed a visually guided drawing task that incorporated varying combinations of movement distance and direction distortions. Analysis of participants' standardized movement duration, initial directional error, and movement length over the course of the adaptation process revealed a certain degree of interdependence between direction and extent coding mechanisms. Specifically, changes in final adaptation levels and after-effects depended on the order of introduction of the visual distortions. This interaction can be characterized as unidirectional, where alterations in rotational feedback interfere with subsequent adaptation to gain changes, whereas alterations in "display gain" do not significantly impede the adaptation to "display rotation". Moreover, simultaneous exposure to gain and rotational distortions resulted in better learning. The results argue against an independent coding of movement direction and extent during adaptation by the central nervous system.