Abstract
In the present study, two different regimes of reciprocal graphic aiming movements, a cyclic and a discrete one, were contrasted to find an explanation for the earlier found advantage, in terms of rate of information transmission, of cyclic versus discrete aiming (Smits-Engelsman, Van Galen & Duysens, submitted). In the cyclic condition, reciprocal aiming movements consisted of back-and-forth movements made by the wrist that were performed in immediate succession for 20 seconds. In the discrete condition the same trajectories were drawn as 20 single strokes, starting after a go signal and stopping each time after reaching the target area. The targets had two levels of spatial accuracy, which was kept constant during a task. Moreover, the amplitude of the back and forth movement was either 2.5 or 5 cm. In the simple task condition these amplitudes were kept constant for a complete series of movements whereas in the complex condition these distances alternated between each consecutive back and forth movement pair. The results confirmed that the effective Index of Performance for cyclic movements is much higher than for discrete movements. However, if two amplitudes had to be executed alternately, part of the advantage of cyclic over discrete movement regime was lost, suggesting that one of the critical advantages of an oscillatory movement is the simplicity of the movement structure in which one moves around a virtual midpoint. It is argued that the remaining significant benefit of cyclic movement over discrete movements in the most complex aiming task is caused by soft tissue rebound. It is proposed that in cursive script this more efficient movement regime is better fulfilled than in print of capital letter writing.
