SINUSOIDAL FOREARM TRACKING WITH DELAYED VISUAL FEEDBACK I - DEPENDENCE OF THE TRACKING ERROR ON THE RELATIVE DELAY

During forearm tracking of a sinusoidally moving target matching of pr oprioceptive and visual feedback was altered by introducing different visual delays. In five normal subjects seven target frequencies were t ested ranging from 0.3 to 1.5 Hz. For each target frequency nine diffe rent delays were used ranging from 0 to 120% of the cycle duration wit h target frequency and delay being varied randomly. Tracking error rev ealed a cyclic behaviour with an increase up to delays of about 50% of the target cycle duration and an improvement for delays larger than 5 0%. Modulation of response frequency was less pronounced compared with tracking error variation but also was dependent on relative phase. Th e response frequency matched the target frequency at delays of 0 and 1 00% of cycle duration and was slightly lower than the target frequency with relative delays of about 50%. The introduction of a visual delay during sinusoidal forearm tracking leads to a spatial in addition to the temporal mismatch between proprioception and vision. The temporal and the spatial incompatibility influence the tracking performance dif ferentially.