Jaw, head and finger tracking behaviour with delayed visual feedback

The contribution of visual feedback to visuomotor tracking of jaw, head and finger was established by delaying the visual feedback display. Fourteen subjects (seven females, seven males; 20-30 years of age) used a movable metal bar to track a pseudorandom waveform on an oscilloscope screen. The tracking signals were recorded by means of a linear variable displacement transducer, amplified and digitized. Two approaches were applied for data analysis: (1) a cross-correlation analysis; (2) a power spectral analysis. On delaying the visual display, response delays for finger tracking increased significantly. A significant spectral shift occurred when a delayed feedback display (0.5-1.0 s) was introduced in both head and finger tracking experiments. A spectral change also occurred after inducing finger fatigue. On the other hand, neither the response delays nor the median frequencies of jaw tracking signals were significantly affected by modifications in the visual feedback display or by maximal voluntary clenching. Another interesting finding was the increase of the median frequency after periodontal anaesthesia. It was concluded that visual information is predominantly involved in finger and head tracking. Interactions between the visual system and the jaw motor system seem unlikely. Jaw tracking control probably relies on well-developed proprioceptive and exteroceptive inputs.