INFLUENCE OF AUDITORY PRECUING ON AUTOMATIC POSTURAL RESPONSES

An experiment was conducted to determine the influence of auditory pre cuing on posture control. Specifically, the influence of a warning sig nal on the onset latencies of the gastrocnemius (G) and tibialis anter ior (TA) muscles was determined. An audible 50-ms tone was presented t o subjects standing on a moveable platform and preceded a perturbation to standing balance by 500 ms. The perturbations were produced by an anterior or posterior translation (3 cm at 30 cm/s) of the support sur face. Unilateral electromyographic activity was recorded from G and TA muscles. In the first series of trials (series A), the muscle onset l atencies following perturbations with a nondirectionally specific prec ue, an invalid precue, and no precue were compared. In the second seri es of trials (series B), muscle onset latencies following perturbation s with a directionally specific precue, invalid precue, and no precue perturbations were compared. In series A, mean muscle onset latencies decreased following nondirectionally specific precues during forward a nd backward platform perturbations; respectively, TA 6% (91 +/- 9 ms t o 86 +/- 9 ms) and G 7% (93 +/- 6 ms to 87 +/- 5 ms). During series B, the TA and G muscle onset latencies decreased following directionally specific precues by 10.4% (92 +/- 12 ms to 82 +/- 6 ms) and 9.8% (92 +/- 9 ms to 83 +/- 6 ms), respectively. There were no significant diff erences between the types of precues. Thus, prior knowledge of a forth coming balance perturbation reduces postural muscle onset latency time s. In addition, specific prior knowledge reduces muscle onset latency time in the same manner as does nonspecific prior knowledge.