Influence of auditory precuing on automatic postural responses.

An experiment was conducted to determine the influence of auditory precuing on posture control. Specifically, the influence of a warning signal on the onset latencies of the gastrocnemius (G) and tibialis anterior (TA) muscles was determined. An audible 50-ms tone was presented to 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 surface. Unilateral electromyographic activity was recorded from G and TA muscles. In the first series of trials (series A), the muscle onset latencies following perturbations with a nondirectionally specific precue, an invalid precue, and no precue were compared. In the second series of trials (series B), muscle onset latencies following perturbations 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 and backward platform perturbations; respectively, TA 6% (91 +/- 9 ms to 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 differences between the types of precues. Thus, prior knowledge of a forthcoming balance perturbation reduces postural muscle onset latency times. In addition, specific prior knowledge reduces muscle onset latency time in the same manner as does nonspecific prior knowledge.