SIMPLE REACTION-TIME RESPONSES TO MECHANICAL AND ELECTRICAL STIMULI IN HUMAN MASSETER MUSCLE

The latencies of the simple reaction-time responses for opening and cl osing of the jaws in response to taps and pushes on teeth and lip shoc ks were measured in human adults. The reaction times were scored from both the integrated electromyographic (EMG) signal in individual trial s, and from the cumulative sum (CUSUM) of the averaged EMG response to 50 stimuli. The mean reaction times for both closing and opening were about 80-90 ms for taps and electrical lip shocks, and about 140 ms f or push, measured from the CUSUMs. The reaction times in individual tr ials were difficult to measure from the EMG signal because of the unst eady baseline. In contrast, the reaction times measured from the CUSUM s were clearly defined by the point at which the record began to move sharply above or below the baseline. However, because of the delays in herent in the CUSUM procedure, they were systematically longer than th e means of the trial-by-trial measurements.