Kinesthetic reaction times in the speech motor system

Abstract

Several speech production theorists have cited long‐latency RT (reaction times) in the speech musculature as a partial basis for discounting the potential role of afferent feedback. However, these RT latencies, ranging from 120 to 140 ms, have been obtained primarily with auditory and visual stimuli. In the present experiment we were interested in determining the mininal response latency capabilities of the speech control system under optimal learning and stimulus conditions. Subjects were instructed to produce labial closure following a brisk mechanical stretch stimulus applied to the oral angle. In most subjects, the voluntary orbicularis oris (OOI) response consisted of: (I) a marked reduction of “resting” EMG activity, followed in 10–15 ms by, (2) the interference pattern related to activation of OOI. In highly trained subjects, RT latencies from the onset of the stimulus to the onset of OOI activation were frequently as short as 50 ms with a large percentage less than 75 ms. Latencies to the onset of the EMG reduction were correspondingly shorter. These findings will be discussed in relation to (I) comparable “kinesthetic” RT results recently reported in the spinal motor system, and (2) implications for the role of afferent mechanisms for speech motor control. [Work supported by NSF grant 13274.]