Measurement of subvocal speech: correlations between two muscle leads and between two recording methods.

Electromyographical (EMG) activity was recorded from both the lip and the chin speech muscles of 46 preschool children while they silently memorized names of pictures in a memory task. Correlations between responses from the lip and chin muscle channels, performed for each trial, were high. A more sensitive measurement procedure of squaring and integrating voltages was used to quantify EMG activity. Correlations per each trial of squared, integrated voltages with amplitude of the single highest pen deflections (a commonly used measurement in studies of subvocal speech) were somewhat lower than desirable; correlations with amplitude of the five highest pen deflections were noticabley higher.