Comparison of electromyographic signals from different electrode placements in the palatoglossus muscle.

It is a general practice to insert a single electrode pair per muscle for electromyographic recording. The location of electrode insertion influences the character of the signal obtained. The objective of the experiment was to study the relationships between electromyographic signals recorded simultaneously from different locations in an anatomically simple muscle involved in speech production. Signals from three pairs of fine wire electrodes placed high, middle, and low in the palatoglossus muscle of five speakers of American English were amplified, rectified, and integrated. The data were analyzed statistically to determine the patterns of similarity and degree of independence among simultaneous signals from different sites in the muscle for a given speaker. The middle signal was most often the best, and the low signal was most often the poorest representative of the group of signals. The greatest similarity was found between the high and middle signals; next most similar were the middle and low signals. Similarity between signals varied with utterance. In some cases, the relationship between two signals varied over time. This variation may be due to change in interelectrode distance during anisometric contraction or to different motor unit firing patterns.