Perception of Activity in the Zygomaticus Major and Corrugator Supercilii Muscle Regions

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Abstract
This study was designed to assess differences in perception of activity in the zygomaticus major (predominant during smiling) and corrugator supercilii facial muscles (predominant during frowning). Magnitude production psychophysical methods were used to relate subjective intensity to objective electromyographic activity using a psychophysical power function under four conditions: smiling, frowning, smiling concurrent with maintenance of a frown, and frowning concurrent with maintenance of a smile. High correlation coefficients for each power function for both zygomatic and corrugator activity were obtained. Differences in sensitivity evaluated by comparing the exponent for slope of the power functions showed differences across the muscles and as a function of the conditions. The exponent for frowning was greater than for smiling. Although the exponent for zygomatic activity was similar with and without frowning, significantly greater exponents were shown for corrugator activity when concurrently frowning and smiling than when only frowning. Maximal electromyographic activity was greater in the zygomaticus major muscle during smiling than in the corrugator supercilii muscle during frowning. These results provide a methodology for perception of electromyographic activity which could be a useful basis for analysis of the role of perception in regulating affect.