Facial EMG

Facial electromyography (EMG) measures affect by recording the tiny electrical signals produced by facial muscles, providing an objective, continuous index of emotional valence and intensity that can detect reactions too subtle or fleeting to produce a visible expression. Cacioppo, Petty, Losch, and Kim showed in 1986 that activity over two muscle regions differentiates affect: the corrugator supercilii (the brow muscle that furrows in frowning) increases with negative affect, while the zygomaticus major (the cheek muscle that pulls in smiling) increases with positive affect, and amplitudes scale with the intensity of the reaction. Because surface electrodes capture muscle activity even when no overt expression occurs, facial EMG offers a sensitive, hard-to-fake measure of evaluative responses widely used in research on attitudes, emotion, persuasion, and social perception, often paired with reaction-time and self-report measures.