Facial electromyography (fEMG) is an accurate and sensitive method capable of quantifying emotional processing and expression. Elementary emotions like; surprise, startle responses, disgust, fear, anger, sadness and happiness can be quantified via fEMG protocols.
In contrast to EDA / SCR, emotional valence and not just strength of response can be inferred from fEMG as distinct facial muscle groups are involved in the processing of different emotions.
A combined and integrated approach of both EDA and fEMG can be extremely revealing in providing a more comprehensive picture of emotional processing in response to specific stimuli. fEMG also has the advantage with being a faster emotional response than many other psychophysiological responses. For example, visual startle responses recorded from the orbicularis oculi muscles can have an onset latency of between 21ms - 120ms, with other more emotional responses detectable 80ms-200ms after stimuli onset. Variables of interest from fEMG can be seen as being either relating to amplitude parameters (strength of response) or time-based parameters (when something occurs in the response).
Typical dependent variables from fEMG include, response latency, rise time, peak response (amplitude / magnitude), response duration, response area (under the curve). Temporal parameters can be delineated from the raw signal, whereas amplitude parameters need to be calculated from a transformed (i.e., RMS or integrated) signal.