Startle Reflex Modulation is the most appropriate way to quantify the effect of an external stimulus on internal emotion
The human eyeblink reflex, which occurs as a consequence of short and loud acoustic noise, represents a so-called startle reflex. In this case, the startle reflex is meant to protect the eye from potential environmental harm. Usually, a reflex is a very basic and automatic process. However, in humans it has been demonstrated that the very subjective emotional state correlates with the strength of this automatic response (e.g. Bradley et al., 1988; Lang et al., 1990). Consequently, the varying emotional state of a person is mirrored in startle reflex modulation (the more positive the emotional state the smaller the response). Strikingly, the eyeblink startle reflex is nothing but a muscle contraction closing the eye to protect it (musculus orbicularis oculi, circular muscle around the eye). So-called electromyography (EMG) allows you to quantify the grade of muscle contraction by measuring potential changes (in microvolt units) which directly correlate with contraction strength. Hence, by using appropriate analysing methods, it is possible to display the subjective emotional state related to any external stimulus by measuring muscle contraction. Controlled stimulation therefore enables the quantification of subjective emotional state in relation to distinct products, pictures, smells, etc. Finally, it is important to mention that this approach works without requiring a conscious feedback (such as a questionnaire) of the person being tested.
(text copyright: Peter Walla)
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Bradley, M.M., Cuthbert, B.N., and Lang, P.J. (1988). Lateral presentation of acoustic startle stimuli in a varying affective foreground. Psychophysiology, 25: 436.
Lang, P.J., Bradley, M.M., and Cuthbert, B.N. (1990). Emotion, Attention, and the Startle Reflex. Psychological Review, 97(3): 377-395.
picture: modified after: "Atlas der Anatomie des Menschen" (Tillmann), Springer-Lehrbuch, 2005.