Contactless differentiation of pleasant and unpleasant valence: Assessment of the acoustic startle eyeblink response with infrared reflectance oculography.

The ability to distinguish between discrete emotions by monitoring autonomic or facial features has been an elusive "holy grail" for fields such as psychophysiology, affective computing, and human-computer interface design. However, cross-validated models are lacking, and contemporary theory suggests that emotions may lack distinct physiological or facial "signatures." Therefore, in this study, we propose a reorientation toward distinguishing between pleasant and unpleasant affective valence. We focus on the acoustic eyeblink response, which exhibits affective modulation but remains underutilized. The movement of the eyelid was monitored in a contactless manner via infrared reflectance oculography at 1 kHz while 36 participants viewed normatively pleasant, neutral, and unpleasant images, and 50-ms bursts of white noise were presented binaurally via headphones. Startle responses while viewing pleasant images exhibited significantly smaller amplitudes than those while viewing unpleasant images, with a large effect size (d = 1.56). The affective modulation of the eyeblink startle response is a robust phenomenon that can be assessed in a contactless manner. As research continues on whether systems based on psychophysiological or facial features can distinguish between discrete emotions, the eyeblink startle response offers a relatively simple way to distinguish between pleasant and unpleasant affective valence.