Can you feel what you do not see? Using internal feedback to detect briefly presented emotional stimuli

Briefly presented (e.g., 10 ms) emotional stimuli (e.g., angry faces) can influence behavior and physiology. Yet, they are difficult to identify in an emotion detection task. The current study investigated whether identification can be improved by focusing participants on their internal reactions. In addition, we tested how variations in presentation parameters and expression type influence identification rate and facial reactions, measured with electromyography (EMG). Participants made force-choice identifications of brief expressions (happy/angry/neutral). Stimulus and presentation properties were varied (duration, face set, masking-type). In addition, as their identification strategy, one group of participants was instructed to use their bodily and feeling changes. One control group was instructed to focus on visual details, and another group received no strategy instructions. The results revealed distinct EMG responses, with greatest corrugator activity to angry, then neutral, and least to happy faces. All variations in stimulus and presentation properties had robust and parallel effects on both identification and EMG. Corrugator EMG was reliable enough to statistically predict stimulus valence. However, instructions to focus on the internal states did not improve identification rates or change physiological responses. These findings suggest that brief expressions produce a robust bodily signal, which could in principle be used as feedback to improve identification. However, the fact that participants did not improve with internal focus suggests that bodily and feeling reactions are either principally unconscious, or that other ways of training or instruction are necessary to make use of their feedback potential.

Research highlights
► Very briefly presented emotional faces elicit a corrugator response.
► Strength of the signal depends on emotion, face set, exposure time, and mask.
► Corrugator signal can be used to infer what stimulus has been presented.
► Simple instruction does not suffice to make subjects deliberately use these signals.