AU1 — Inner Brow Raiser
The Action Unit produced by the medial frontalis, which lifts the inner corners of the brows. It does not establish sadness, distress, or concern.
AU1 raises the inner portions of the eyebrows, producing oblique forehead lines. Researchers have studied AU1 and AU1+4 in many expression contexts, but these movements do not verify sadness, worry, empathy, or distress.
AU1 is commonly studied in facial-movement research and may be included in FACS-based analytics systems.
Related terms: action unit, au4 brow lowerer, facial action coding system
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