Previous research has shown that eyebrow movement during speech exhibits a systematic relationship with intonation: brow raises tend to be aligned with pitch accents, typically preceding them. The present study approaches the question of temporal alignment between brow movement and intonation from a new angle. The study makes use of footage from the Late Night Show with David Letterman, processed with 3D facial landmark detection. Pitch is modeled as a sinusoidal function whose parameters are correlated with the maximum height of the eyebrows in a brow raise. The results confirm some previous findings on audiovisual prosody but lead to new insights as well. First, the shape of the pitch signal in a region of approx. 630 ms before the brow raise is not random and tends to display a specific shape. Second, while being less informative than the post-peak pitch, the pitch signal in the pre-peak region also exhibits correlations with the magnitude of the associated brow raises. Both of these results point to early preparatory action in the speech signal, calling into question the visual-precedes-acoustic assumption. The results are interpreted as supporting a unified view of gesture/speech co-production that regards both signals as manifestations of a single communicative act.
Keywords: audiovisual prosody; eyebrows; facial gestures; pitch; prominence.