Emotion recognition (sometimes) depends on horizontal orientations.

Face recognition depends critically on horizontal orientations (Goffaux & Dakin, Frontiers in Psychology, 1(143), 1-14, 2010): Face images that lack horizontal features are harder to recognize than those that have this information preserved. We asked whether facial emotional recognition also exhibits this dependency by asking observers to categorize orientation-filtered happy and sad expressions. Furthermore, we aimed to dissociate image-based orientation energy from object-based orientation by rotating images 90 deg in the picture plane. In our first experiment, we showed that the perception of emotional expression does depend on horizontal orientations, and that object-based orientation constrained performance more than image-based orientation did. In Experiment 2, we showed that mouth openness (i.e., open vs. closed mouths) also influenced the emotion-dependent reliance on horizontal information. Finally, we describe a simple computational analysis that demonstrates that the impact of mouth openness was not predicted by variation in the distribution of orientation energy across horizontal and vertical orientation bands. Overall, our results suggest that emotion recognition largely does depend on horizontal information defined relative to the face, but that this bias is modulated by multiple factors that introduce variation in appearance across and within distinct emotions.