Abstract
Faces are the most commonly used stimuli to study emotions. Researchers often manipulate the emotion contents and facial features to study emotion judgment, but rarely manipulate low-level stimulus features such as face sizes. Here, I investigated whether a mere difference in face size would cause differences in emotion judgment. Subjects discriminated emotions in fear-happy morphed faces. When subjects viewed larger faces, they had an increased judgment of fear and showed a higher specificity in emotion judgment, compared to when they viewed smaller faces. Concurrent high-resolution eye tracking further provided mechanistic insights: subjects had more fixations onto the eyes when they viewed larger faces whereas they had a wider dispersion of fixations when they viewed smaller faces. The difference in eye movement was present across fixations in serial order but independent of morph level, ambiguity level, or behavioral judgment. Together, this study not only suggested a link between emotion judgment and eye movement, but also showed importance of equalizing stimulus sizes when comparing emotion judgments.
Highlights
Faces are the most commonly used stimuli to study emotions
This difference was present across fixations in serial order, but independent of the morph level, ambiguity level, and behavioral judgment
I found that subjects had a significantly smaller xhalf for large faces compared to small faces (Fig. 1D; large: 48.2 ± 5.09, small: 51.3 ± 5.90; paired two-tailed t-test: t(22) = 3.65, P = 0.0014, effect size in Hedges’ g: g = 0.56), suggesting that they were more likely to judge faces as fearful when viewing large faces
Summary
Faces are the most commonly used stimuli to study emotions. Researchers often manipulate the emotion contents and facial features to study emotion judgment, but rarely manipulate low-level stimulus features such as face sizes. A recent computational framework with novel spatiotemporal analyses of eye movements has provided theoretical insights and empirical evidence for the computational mechanisms underlying perception of facial expressions[23] This framework has revealed culture-specific decoding strategies of facial expressions, arguing against the universality of human facial expressions of emotion[24]. Concurrent eye tracking further provided insights into the underlying mechanism: more fixations were directed to the eyes when people viewed larger faces whereas there was a wider spatial dispersion of fixations when people viewed smaller faces. This difference was present across fixations in serial order, but independent of the morph level, ambiguity level, and behavioral judgment. This study suggested a link between emotion judgment and eye movement, and showed importance of choosing stimulus size to study emotion judgment
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