Size-invariant facial expression categorization and associated gaze allocation within social interaction space

K Guo

School of Psychology, University of Lincoln, United Kingdom

As faces often appear under very different viewing conditions (e.g. brightness, viewing angle or distance), invariant facial information recognition is a key to our social interactions. Despite we would clearly benefit from differentiating different facial expressions (e.g. anger vs happy) at a distance, there is surprisingly little research examining how expression categorization and associated gaze allocation is affected by viewing distance in the range of typical social space. In this study we systematically varied the size of faces displaying six basic facial expressions of emotion with varying intensities to mimic viewing distance ranging from arm-length to 5 meters, and employed a self-paced expression categorization task to measure participants' categorization performance and associated gaze patterns. Irrespective of the displayed expression and its intensity, the participants showed indistinguishable categorization accuracy and reaction time across the tested face sizes. Reducing face size would decrease the number of fixations directed at the faces but increase individual fixation duration, and shift gaze distribution from scanning all key internal facial features to mainly fixating at central face region. Our results suggest a size-invariant facial expression categorization behavior within social interaction distance which could be linked to a holistic gaze strategy for extracting expressive facial cues.

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