Not always in the eye of the beholder: How pupillary highlights modulate gaze perception in portraits.

Building on the robustness of perspective, which describes the observer’s tolerance for perspective distortions from the painter’s viewpoint, and the Mona Lisa effect which describes the phenomenon where a depicted gaze appears directed at the observer, we examined the role of pupillary highlights in modulating the perception of direct gaze in portraits, aiming to explore how these visual cues contribute to the impression of being looked at. Four online experiments were conducted via Qualtrics platform. Stimuli included classical painted portraits and photographic portraits of Hollywood Golden Age actors. In Experiment 1, unaltered portraits were presented and participants judged whether the figure appeared to be staring at them, enabling categorization into (a) clearly staring and (b) ambiguous or not staring. Experiment 2 introduced five pupillary highlight conditions (i.e. original, no highlights, highlights positioned left, centre, or right), with participants rating their impression of being stared at on a 5-point Likert scale. Experiments 3 and 4 replicated Experiment 2 but with either the left or right eye of each portrait occluded. Results showed, in Experiment 2, an inversion of gaze perception ratings for photographic portraits when highlights were removed. Across Experiments 3 and 4, the position of pupillary highlights significantly influenced the perceived direction of gaze, with effects differing according to which eye was occluded. These findings underline the critical role of pupillary highlights in gaze perception, modulating the observer’s impression of direct gaze in both painted and photographic portraits. Results support theoretical accounts of both robustness to perspective and the Mona Lisa effect, demonstrating how minimal image manipulations can alter socio-cognitive interpretations of visual stimuli.