The inversion-induced size illusion generalizes to real child faces but is absent for cartoon child faces

Previous studies have revealed that inverted faces are perceived as physically larger than upright faces, called the inversion-induced size illusion—a phenomenon thought to arise from disrupted configural processing. It remains unclear whether this illusion generalizes across other face types (such as real child and cartoon child faces). Thirty Chinese university students completed a psychophysical size-comparison task using the method of constant stimuli under a simultaneous presentation paradigm with limited exposure duration. Experiment 1a replicated the classic inversion-induced size illusion with adult faces. Experiment 1b observed a comparable and significant illusion for real child faces, indicating that developmental differences in facial morphology do not abolish the effect. In contrast, no inversion-induced size illusion was observed for cartoon child faces. Direct comparisons revealed a larger magnitude of the size illusion effect for real child faces as compared to cartoon child faces. Together, these findings suggest that the inversion-induced size illusion is not a general property of all face-like stimuli. Instead, its occurrence appears to depend on specific stimulus characteristics under the present experimental conditions, including—but not necessarily limited to—the preservation of biologically plausible facial structure.