Breakdown of holistic face processing with vertical displacement: a consequence of disrupted perceptual grouping, not biological implausibility

Holistic processing is a fast, efficient, and seemingly effortless processing style typically linked with perceiving faces and objects of expertise—where observers appear unable to selectively attend to features within a stimulus. Holistic face processing is disrupted when the top and bottom halves are vertically separated by a substantial amount. This was attributed to the biological implausibility of the elongated faces—a domain-specific explanation. However, more recent findings of face-like holistic processing of stimuli with strong perceptual grouping cues suggest that such cues support holistic processing more generally. If so, the breakdown of holistic processing with vertical separation may reflect a disruption to perceptual grouping mechanisms rather than to face-specific mechanisms. We tested this hypothesis across three experiments. Experiment 1 used a modified composite part matching paradigm to replicate previous results—vertically separating the halves in a composite face paradigm disrupted holistic face processing. Experiment 2 demonstrated that vertical part displacement similarly disrupted holistic processing of non-face stimuli rich in perceptual grouping cues, which are not constrained by biological plausibility. Experiment 3 revealed that horizontal misalignment—a standard method of disrupting holistic processing—does not further diminish holistic processing of vertically displaced non-face stimuli, consistent with the interpretation that holistic processing was already disrupted for these stimuli. These findings support a disrupted perceptual grouping, rather than biological implausibility, account of the disruption to face holistic processing with vertical part misalignment. This has implications for understanding face processing and, given the role of holistic perception in supporting perceptual expertise, skilled perception more broadly.