Symmetry as a grouping cue for numerosity perception

To estimate the number of objects in an image, each element needs to be segregated as a single unit. Several principles guide the process of element identification, one of the strongest being symmetry. In the current study, we investigated how symmetry affects the ability to rapidly estimate the number of objects (numerosity). Participants judged the numerosity of asymmetric or symmetric arrays of various numerosities. The results show that the numerosity of symmetrical arrays was significantly underestimated at low numerosities, but the effect was greatly reduced at higher numerosities. Adding an additional axis of symmetry (double symmetry) further reduced perceived numerosity. The magnitude of the symmetry-driven underestimation was inversely correlated with autistic personality traits, consistent with previous work associating autistic traits with perceptual grouping. Overall, these results support the idea that perceived numerosity relies on object segmentation and grouping cues, with symmetry playing a key role.

Automated summary

This study investigated the influence of symmetry on estimating the number of objects. The results revealed that symmetrical arrays were underestimated at lower numbers and adding double symmetry further reduced perceived numerosity. The magnitude of the underestimation driven by symmetry was inversely related to autistic personality traits. Overall, these findings support the idea that perceived numerosity relies on object segmentation and grouping cues, with symmetry playing a key role.