Susceptibility to spatial illusions does not depend on visual experience: Evidence from sighted and blind children

Visuospatial illusions may be a by-product of learned regularities in the environment or they may reflect the recruitment of sensory mechanisms that, in some contexts, provide an erroneous spatial estimate. Young children experience visual illusions, and blind adults are susceptible using touch alone, suggesting that the perceptual inferences influencing illusions are amodal and rapidly acquired. However, other evidence, such as visual illusions in the newly sighted, points to the involvement of innate mechanisms. To help tease apart cognitive from sensory influences, we investigated susceptibility to the Ebbinghaus, Müller-Lyer and Vertical-Horizontal illusions in children aged 6-14 years following visual-only, haptic-only and bimodal exploration. Consistent with previous findings, children of all ages were susceptible to all three visual illusions. In addition, illusions of extent but not of size were experienced using haptics alone. We then tested 17 congenitally blind children to investigate whether illusions were mediated by vision. Similar to their sighted counterparts, blind children were also susceptible to illusions following haptic exploration suggesting that early visual experience is not necessary for spatial illusions to be perceived. Reduced susceptibility in older children to some illusions further implies that explicit or formal knowledge of spatial relations is unlikely to mediate these experiences. Instead, the results are consistent with previous evidence for cross-modal interactions in 'visual' brain regions and point to the possibility that illusions may be driven by innate developmental processes that are not entirely dependent on, although are refined by, visual experience.