Understanding boundary extension: Normalization and extension errors in picture memory among adults and boys with and without Asperger's syndrome

Boundary extension is the tendency for people to “remember” information that fell outside a picture's boundaries. We used a novel test of boundary extension to provide absolute estimates of the magnitude of extension errors and of the degree to which people are influenced by the way a picture is presented at the time of testing. Participants were shown photographs on a computer and subsequently allowed to adjust their magnification to match the size they remembered. The test produced reliable boundary extension of around 11% in adults and large influences of initial test size. In a second experiment we tested boys diagnosed with Asperger's syndrome and matched controls. Both groups demonstrated boundary extension comparable to that observed in adults but greater effects of initial test size. High performance IQ in Asperger's was linked with high levels of boundary extension, while for the matched control group the opposite pattern was obtained.