Making sense of an unexpected detrimental effect of sign language use in a visual task.

What supports deaf signers advantage over nonsigners on visuospatial short-term memory (STM) tasks is still a matter of debate. We compared the performance of 18 deaf Italian Sign Language (LIS) users with that of a matched group of Italian hearing nonsigners in three different tasks: two versions of the Corsi Block test, namely span forward and span backward, and the Visual Pattern Test (VPT). Although the Corsi forward and backward are dynamic and mainly involve a spatial component, the VPT is static and taps primarily the visual component of STM. Signers significantly outperformed nonsigners on both versions of the Corsi Block test, whereas they performed significantly worse on the VPT. We suggest that the source of the different pattern lies in the static nature of the VPT versus the dynamic nature of the Corsi spans.