Simple Spans in Deaf Signers and Hearing Non-Signers

Short-term memory is traditionally assessed by digit span tests. Deaf signers (DS) have repeatedly been reported to perform at lower levels on this test than hearing non-signers (NH [3]), despite equal performance on more complex working memory tasks and other cognitive tasks. Hearing signers have also been shown to perform at lower levels when they are tested on sign language compared to spoken language,suggesting that the differences between DS and HN are dependent on language rather than on deafness per se [4,7]. Sign languages are the natural mode of communication for many deaf persons and are fully fledged languages that can be described using the same terminology as spoken language [8]. That means that sign languages have phonology, morphology, syntax and prosody as well as their own grammar and vocabulary. However, there are some differences between spoken and signed languages that might influence short-term memory. Four commonly proposed explanations for these differences are (1) articulation rate, (2) phonological similarity effects, (3) differences in sensory memory traces and (4) temporal order effects: It has been suggested that short-term memory is restricted to the amount of words that can be articulated within two seconds [2]. Given that individual signs take longer to articulate than individual spoken words, this might affect rehearsal rate. According to the phonological similarity effect, items that are phonologically similar encode similar traces in the phonological loop, giving rise to