Deaf signers use magnitude manipulatioin strategies for mulitplication : fMRI evidence

Evidence suggests that the lag reported in mathematics for deaf signers derives from difficulties related to the verbal system of number processing as described in the triple code model. For hearing individuals the verbal system has been shown to be recruited for both arithmetic and language tasks. In the present study we investigate for the first time neuronal representations of arithmetic in deaf signers. We examine if the neural network supporting arithmetic and language, including the horizontal portion of the intraparietal sulcus (HIPS), the superior parietal lobule (SPL) bilaterally, the left angular gyrus (AG), pars opercularis (POPE) and pars triangularis (PTRI) of the left inferior frontal gyrus (IFG), is differently recruited for deaf and hearing individuals. Imaging data were collected from 16 deaf signers and 16 well-matched hearing nonsigners, using the same stimulus material for all tasks, but with different cues. During multiplication, deaf signers recruited rHIPS more than hearing non-signers, suggesting greater involvement of magnitude manipulation processes related to the quantity system, whereas there was no evidence that the verbal system was recruited. Further, there was no support for the notion of a common representation of phonology for sign and speech as previously suggested.