Poster B61, Thursday, August 16, 3:05 – 4:50 pm, Room 2000AB
Examining the effect of language experience on plasticity in superior temporal cortices in deaf and hearing signers
Tae Twomey1, Dafydd Waters1, Cathy Price1, Mairéad MacSweeney1;1University College London
It has been clearly demonstrated that parts of the superior temporal cortex (STC) are activated more in deaf than hearing people. In particular, these differences are reliably observed when sign language stimuli are used. It follows from this therefore that the duration of experience with sign language might also influence the extent of plasticity observed in STC. Here we manipulated sign language experience by testing participants who acquired British Sign Language (BSL) at difference ages. We predicted that in addition to a main effect of hearing status in the STC (deaf > hearing) during perception of sign language, there would be a hearing status X age of BSL acquisition interaction. Specifically we predicted a greater effect of deafness in STC (D >H) in early learners than late learners of BSL. A second question relates to the impact of early language experience in deaf people only. We have previously reported greater activation in left inferior frontal gyrus (IFG) in deaf late than deaf early signers during BSL phonological judgment using picture stimuli (MacSweeney et al., 2008). We investigated whether the same effect was observed during a task, which unlike the BSL phonological judgement, did not require meta-linguistic analyses and visuospatial working memory. We tested deaf and hearing signers who learnt BSL either early (native) or late in life (after the age of 15 years): four groups, N=52 in total. The groups were matched on performance on a BSL grammaticality judgment test (Cormier et al., 2012). We collected fMRI data as they detected a semantic anomaly in BSL sentences; and a target (the signer touching the nose) in strings of nonsense gestures. As predicted, a main effect of hearing status (deaf > hearing) was found in the STCs bilaterally, replicating previous findings. This effect was centred on Heschl’s gyrus and extended to planum polare anteriorly and planum temporale posteriorly. Relative to rest, hearing signers showed deactivation whereas deaf signers showed activation. However, these responses within each group were not significantly different from rest. Interestingly, when the nonsense gesture stimuli were used as a baseline, the group difference disappeared. This was because STC responses to BSL and gesture within deaf signers (activation) and hearing signers (deactivation) showed a very similar pattern (BSL>gesture). Moreover, contrary to our predictions, the interaction between hearing status and age of BSL acquisition was not significant, irrespective of baseline. With regard to our second question, there were no significant differences in left IFG activation between deaf late and deaf early signers. This suggests that the previously observed effects of late sign language acquisition in deaf signers, are likely to be task-dependent. The current study demonstrates the importance of the baseline in testing for crossmodal plasticity: an obvious but often overlooked point. Our findings also suggest that plasticity in the parts of STCs identified here is primarily driven by deafness and it not influenced, to any great extent, by age of sign language acquisition or linguistic status of the input.
Topic Area: Signed Language and Gesture