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Poster A48, Tuesday, August 20, 2019, 10:15 am – 12:00 pm, Restaurant Hall

Reducing the visual resolution of lexical signs increases working memory load

Josefine Andin1, Emil Holmer1, Krister Schönström2, Mary Rudner1;1Linköping University, Sweden, 2Stockholm University

Degrading the sound quality of words increases working memory (WM) load in the speech domain. To investigate the potential generalization of this effect across the language modalities of sign and speech, we studied the effect of reducing the visual resolution of lexical signs on WM load. In a functional Magnetic Resonance Imaging (fMRI) study, 16 deaf early proficient users of Swedish Sign Language (SSL) and 22 hearing non-signers performed an n-back WM task based on signs lexicalized in SSL. The resolution of the video-recorded sign stimuli was manipulated. Thus, sign stimuli were either clear or degraded. There were three levels of WM load in the n-back task achieved by manipulating n=1, 2 or 3. All participants had normal or corrected-to-normal visual acuity and contrast sensitivity. Due to recruitment constraints, the signers included in the analysis were significantly older than the non-signers. However, there was no difference between groups in non-verbal intelligence. ANOVA of n-back performance collected in the scanner showed no difference between groups. However, performance was poorer across groups when stimuli were degraded compared to when they were clear and when WM load was greater. There was a significant interaction between visual resolution and WM load such that the effect of stimulus degradation was greater when load was greater but there was no interaction with group. These behavioural results generalize the effect of stimulus degradation to sign language. Whole brain fMRI analysis showed increasing activation of the fronto-parietal WM network as load increased. WM processing of clear compared to degraded stimuli led to greater activation of the ventral visual stream and the opposite contrast led to greater activation of the dorsal visual stream. Further, non-signers compared to signers showed greater activation in the dorsal visual stream while signers compared to non-signers showed more activation in the superior temporal lobe. This pattern of results shows that WM for signs is sensitive to both load and visual resolution irrespective of sign language knowledge. In particular, it suggests that WM for degraded or less well represented signs (in non-signers) is less reliant on identification in the ventral stream and more reliant on localization in the dorsal stream. Results also confirm previous findings of differences between deaf signers and hearing individuals in the engagement of superior temporal cortex during a visual cognitive task.

Themes: Signed Language and Gesture, Control, Selection, and Executive Processes
Method: Functional Imaging

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