Perceptual invariance or orientation specificity in American Sign Language? Evidence from repetition priming for signs and gestures
Repetition priming has been successfully employed to examine stages of processing in a wide variety of cognitive domains including language, object recognition, and memory. This study uses a novel repetition priming paradigm in the context of a categorisation task to explore early stages in the processing of American Sign Language signs and self-grooming gestures. Specifically, we investigated the degree to which deaf signers’ and hearing nonsigners’ perception of these linguistic or nonlinguistic actions might be differentially robust to changes in perceptual viewpoint. We conjectured that to the extent that signers were accessing language-specific representations in their performance of the task, they might show more similar priming effects under different viewing conditions than hearing subjects. In essence, this would provide evidence for a visually based “lack of invariance” phenomenon. However, if the early stages of visual-action processing are similar for deaf and hearing subjects, then no such difference should be found.
Most bilinguals understand their second language more slowly than their first. This behavioral asymmetry may arise from the perceptual, phonological, lexicosemantic, or strategic components of bilingual word processing. However, little is known about the neural source of such language dominance and how it is regulated in the bilingual brain. Using functional magnetic resonance imaging, we found that unconscious neural priming in bilingual word recognition is language nonselective in the left midfusiform gyrus but exhibits a preference for the dominant language in the left posterior middle temporal gyrus (MTG). These early-stage components of reading were located slightly upstream of the left midlateral MTG, which exhibited enhanced response during a conscious switch of language. Effective connectivity analysis revealed that this language switch is triggered by reentrant signals from inferior frontal cortex and not by bottom–up signals from occipitotemporal cortex. We further confirmed that magnetic stimulation of the same inferior frontal region interferes with conscious language control but does not disrupt unconscious priming by masked words. Collectively, our results demonstrate that the neural bottleneck in the bilingual brain is a cross-language asymmetry of form–meaning association in inferolateral temporal cortex, which is overcome by a top–down cognitive control for implementing a task schema in each language.
from Cerebral Cortex