Abstract
The spatial location of an object can be represented relative to two types of reference frames: allocentric and egocentric. The allocentric reference frame encodes object positions relative to another background object independent of observers’ body effectors while the egocentric reference frame encodes object positions relative to observers’ own body effectors. At the behavioral level, recent evidence from our lab suggested that congenital deafness is associated with significantly impaired (slowed) egocentric judgments, compared to the healthy hearing control group. It remains unclear, however, the neural mechanisms underlying the impaired egocentric judgements after early congenital deafness. Here, we investigated this issue by using structural, functional MRI, and diffusion tensor image (DTI). Behaviorally, we replicated previous behavioral evidence by showing that egocentric judgments were significantly slower than allocentric judgments in the congenitally deaf subjects while were comparable in the healthy hearing controls. At the neural level, compared to the hearing controls, the bilateral medial frontal gyrus in default mode network was specifically activated by the allocentric task, and the left superior parietal gyrus was specifically activated by the egocentric task in the deaf subjects. Structurally, by using T1-weighted MRI and surface-based morphometry of the gray matter, we found that the cortical thickness of the bilateral primary auditory cortex in the Heschl’s gyrus was thicker in the deaf than in the control group. Furthermore, by using DTI and tract-based spatial statistics of the white matter, we found that the mean fractional anisotropy values in the bilateral parietal cortex and the right temporal cortex were significantly reduced in the deaf group, compared to the hearing controls. Taken together, functional and structural neural evidence consistently suggested that the impaired egocentric spatial representations in the congenitally deaf subjects are associated with neural changes in the dorsal visual stream and the auditory cortex.
Acknowledgement: Natural Science Foundation of China grant Number 31871138 to QC