VISUAL EXPERIENCE SHAPES ARM POSITION SENSE IN INTERNAL AND EXTERNAL REFERENCE FRAMES AND ASSOCIATED CORTICAL LOAD

The ability to accurately perceive arm position is essential for motor control and depends on the integration of proprioceptive and visual information. However, how lifelong visual impairment (VI) affects position sense and its neural correlates remains unclear. We quantified arm position sense and associated cognitive-motor load in right-handed visually impaired (n = 7) and normally sighted (NS; n = 7) individuals using three bilateral arm position matching tasks: joint angle matching (JAM; internal coordinates), hand direction-distance matching (DDM; external coordinates), and mirror direction-distance matching (MDDM; external coordinates kinematically identical to JAM). Cognitive load was assessed using the contingent negative variation (CNV) from EEG recordings. VI participants exhibited reduced accuracy and precision of arm position sense in most conditions, and greater CNV magnitude, particularly in the left parietal cortex. Across both groups, performance was worse and CNV magnitude was greater in the DDM task compared with JAM, whereas JAM and MDDM yielded similar behavioral and neural outcomes. These findings indicate that (i) visual experience enhances arm position sense, and (ii) representing limb position in external coordinates imposes greater cognitive demands than encoding joint-based posture. The similarity between JAM and MDDM suggests that participants preferentially rely on internal representations when task kinematics permit.