Association between high-frequency hearing sensitivity and visual cross-modal plasticity in typical-hearing adults

Visual cross-modal plasticity after deafness describes when auditory cortical regions increase responsiveness to visual stimulation. Such neuroplasticity demonstrates that sensory cortex adapts to profound peripheral impairment by upregulating healthy sensory function. However, whether cross-modal plasticity occurs for mild, partial hearing loss is less clear. Here we investigated cross-modal plasticity in "normal" hearing adults who had varying high-frequency hearing sensitivity, and if cross-modal plasticity was linked to adaptive visual behaviours. Twenty-five participants (aged 18 to 78) were tested in a modified Sternberg task with text-based visual words. Participants viewed a five-word sentence presented word-by-word during an encoding period and were asked to hold those words in short-term memory during a retention period. After, they reported if a target word probe was present in the encoding period. Multichannel EEG recorded visual cortical activity throughout. Results showed separate effects of high-frequency hearing sensitivity and age on visual cortical responses. At scalp sensors, visual N1 amplitudes were larger with worse hearing sensitivity, and P2 latencies were longer. In contrast, age was associated with shorter P2 latencies. Source analysis found that N1 amplitude increased with worse hearing sensitivity in right auditory cortex, but no effects were found in visual cortex, or for age. Hearing sensitivity and visual encoding activity did not correlate with behavioural performance or neural oscillations during the retention period. Results suggest for the first time that even a slight hearing decline in the high-frequency range is associated with higher visual activation of right auditory cortex, consistent with cross-modal plasticity.