Cross-modal localization in hemianopia: new insights on multisensory integration

To examine the possibility that the superior colliculus (SC) in patients with visual deficits can influence visual processes through multisensory stimulation of audiovisual stimuli.

Protocol

The patient sits 70 cm in front of the device. While maintaining the fixation point at the center, they must direct their gaze toward the presented stimuli and verbally report seeing them. Unimodal visual stimuli, unimodal auditory stimuli, and bimodal stimuli (audio and sound spatially and temporally coincident or non-coincident) are presented. 15 blocks concentrated over 2 consecutive days.

Results

In the blind field of hemianopic patients, the visual stimulus influences auditory localization only when the two stimuli are temporally and spatially coincident. Visual stimuli in the intact hemisphere induced a strong visual bias in auditory localization, regardless of spatial disparities, even when the two stimuli were temporally offset.

These results suggest that hidden visual processes remain active even in hemianopic subjects, although they differ in the intact hemisphere compared to the deficient one. It is thought that the enhancement of visual abilities depends on the superior colliculus, while visual bias is linked to geniculo-striate circuits.