Crossmodal enhancement of visual orientation discrimination by looming sounds requires functional activation of primary visual areas: A case study

Abstract

Approaching or looming sounds are potentially threatening stimuli with particular impact on visual processing. The early onset of crossmodal effects by looming sounds (Romei et al., 2009) and their impact on low-level visual processing (Leo et al., 2011) suggests that these interactions may take place already within low-level visual cortices. To investigate the contribution of early visual areas in mediating the effects of looming sounds on visual processing, we tested a patient with bilateral occipital lesion and spared residual portions of V1/V2 (SDV). Accordingly, SDV’s visual perimetry revealed blindness of the central visual field with some residual peripheral vision. We tested the influence of looming, receding and static sounds on SDV line discrimination ability in the relatively preserved visual field or in the blind visual field. We found that SDV’s visual orientation sensitivity was significantly enhanced when visual stimuli were paired with looming sounds, compared to other types of sound or presented alone. Crucially, this selective crossmodal effect was found when visual stimuli were presented in the relatively preserved visual field whereas no modulation in visual orientation sensitivity was found for stimuli presented in the blind visual field. These results provide direct evidence that primary visual areas are critically involved in crossmodal modulation of visual sensitivity and that, in the presence of V1 lesion, visual pathways (e.g., retino-colliculo-extrastriate) bypassing V1 can mediate the crossmodal enhancement of basic visual abilities such as detection of spots of lights (Ladavas, 2008), but not more complex functions such as line orientation discrimination.