Abstract
Lateralized post-chiasmatic lesions of the primary visual pathway result in loss of visual perception in the field retinotopically corresponding to the damaged cortical area. However, patients with visual field defects have shown enhanced detection and localization of multisensory audio-visual pairs presented in the blind field. This preserved multisensory integrative ability (i.e., crossmodal blindsight) seems to be subserved by the spared retino-colliculo-dorsal pathway. According to this view, audio-visual integrative mechanisms could be used to increase the functionality of the spared circuit and, as a consequence, might represent an important tool for the rehabilitation of visual field defects. The present study tested this hypothesis, investigating whether exposure to systematic multisensory audio-visual stimulation could induce long-lasting improvements in the visual performance of patients with visual field defects. A group of 10 patients with chronic visual field defects were exposed to audio-visual training for 4 h daily, over a period of 2 weeks. Behavioral, oculomotor and electroencephalography (EEG) measures were recorded during several visual tasks before and after audio-visual training. After audio-visual training, improvements in visual search abilities, visual detection, self-perceived disability in daily life activities and oculomotor parameters were found, suggesting the implementation of more effective visual exploration strategies. At the electrophysiological level, after training, patients showed a significant reduction of the P3 amplitude in response to stimuli presented in the intact field, reflecting a reduction in attentional resources allocated to the intact field, which might co-occur with a shift of spatial attention towards the blind field. More interestingly, both the behavioral improvements and the electrophysiological changes observed after training were found to be stable at a follow-up session (on average, 8 months after training), suggesting long-term effects of multisensory audio-visual training. These long-lasting effects seem to be subserved by the activation of the spared retino-colliculo-dorsal pathway, which promotes orienting responses towards the blind field, able to both compensate for the visual field loss and concurrently attenuate visual attention towards the intact field. These results add to previous findings the knowledge that audio-visual multisensory stimulation promote long-term plastic changes in hemianopics, resulting in stable and long-lasting ameliorations in behavioral and electrophysiological measures.
Highlights
Visual field defects, resulting from damage to the visual structures located behind the chiasma, including primary visual cortex (V1), surrounding extrastriate cortices and optic radiations, consist of a loss of visual perception in up to one half of the visual field
These findings suggest that cross-modal facilitation occurs outside conscious vision and, importantly for the present study, that it may boost the processing of visual stimuli presented in the blind field (Bolognini et al, 2005; Passamonti et al, 2009; for a review, see Làdavas, 2008)
Given that the P3 amplitude reflects the amount of attention allocated to stimulus processing (Isreal et al, 1980; Johnson, 1984, 1986), these results suggest a critical role for multisensory audio-visual treatment in reducing attentional processing of stimuli presented in the intact field
Summary
Visual field defects, resulting from damage to the visual structures located behind the chiasma, including primary visual cortex (V1), surrounding extrastriate cortices and optic radiations, consist of a loss of visual perception in up to one half of the visual field. There was a significant improvement in visual detection of stimuli presented in the blind field when they were concurrently presented with spatially coincident auditory stimuli (Frassinetti et al, 2005) These findings suggest that cross-modal facilitation occurs outside conscious vision and, importantly for the present study, that it may boost the processing of visual stimuli presented in the blind field (Bolognini et al, 2005; Passamonti et al, 2009; for a review, see Làdavas, 2008). The training promoted a reduction in self-perceived disability in daily life activities, confirming a transfer of the effects of training to ecological environments (Bolognini et al, 2005; Passamonti et al, 2009)
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