Altered Neural Oscillations Underlying Visuospatial Processing in Cerebral Visual Impairment (CVI)

Abstract

Visuospatial processing deficits are commonly observed in individuals with cerebral visual impairment (CVI) and even in cases where visual acuity and visual field functions are intact. CVI is a brain-based visual disorder associated with the maldevelopment of central visual pathways and structures. However, the neurophysiological basis underlying higher-order perceptual impairments in this condition has not been clearly identified, which in turn posits limits on rehabilitative interventions. Using combined eye tracking and electroencephalography (EEG) recordings, we assessed the profile and performance of visual search on a naturalistic virtual reality (VR)-based task. Participants with CVI and controls with neurotypical development were instructed to search, locate, and fixate a specific target placed among surrounding distractors at two levels of task difficulty. Analyzing evoked (time or phase-locked) and induced (not time or phase-locked) components of EEG activity allowed for feedforward and feedback processing mechanisms to be uncovered. We found that visual search performance in CVI was impaired compared to age-matched controls with neurotypical development (as indexed by outcomes of success rate, reaction time, and gaze error). Analysis of neural oscillations across a broad frequency band [4-55 Hz] revealed markedly reduced early-onset evoked theta [4-6 Hz] activity (within 0.5 sec) regardless of task difficulty. Moreover, while induced alpha activity increased with task difficulty in controls, this modulation was absent in the CVI group providing a potential neural correlate for their deficits with visual search and distractor suppression. Finally, CVI participants also showed an overall delayed and sustained induced gamma response [30-45 Hz]. We conclude that impaired visual search performance in CVI is associated with substantial alterations across a wide range of neural oscillation frequencies. This includes both evoked and induced components related to feedforward and feedback processing and implicating local and distributed levels of neural processing.