Assessing Higher-Order Visual Processing in Cerebral Visual Impairment Using Naturalistic Virtual-Reality-Based Visual Search Tasks

Abstract

Cerebral visual impairment (CVI) is a brain-based disorder associated with the maldevelopment of central visual pathways. Individuals with CVI often report difficulties with daily visual search tasks such as finding a favorite toy or familiar person in cluttered and crowded scenes. We developed two novel virtual reality (VR)-based visual search tasks combined with eye tracking to objectively assess higher order processing abilities in CVI. The first (virtual toybox) simulates a static object search, while the second (virtual hallway) represents a dynamic human search task. Participants were instructed to search for a preselected target while task demand was manipulated with respect to the presence of surrounding distractors. We found that CVI participants (when compared to age-matched controls) showed an overall impairment with visual search on both tasks and with respect to all gaze metrics. Furthermore, CVI participants showed a trend of worsening performance with increasing task demand. Finally, search performance was also impaired in CVI participants with normal/near normal visual acuity, suggesting that reduced stimulus visibility alone does not account for these observations. This novel approach may have important clinical utility in helping to assess environmental factors related to functional visual processing difficulties observed in CVI.

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

“…Successful fixation was defined as sustained gaze that remained within the outer contour of the target for a minimum time of 400 msec. Reaction time corresponded to the time needed to find the target on the screen and was defined as the first moment the participant’s gaze arrived within the outer contour of the target and remained fixated for at least 400 msec 40,41 . Gaze error was a continuous measure of a participant’s ability to locate and accurately fixate the target 40,41 .…”

“…The behavioral task was a static object visual search based on a previously designed desktop VR-based naturalistic environment called the "virtual toybox" (complete details regarding task design can be found in 40 , see also 41 ). Briefly, the task represented a simulated rendering of a toybox viewed from an overhead, first-person perspective.…”

“…Reaction time corresponded to the time needed to find the target on the screen and was defined as the first moment the participant's gaze arrived within the outer contour of the target and remained fixated for at least 400 msec 40,41 . Gaze error was a continuous measure of a participant's ability to locate and accurately fixate the target 40,41 . This accuracy measure was defined as the distance between the center of the target and the participant's gaze position and computed based on the sampling rate of the eye-tracker (90 Hz).…”

“…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][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45].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.…”

“…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][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45].…”