Time will tell: deficits of temporal information processing in patients with visual field loss

Visual field loss after brain lesions is commonly determined using perimetric tests of light detection (perimetry). Many patients with visual field defects complain about perceptual difficulties in areas that are perimetrically normal. To look at a potential cause for such difficulties, we topographically determined temporal characteristics of visual information processing in those patients and compared them to those of healthy subjects. In nine patients with visual field loss we measured thresholds of double-pulse resolution (DPR), i.e., the minimum perceivable duration of a temporal gap between two light pulses, at eccentricities up to 20°. Furthermore, high-resolution maps of visual reaction times (RT) were obtained in a computer-based campimetric test. Performance was compared to healthy controls from a cross-sectional study of temporal perception across the life span (Toelz Temporal Topography Study). Compared to healthy subjects, DPR thresholds and RTs in patients are elevated in the entire visual field, including areas that are perimetrically intact. Performance on temporal variables depends on the degree of intactness of the respective visual field position. DPR thresholds correlate considerably with RTs, and both parameters increase with eccentricity. However, whereas DPR thresholds are increased around blind regions relative to the intact field, this is not the case for RTs. Temporal processing in patients with cerebral vision loss is impaired to a certain extent independently from perimetric light detection performance. This may partly explain reported subjective perceptual problems. The findings may have important implications for visual rehabilitation, i.e., the potential generalization of light detection training to temporal processing performance.