Patient RP suffers a unilateral right homonymous quadrant anopia but demonstrates better than chance discrimination for stimuli presented in the blind field at temporal frequencies between 33 and 47 Hz . Examination of her reports of visual experience during blind-field discrimination suggests a more complex picture in which experiences particular to correct discrimination are not found at low-mid-gamma frequencies, but are significantly more likely than average at a lower frequency at which blindsight is not observed. We believe that visual experience (...) may serve to support blindsight if discrimination tasks are generally impaired at frequencies outside of the low-mid-gamma band. If this is so, although generally experienced as non-specific and unstructured light, the visual experience that accompanies discrimination performance must be based upon a neural representation which includes information on the visual features present in the stimulus. (shrink)

Abstract. A rhesus monkey, Helen, from whom the striate cortex was almost totally removed, was studied intensively over a period of 8 years. During this time she regained an effective, though limited, degree of visually guided behaviour. The evidence suggests that while Helen suffered a permanent loss of `focal vision she retained (initially unexpressed) the capacity for `ambient vision.

The issue of how basic sensory and temporal processing are related is still unresolved. We studied temporal processing, as assessed by simple visual reaction times (RT) and double-pulse resolution (DPR), in patients with partial vision loss after visual pathway lesions and investigated whether vision restoration training (VRT), a training program designed to improve light detection performance, would also affect temporal processing. Perimetric and campimetric visual field tests as well as maps of DPR thresholds and RT were acquired before and after (...) a 3 months training period with VRT. Patient performance was compared to that of age-matched healthy subjects. Intact visual field size increased during training. Averaged across the entire visual field, DPR remained constant while RT improved slightly. However, in transition zones between the blind and intact areas (areas of residual vision) where patients had shown between 20 and 80% of stimulus detection probability in pre-training visual field tests, both DPR and RT improved markedly. The magnitude of improvement depended on the defect depth (or degree of intactness) of the respective region at baseline. Inter-individual training outcome variability was very high, with some patients showing little change and others showing performance approaching that of healthy controls. Training-induced improvement of light detection in patients with visual field loss thus generalized to dynamic visual functions. The findings suggest that similar neural mechanisms may underlie the impairment and subsequent training-induced functional recovery of both light detection and temporal processing. (shrink)