At suprathreshold levels, detection and awareness of visual stimuli are typically synonymous in nonclinical populations. But following postgeniculate lesions, some patients may perform above chance in forced-choice detection paradigms, while reporting not to see the visual events presented within their blind field. This phenomenon, termed “blindsight,” is intriguing because it demonstrates a dissociation between detection and perception. It is possible, however, for a blindsight patient to have some “feeling” of the occurrence of an event without seeing per se. This is termed blindsight type II to distinguish it from the type I, defined as discrimination capability in the total absence of any acknowledged awareness. Here we report on a well-studied patient, D.B., whose blindsight capabilities have been previously documented. We have found that D.B. is capable of detecting visual patterns defined by changes in luminance (first-order gratings) and those defined by contrast modulation of textured patterns (textured gratings; second-order stimuli) while being aware of the former but reporting no awareness of the latter. We have systematically investigated the parameters that could lead to visual awareness of the patterns and show that mechanisms underlying the subjective reports of visual awareness rely primarily on low spatial frequency, first-order spatial components of the image.

Purpose. We investigated systematically the effect of repeated exposure on detection and reported awareness of visual stimuli presented deep within the field defect of 5 hemianopic patients. Methods. An objective measure of sensitivity (detection in a temporal two-alternative forced-choice paradigm) and subjective reports of awareness were recorded on trial by trial bases. Visual stimulus to be detected was a temporally modulated (10 Hz) circular patch (6° diameter) of vertical grating (1 c/°). Hemianopic patients took part in the study 8 to 15 months after injury, so that the findings could not be attributed to spontaneous recovery. Results. Initially, high contrast (90%) target stimuli were detected at or near chance level with little reported awareness. In 4 of 5 cases, repeated stimulation led to improved sensitivity, indicated by increased detection scores and higher incidence of awareness. In a fifth case, there was no change in sensitivity despite extensive exposure (>22,000 trials). Conclusions. At retinal locations deep within the field defect, repeated stimulation can lead to blindsight performance (type I detection without awareness), followed by detection with reported awareness (type II blindsight), and eventual reported visual experiences. The findings indicate that conscious awareness of stimuli lies on a continuous spectrum and repeated systematic training can lead to improved visual sensitivity.