Blindsight patients with damage to the visual cortex can discriminate objects but report no conscious visual experience. This provides an intriguing opportunity to allow the study of subjective awareness in isolation from objective performance capacity. However, blindsight is rare, so one promising way to induce the effect in neurologically intact observers is to apply transcranial magnetic stimulation (TMS) to the visual cortex. Here, we used a recently-developed criterion-free method to conclusively rule out an important alternative interpretation of TMS-induced performance without awareness: that TMS-induced blindsight may be just due to conservative reporting biases for conscious perception. Critically, using this criterion-free paradigm we have previously shown that introspective judgments were optimal even under visual masking. However, here under TMS, observers were suboptimal, as if they were metacognitively blind to the visual disturbances caused by TMS. We argue that metacognitive judgments depend on observers’ internal statistical models of their own perceptual systems, and introspective suboptimality arises when external perturbations abruptly make those models invalid -- a phenomenon that may also be happening in actual blindsight.

Aim  We sought to characterize visual motion processing in children with cerebral visual impairment (CVI) due to periventricular white matter damage caused by either hydrocephalus (eight individuals) or periventricular leukomalacia (PVL) associated with prematurity (11 individuals). Method  Using steady‐state visually evoked potentials (ssVEP), we measured cortical activity related to motion processing for two distinct types of visual stimuli: ‘local’ motion patterns thought to activate mainly primary visual cortex (V1), and ‘global’ or coherent patterns thought to activate higher cortical visual association areas (V3, V5, etc.). We studied three groups of children: (1) 19 children with CVI (mean age 9y 6mo [SD 3y 8mo]; 9 male; 10 female); (2) 40 neurologically and visually normal comparison children (mean age 9y 6mo [SD 3y 1mo]; 18 male; 22 female); and (3) because strabismus and amblyopia are common in children with CVI, a group of 41 children without neurological problems who had visual deficits due to amblyopia and/or strabismus (mean age 7y 8mo [SD 2y 8mo]; 28 male; 13 female). Results  We found that the processing of global as opposed to local motion was preferentially impaired in individuals with CVI, especially for slower target velocities (p=0.028). Interpretation  Motion processing is impaired in children with CVI. ssVEP may provide useful and objective information about the development of higher visual function in children at risk for CVI.

Perceptual rivalry-the experience of alternation between two mutually exclusive interpretations of an ambiguous image-provides powerful opportunities to study conscious awareness. It is known that individual subjects experience perceptual alternations for various types of bistable stimuli at distinct rates, and this a stable, heritable trait. Also stable and heritable is the peak frequency of induced gamma-band (30-100 Hz) oscillation of a population-level response in occipital cortex to simple visual patterns, which has been established as a neural correlate of conscious processing. Interestingly, models for rivalry alternation rate and for the frequency of population-level oscillation have both cited inhibitory connections in cortex as crucial determinants of individual differences, and yet the relationship between these two variables has not yet been investigated. Here, we used magnetoencephalography to compare differences in alternation rate for binocular and monocular types of perceptual rivalry to differences in evoked and induced gamma-band frequency of neuromagnetic brain responses to simple nonrivalrous grating stimuli. For both types of bistable images, alternation rate was inversely correlated with the peak frequency of late evoked gamma activity in primary visual cortex (200-400 ms latency). Our results advance models of inhibition that account for subtle variation in normal visual cortex, and shed light on how small differences in anatomy and physiology relate to individual cognition and performance.