Magnetically induced phosphenes in sighted, blind and blindsighted observers

Direct stimulation of visual cortex can produce illusory flashes of light, called phosphenes. Here we describe the spatial and motion properties of phosphenes produced by transcranial magnetic stimulation in normal subjects and in two subjects with peripheral or cortical blindness. The totally retinally blind subject experienced normal phosphenes, apart from their concentration in the centre of the visual field, whereas the hemianopic subject, lacking area V1, did not experience phosphenes when his surviving extrastriate visual areas were stimulated. In the absence of V1, magnetically induced activity was unable to generate a conscious visual percept in the field defect.