Motion reveals spatial visual defects

The question of how we can be unaware of the deficit in our (monocular) visual field, equivalent in size to 76 Full moons, is examined. A new method of investigating the response to moving images on and near the Wind spot has been found. The image of a computer-generated line, which is made to lengthen with time and pass over the blind spot, is seen as shorter than that of a similar, parallel line which passes outside the blind spot. This perceived difference in length corresponds to the actual width of the blind spot. Our unawareness of blind spots and seotomata is often described as involving some form of ‘filling in’ process. The rapid variation in cortical receptive field site. recently found lo occur in response to stabilized images, may provide a general filling-in mechanism for the removal from perception of otherwise-distracting, stabilized image regions (such as the shadows of blood vessels and clinical scotomata).