Variability of residual vision in hemianopic subjects

Using stabilized visual field mapping techniques, seven hemianopic subjects were extensively investigated for residual visual abilities. Isolated isla nds of detection abilities were demonstrated by four of these subjects. Add itional abilities demonstrated within these islands included saccadic and v erbal localization, wavelength discrimination, form discrimination, and mot ion detection. These abilities were also accompanied by low-confidence rati ngs, and thus have the character of blindsight. It is noteworthy that diffe rent subjects demonstrated different abilities at different visual field lo cations, underscoring the between and within subject variability often obse rved with blindsight. Furthermore, magnetic resonance images obtained for e ach subject demonstrated variable sparing of occipital cortex. Such cortica l sparing, in conjunction with the behavioral variability, supports the not ion that some instances of blindsight are mediated by remnants of the prima ry visual pathway.