Abstract
“Blindsight” is a term first coined by Weiskrantz et al. in 1974 to describe residual visual performance in the cortically blind. It has been postulated that blindsight could be due to the retinotectal pathway projecting information past V1 to later cortical structures. Our interest was in whether the pathways responsible for blindsight could also support enumeration. We tested a 53-year-old male, C.H., who had suffered a medial right occipital lobe stroke seven months previous. The stroke resulted in an upper left homonymous quadrantanopia. In order to determine whether there were any residual abilities in the blind field, we first tested basic detection and discrimination skills. C.H. was able to determine whether or not a 7° X 7° visual angle object was presented in his blind field with near perfect accuracy though his accuracy was only 90% for smaller (4.6° X 2.2°) figures. C.H. also discriminated between large X′s and O′s and horizontal and vertical bars with good accuracy when the figures were large (78% for X vs. O and 73% for horizontal vs. vertical bars). Throughout these tests C.H. staunchly maintained that he could not see the stimuli and that he was only guessing. Because it was clear that C.H. had some residual ability in his blind field, we tested his enumeration. The enumeration task involved 1-3 items. These items were 1.5° X 1.5° black diamonds, 0-2 in his blind field and 1-3 in his non-blind field. Across all conditions, C.H. was able to use the information in his blind field and identify the total number of items presented at levels of performance that were well above chance. Because C.H. appears to use blind field information to enumerate, we postulate that enumeration ability may be mediated by the same structures that support blindsight.