A Visual Disorder Producing Highly Selective Deletion of Recurring Letters

A case of unusually selective deletion of recurring letters is described. The disorder was primarily visual, spelling being unaffected. There was no evidence of neglect. Reading was fluent and rapid (not letter-by-letter), though words often appeared as a series of resolving fragments. Selective deletions were entirely confined to adjacent letters, excluding explanation in terms of repetition blindness (Kaniwisher, 1991). Mixing case and font, or increasing inter-letter distance, did not alter rate of recurring letter deletion, provided the task required some form of perceptual grouping. The final 2 experiments establish the pre-lexical nature of the deficit; they show deletion of recurring symbols, for example, when copying Navon-style global forms constructed from same or different Greek letters. This visual deficit is explained using the neural network model developed by Rolls and Deco (2002).