The role of spatial redundancy in grapheme recognition: perception or inference?

The question under investigation is whether spatial redundancy operates by restricting the number of valid alternatives at each serial position or whether it serves a perceptual function by keeping visually confusable graphemes from appearing in the same array and/or maximizing the distance between such graphemes when they do occur in the same array. The first experiment used the same-different task to establish a confusion matrix for 12 non-linguistic symbols. The spatial relation between the members of two pairs of confusable symbols was manipulated in a second experiment, which had subjects look for the presence or absence of a predetermined target symbol in single six-symbol linear arrays. Facilitation was found to be dependent upon the perceptual consequences of serial position constraint rather than upon the constraint per se. The constraint was most effective when it served to prevent members of visually confusable pairs from occurring in the same array. Since spatial redundancy may operate at the feature extraction stage by minimizing competition for the same sets of feature detectors and since words are likely to be high in spatial redundancy, the possibility is raised that part of the word superiority effect may be due to visual factors rather than to linguistic context.