PURE ALEXIA AND THE VIEWING POSITION EFFECT IN PRINTED WORDS

Abstract

In the present article, we investigated the reading ability of CP, a pure alexic patient, using an experimental paradigm that is known to elicit the viewing position effect in norm al readers. The viewing position effect consists of a systematic variation of word recognition performance as a function of fixation location w ithin a word: Word recognition is best when the eyes fixate slightly left from the word centre and decreases when the eyes deviate from this optimal viewing position. A mathematical model (Nazir, O'Regan, & Jacobs, 1991), which provides a good description and quantification of the prototypical shape of the viewing position effect, served to interpret CP's reading performance. The results show ed that, like normal readers, CP was able to process all letters of a w ord in one fixation. However, in contrast to normal readers, reading performance was optimal when CP w as fixating the right half of the word. This somewhat abnormal pattern of performance was due to (1) poor perceptual processing in the right visual field, and (2) poor processing of letters situated towards the end of the word, independent of visual field presentation. A similar pattern of perform ance w as obtained with normal readers under experimental conditions in which lexical know ledge was of restricted use. We suggest that CP's reading impairment stems from a dysfunction in the coupling between incoming visual information and stored lexical information. This dysfunction is thought to uncover a prelexical level of word processing, where letter information is weighted differently as a function of letter position in a word-centred space.

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