PURE ALEXIA AND THE VIEWING POSITION EFFECT IN PRINTED WORDS

In the present article, we investigated the reading ability of CP, a p ure alexic patient, using an experimental paradigm that is known to el icit the viewing position effect in normal readers. The viewing positi on effect consists of a systematic variation of word recognition perfo rmance as a function of fixation location within a word: Word recognit ion is best when the eyes fixate slightly left from the word centre an d 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 showed that, like normal readers, CP was able to process all letters of a word in one fixation. However, in contrast to normal readers, reading performance was optimal when CP was fixating the rig ht 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, i ndependent of visual field presentation. A similar pattern of performa nce was obtained with normal readers under experimental conditions in which lexical knowledge was of restricted use. We suggest that CP's re ading impairment stems from a dysfunction in the coupling between inco ming visual information and stored lexical information. This dysfuncti on is thought to uncover a prelexical level of word processing, where letter information is weighted differently as a function of letter pos ition in a word-centred space.