Task-dependent modulation of neglect dyslexia? Novel evidence from the viewing position effect.

Spatial neglect may involve neglect dyslexia resulting in a failure to identify words or parts of words in the contralesional hemispace. The present study explored a well-documented dissociation in neglect dyslexics' word processing, i.e. impaired reading aloud in the presence of good lexical decision performance for the same stimuli. To investigate whether this dissociation is also reflected in the visuo-spatial characteristics of word processing, a well-established paradigm of word processing in normal readers (technique of variable viewing positions, [Nazir, T., Heller, D., Sussmann, C., 1992. Letter visibility and word recognition: The optimal viewing position in printed words. Perception and Psychophysics, 52, 315-328]) was combined with a word naming and a lexical decision task. Compared to previous studies of neglect dyslexia, the present study additionally entailed tachistoscopical displays of word stimuli in different viewing positions. The word stimuli varied orthogonally along the two linguistic dimensions of word frequency (lexical manipulation) and syllable number (sublexical manipulation). Participants were sixteen patients with left-sided visual neglect and an age-matched control group. We expected the dissociation in neglect dyslexia to be reflected in task-specific effects in naming and lexical decision. This was partly confirmed by an interaction of task demands with viewing-position-specific results. Interestingly these results pointed to a task-dependency in word processing not only in neglect patients but also in normal readers, when equal error rates were experimentally obtained between control and neglect participants. Together with the finding of a task-specific effect of syllable number in the neglect group, the present results suggest that task demands modulate the degree of neglect dyslexia from early stages of visual word processing.