Natural variation in both position coding and visual attention affects visual word recognition

Letter-position coding is known to be important in text processing, and may be impaired in those with reading disability. We have studied the natural variability in, and possible relation between, relative-position coding (for non-word stimuli) and visual word recognition. An unselected sample of fifty adults performed a series of tasks, including measurement of attentional dwell time, visual word recognition (assessed by a lexical decision task), coherent-motion detection, colour detection, and relative-position coding. We measured the latter with a paradigm based on the lexical decision task, but which required the subject to process the relative order of a string of novel symbols. Controlling for age, IQ, and reading ability, we found that accurate visual word recognition was best predicted by independent contributions from both the attentional-dwell-time and position- coding tasks. Previous findings were also replicated with regard to coherent-motion detection and lexical decision (Cornelissen et al, 1998 Vision Research 38 2181-2191). Subjects' performance in colour detection was uncorrelated with their performance in the attention, motion, and position tasks. Since many developmental dyslexics exhibit poor performance on dynamic visual tasks, these findings may have implications for whether reading difficulties can be caused by visual-system impairment.