Asynchrony of visual-orthographic and auditory-phonological word recognition processes: An underlying factor in dyslexia

This study investigated whether asynchrony of speed of processing (SOP) between visual-orthographic and auditory-phonological modalities can account for word recognition deficits among dyslexic readers. SOP among elementary school dyslexic readers was compared to that of chronologically age-matched normal readers. SOP was assessed using nonlinguistic and linguistic auditory and visual low-level tasks and higher-level orthographic and phonological tasks. Behavioral and electrophysiological (ERP) measures of SOP were obtained. Data indicated that dyslexic readers were significantly slower than control readers in most of the experimental tasks. Moreover, dyslexies revealed a systematic SOP gap between the auditory-phonological and the visual-orthographic modalities. This gap was found in both P200 and P300 latencies, and explained most of the variance in word recognition. A theory is proposed suggesting that asynchrony between the processing rates of the visual and the auditory modalities may be an underlying cause of dyslexia.