VISUAL AND LANGUAGE PROCESSING DISORDERS ARE CONCURRENT IN DYSLEXIA AND CONTINUE INTO ADULTHOOD

A recent study by Slaghuis, Lovegrove and Davidson (1994) found that v isual and language processing differences were concurrent in a group o f preadolescent dyslexics. In the present study, two experiments are r eported that investigate the concurrence and continuity of visual and language processing differences in groups of young and adult dyslexics on a measure of visual processing and a measure of phonological codin g. The visual processing task in the present experiments was a measure of Ternus apparent movement which was used as an index of the duratio n of visible persistence. Ternus apparent movement is multistable and provides two mutually exclusive and easily distinguishable percepts fo r the observer, referred to as 'element' and 'group' movement, that ar e highly dependent on the temporal interval between frame 1 and frame 2 of the display. The language processing task in the present experime nts was a test of phonological coding measured using a non-word test o f 100 orthographically legal non-words. The results of the first exper iment showed that in comparison to normal readers the young dyslexic p articipants showed a significant reduction in Ternus 'group movement' and a significant reduction in the pronunciation of non-words. In a se cond experiment, Ternus apparent movement and performance on the non-w ord test was measured in groups of adult dyslexic and normal readers i n order to investigate whether the visual and language processing diff erences found in young dyslexics were also present in adult dyslexics. The results showed that adult dyslexics also have a significant reduc tion in Ternus 'group movement' and a significant reduction in the abi lity to pronounce nonwords similar to that found in the young dyslexic group in Experiment 1. The significant reduction in Ternus 'group mov ement' in dyslexic participants was explained in terms of an increase in the duration of Visible persistence acid was shown to be consistent with evidence for a transient system disorder. The combined results s how that visual and language processing differences are concurrent in dyslexia and continue into adulthood.