Examining the validity of IQ-discrepancy definition in dyslexia: what do temporal processes tell us?

Abstract

This study attempted to examine the validity of the IQ-discrepancy based definition of dyslexia from the point of view of temporal processes and reading mechanisms, an area being overlooked in the literature. One-hundred-and-five English speaking undergraduates, divided into “high IQ” and “average IQ” groups, were compared on their visual, auditory temporal and reading processes. Results indicated that “high IQ” and “average IQ” readers did not differ significantly in reading, spelling and overall temporal processing ability, even though “high IQ” group had better temporal resolution in BLAN12 (visible persistence at 12 c/deg) and AGAP15 (auditory gap detection at 15 ms). Auditory temporal order judgment and the transient visual measures significantly predicted reading and spelling independent of IQ. The temporal measures were minimally predictive of IQ, suggesting that IQ is multi-dimensional and has a negligible reciprocal interaction with temporal resolution mechanisms. The temporal and the literacy measures were not effective discriminants for individual’s intellectual capacity. The findings questioned the validity of the IQ-discrepancy definition of dyslexia within the domain of temporal processing. However, the restricted use of nonverbal IQ and proficient readers made the generalisation of the results to the verification of the IQ-discrepancy definition difficult.