Impairments of multisensory integration and cross-sensory learning as pathways to dyslexia.

Two sensory systems are intrinsic to learning to read. Written words enter the brain through the visual system and associated sounds through the auditory system. The task before the beginning reader is quite basic. She must learn correspondences between orthographic tokens and phonemic utterances, and she must do this to the point that there is seamless automatic 'connection' between these sensorially distinct units of language. It is self-evident then that learning to read requires formation of cross-sensory associations to the point that deeply encoded multisensory representations are attained. While the majority of individuals manage this task to a high degree of expertise, some struggle to attain even rudimentary capabilities. Why do dyslexic individuals, who learn well in myriad other domains, fail at this particular task? Here, we examine the literature as it pertains to multisensory processing in dyslexia. We find substantial support for multisensory deficits in dyslexia, and make the case that to fully understand its neurological basis, it will be necessary to thoroughly probe the integrity of auditory-visual integration mechanisms.