Crossmodal integration is a critical component of successful reading, and yet it has been less studied than reading’s unimodal subskills. Proficiency with the sounds of a language (i.e., the phonemes) and with the visual representations of these sounds (graphemes) are both important and necessary precursors for reading, but the formation of a stable integrated representation that combines and links these aspects, and subsequent fluent and automatic access to this crossmodal representation, is unique to reading and is required for its success. Indeed, individuals with specific difficulties in reading, as in dyslexia, demonstrate impairments not only in phonology and orthography but also in integration. Impairments in only crossmodal integration could result in disordered reading via disrupted formation of or access to phoneme–grapheme associations. Alternately, the phonological deficits noted in many individuals with dyslexia may lead to reading difficulties via issues with integration: children who cannot consistently identify and manipulate the sounds of their language will also have trouble matching these sounds to their visual representations, resulting in the manifested deficiencies. We here discuss the importance of crossmodal integration in reading, both generally and as a potential specific causal deficit in the case of dyslexia. We examine the behavioral, functional, and structural neural evidence for a crossmodal, as compared to unimodal, processing issue in individuals with dyslexia in comparison to typically developing controls. We then present an initial review of work using crossmodal- versus unimodal-based reading interventions and training programs aimed at the amelioration of reading difficulties. Finally, we present some remaining questions reflecting potential areas for future research into this topic.
