Orthographic Depth

A measure of how consistently a written language maps between its spelling (graphemes) and pronunciation (phonemes). Shallow or transparent orthographies like Spanish, Finnish, and Italian have highly consistent letter-to-sound correspondences, while deep or opaque orthographies like English and French have many irregular and inconsistent mappings. Orthographic depth significantly affects how dyslexia manifests across languages: in shallow orthographies, reading speed and fluency are the primary indicators, while in deep orthographies, reading accuracy and spelling errors predominate. This concept is important for accessibility because it means that reading support tools, dyslexia screeners, and text-to-speech systems must be calibrated differently for different languages.