The developmental relationship between linguistic semantic processing and non-linguistic semantic processing (interpreting pictures) is investigated in a longitudinal neuroimaging study of two deaf individuals who did not begin acquiring their first language until the age of 14. 1-2 years after they began learning language, the two case studies performed a picture-sign priming task. Magnetoencephalography was localized to the cortical surface, showing that picture processing was initially bilateral or focused in the canonical left hemisphere language network, while single sign processing was initially focused in the right hemisphere. After 15 months of additional language experience, the neural responses to both pictures and single signs reversed in lateralization, becoming more similar to those observed in a control group of native signers. The results shed new light on the interdependence between linguistic and non-linguistic semantics in cognitive development, as well as the neural underpinnings of semantic processing.