Two hearing children of deaf parents (initially 3;9 and 1;8) had been cared for almost exclusively by their mother, who did not speak or sign to them. Though the older child had heard language from TV and briefly at nursery school, his speech was below age level and structurally idiosyncratic. Intervention led to improvement in his expressive abilities, and by 4;2 the deviant utterance patterns had disappeared. In later years, his spontaneous speech and school performance were normal, though language testing revealed some weak areas. The younger child initially used no speech, but acquired language normally after intervention, with his brother as model. Implications for understanding the role of linguistic input in language development are discussed.

Two experiments focus on Thai tone perception by native speakers of tone languages (Thai, Cantonese, and Mandarin), a pitch–accent (Swedish), and a nontonal (English) language. In Experiment 1, there was better auditory-only and auditory–visual discrimination by tone and pitch–accent language speakers than by nontone language speakers. Conversely and counterintuitively, there was better visual-only discrimination by nontone language speakers than tone and pitch–accent language speakers. Nevertheless, visual augmentation of auditory tone perception in noise was evident for all five language groups. In Experiment 2, involving discrimination in three fundamental frequency equivalent auditory contexts, tone and pitch–accent language participants showed equivalent discrimination for normal Thai speech, filtered speech, and violin sounds. In contrast, nontone language listeners had significantly better discrimination for violin sounds than filtered speech and in turn speech. Together the results show that tone perception is determined by both auditory and visual information, by acoustic and linguistic contexts, and by universal and experiential factors.