A phoneme is a speech sound – the smallest contrastive sound unit in a language. When children learn their native languages, part of what they learn is to correctly perceive, produce, and combine the phonemes of their language. Though most children with autism acquire speech normally, some have difficulties with spoken language. These difficulties can range from “residual speech errors,” which are persistent mispronunciations of one or more phonemes (such as “w” for “r”) past the age of 8, to the complete absence of spoken language.
A phoneme is a cognitive construct, not a feature of the acoustic signal. Acoustically, speech is a continuous signal; however, it is perceived as consisting of a series of distinct phonemes. Though repeated examples of the same phoneme differ slightly from each other acoustically, they are still perceived as belonging to the same phonetic category.
Major classes of phonemes are vowels (such as “a” or “i”), consonants (such as “b” or “s”), and glides (such as “w”) or liquids (such as “l”). Vowels are produced with the vocal tract largely open and unobstructed. On the other hand, consonants are produced with a tight constriction or momentary closure somewhere in the vocal tract. Glides and liquids are produced with an intermediate degree of constriction. Phonemes are classified in terms of phonetic features that describe place of articulation (where in the vocal tract the phoneme is produced), manner of articulation (how it is produced), and voicing (whether the larynx is vibrating during production of the phoneme). For example, “v” is classified as a voiced labiodental fricative. “Voiced” means that the larynx is vibrating while it is produced. This is in contrast with “f,” which is unvoiced because the larynx does not vibrate during its production. Like “f,” “v” is labiodental; it is produced with a constriction between the lower lip and the upper front teeth. Finally, “v” is a fricative, which means that air passes continuously through the labiodental constriction and causes a white-noise-like sound called frication.
Each language employs a different selection, or inventory, of all possible phonemes. Some phonemes, like the “th” sound in English “thin,” are rare across languages. Other phonemes, such as “b,” are used in nearly every language. Phonemes also combine with each other in ways that are determined by each language individually. For example, in Bantu words may begin with the “ng” sound, as in the name of the Ngorongoro Crater. In English, on the other hand, “ng” is only permissible at the ends of words (e.g., “sing”); it never appears word-initially.
It is important not to confuse phonemes with letters. While phonemes can be represented by letters (as we have done in the paragraphs above), the two are not the same. In English, the letter “a” can represent many phonemes, such as the “ey” sound in “apex,” the “ae” sound in “atom,” the “ah” sound in “watt,” or the “uh” sound in “banana.” Also, different letters may represent the same phoneme in different words. For example, the sound “ah” is spelled with the letter “a” in “watt” but with the letter “o” in “stop.” In order to standardize the representation of speech sounds across languages, the International Phonetic Association (IPA) has devised an alphabet in which each phoneme is represented by a unique symbol.
References and Reading
- Chenausky, K., & Tager-Flusberg, H. (2017). Acquisition of voice onset time in toddlers at high and low risk for autism spectrum disorder. Autism Research. https://doi.org/10.1002/aur.1775.
- Constantino, J. N., Yang, D., Gray, T. L., Gross, M. M., Abbacchi, A. M., Smith, S. C., & Kuhl, P. K. (2007). Clarifying the associations between language and social development in autism: A study of non-native phoneme recognition. Journal of Autism and Developmental Disorders, 37(7), 1256–1263.CrossRefPubMedGoogle Scholar