Phonetic speech perception deficits in dyslexia.

Adult developmental dyslexics showed deficits in the identification of the vowels of English when the sole acoustic cues were steady-state formant frequency patterns. Deficits in the identification of place of articulation of the English stop-consonants [b], [d] and [g] in syllable-initial position were also observed. The average consonantal error rate was 22%. These error rates are significantly different from those of nondyslexic control groups (p less than .01). No single deficit characterized the entire group of dyslexic subjects. The pattern of errors with respect to place of articulation also varied for different groups of subjects. Three dyslexics have high vowel error rates and low consonantal error rates. The data are consistent with the premise that dyslexic subjects may have different perceptual deficits rather than a general auditory deficit involving the rate at which they can process perceptual information. The clinical histories of the present subjects suggest genetic transmission of these speech perception deficits. The presence of genetic variation in the biological substrate relevant to the perception of human speech should be further explored.