Children whose reading and spelling problems get classified as dyslexia fail to note a critical rhythmic beat in spoken words, a new study suggests. This sound cue, which lasts for one-tenth to one-fifth of a second, marks the transition from a consonant sound to a speech segment beginning with a vowel.
Such rhythmic neglect may make it difficult to sound out words when reading, say psychologist Usha Goswami of University College London and her colleagues. In particular, problems may arise for words that are similar or that rhyme, such as seat, sweet, and street.
The scientists first studied 24 children diagnosed with dyslexia and 49 others reading at an age-appropriate grade level. Kids in both groups were 9 years old. Only those with dyslexia had difficulty discerning the beat in continuous sounds containing sudden rises and falls in loudness, as in such speech transitions as sw–eet. Moreover, in a group of 11-year-olds, 14 superior readers performed much better on this task than 14 average readers, the researchers report in the August 6 Proceedings of the National Academy of Sciences.
In the London study, children with dyslexia encountered few problems in discerning extremely short sound modulations, which correspond to individual units of speech. Other researchers suspect that dyslexia involves an inability to hear the difference between these sounds, such as p versus b (SN: 3/18/00, p. 180: Good Readers May Get Perceptual Lift).