Cortical categorization failure in 2-month-old infants at risk for dyslexia.

Cortical auditory categorization was assessed in 2-month-old infants at genetic risk for dyslexia and controls. Manipulated /bAk/ and /dAk/ speech stimuli were used as frequently presented standards. The neuroelectric brain responses of the control infants were highly sensitive to the phoneme boundary that separated these stimuli, but the infants at risk showed no signs of cortical categorical perception. Cortical sources of the responses were predominantly found in the left hemisphere for the control infants, but mainly in the right hemisphere for the infants at risk. The results demonstrate that impaired categorical perception in dyslexia is already present in infants at risk for the disorder.