Development of hemispheric specialization for speech perception.

When lists of word pairs were presented simultaneously in a dichotic monitoring task to three groups of right-handed subjects aged 5, 7 and 11 years, more target words were responded to, and reaction times was shorter, when these occurred in the right rather than the left ear. The magnitude of the effect did not change with age. A signal detection analysis showed that the right ear advantage was due to greater sensitivity of the right ear, rather than a response bias. Hand effects were assessed separately by using binaural stimulation in which each ear received two inputs, one in a male voice and the other in a female voice. The right hand responded to target words in one voice, and the left hand to target words in the other voice. The contribution of a right hand superiority to the ear effect was found to be minimal. The effects of language acquisition and attention strategies on the right ear advantage are discussed. It was concluded that at 5 years of age the left hemisphere is specialized for the analysis of speech signals. This produces a right ear advantage in competitive verbal listening.