Regional cerebral blood flow was measured with positron emission tomography (PET) in 10 healthy male volunteers. They heard two binaurally delivered concurrent stories, one spoken by a male voice and the other by a female voice. A third story was presented at the same time as a text running on a screen. The subjects were instructed to attend silently to one of the stories at a time. In an additional resting condition, no stories were delivered. PET data showed that in comparison with the reading condition, the brain activity in the speech-listening conditions was enhanced bilaterally in the anterior superior temporal sulcus including cortical areas that have been reported to be specifically sensitive to human voice. Previous studies on attention to non-linguistic sounds and visual objects, in turn, showed prefrontal activations that are presumably related to attentional control functions. However, comparisons of the present speech-listening and reading conditions with each other or with the resting condition indicated no prefrontal activity, except for an activation in the inferior frontal cortex that was presumably associated with semantic and syntactic processing of the attended story. Thus, speech listening, as well as reading, even in a distracting environment appears to depend less on the prefrontal control functions than do other types of attention-demanding tasks, probably because selective attention to speech and written text are over-learned actions rehearsed daily.
Adult Attention