The interface between the perception and production of speech

Abstract

Four positron emission tomography studies were reanalyzed to identify anatomically separable, functional subsystems associated with speech perception, speech production, hearing complex, nonspeech sounds, and verbal semantic category verbal fluency. The results from a total of 26, right-handed, male volunteers were included. The results indicated two separate caudal (posterior) ‘‘streams’’ of auditory processing. One, directed along the supratemporal cortical plane, responded to both nonspeech and speech sounds, including the sound of the speaker’s own voice. Activity in response to perception merged at the temporo-parietal junction with a region where activity was linked to speech production. In contrast, the left superior temporal sulcus below (ventrolateral to) the caudal supratemporal plane responded only to an external source of verbal stimuli: but, in addition, it was activated by the recall of lists of words during verbal fluency. The results are compatible with a hypothesis that the caudal superior temporal cortex is specialized for the mimicry of sounds, including repetition, the role of the caudal left superior temporal sulcus being to transiently represent verbal sequences, whether heard or internally generated and rehearsed. These processes are central to the perception, rehearsal (both covert and overt), and eventual acquisition of long-term lexical memories of novel words.