Two left-hemisphere mechanisms in speech perception

Right-ear advantages of different magnitudes occur systematically in dichotic listening for different phoneme classes and for certain phonemes according to their syllabic position. Such differences cannot be accounted for in terms of a single mechanism unique to the left hemisphere. Instead, at least two mechanisms are needed. One such device appears to be involved in the auditory analysis of transitions and other aspects of the speech signal. This device appears to be engaged for speech and nonspeech sounds alike. The other mechanism, the more accustomed “speech processor”, appears to make all phonetic decisions in identifying the stimulus.