As discussed earlier in this paper, the perceptual identity of a sound depends on both a
sound’s temporal structure as well as its spectral content. For example, periodic modula-
tions of a sound’s amplitude evoke a pitch percept. Taken together, the results from the
numerous studies on the functional organization of the human auditory cortex suggest a
different functional hemispheric asymmetry in the processing of spectral and temporal
information. Frequency (i.e. spectral information) may be processed in HG of the right
hemisphere, while temporal information may be processed in the left hemisphere. Not all
data, however, is consistent with this idea. Using MEG, Langner et al.^51 found that perio-
dicity pitch and frequency are arranged orthogonally in the human auditory cortex, with
no differences observed according to hemisphere.
The asymmetry observed in the tonotopic organization of the right and left auditory
cortices could underlie hemispheric specialization and could account for a fair amount of
behavioural data obtained in studies on human auditory function. Robin et al.^52 found that
left temporoparietal lesions impair the perception of temporal but not spectral auditory
information; lesions in homologous regions of the right hemisphere were found to have
the opposite effect. The lesions referred to in their study affected only the associative audi-
tory areas, but such lesions could also disconnect the primary cortex from the rest of the
brain.53,54Taken together with these findings, the present study’s results suggest that the
frequency analysis of sounds corresponds to the neural sharpening for neurons tuned to
frequency. This mechanism could be conferred on the right auditory cortex, which plays an
important role in the processing of pitch.26,55Auditory neurons in the left hemisphere,
on the other hand, have been shown to be more selective for temporal pattern^50 than for
spectral pattern. Such data are consistent with the results from studies with language-
disordered subjects who have left-hemispheric lesions, suggesting that many of these
patients are also impaired in auditory temporal perception.^56
In conclusion, these results suggest that the processing of spectral information is carried
out primarily in the right hemisphere, and the processing of the temporal aspects of audi-
tory stimuli in the left auditory cortex.^50 Future research in this direction could not only
provide insight into the cortical processes underlying speech and music perception, but
may also help us better understand the psychoacoustic sequelae of cortical lesions.
Acknowledgements
The authors are grateful to Drs B. Devaux (Ste. Anne Hospital, Paris), A. Musolino (Clinica
Neurochirurgica, Messina, Italy), and J.M. Scarabin (Pontchaillou Hospital, Rennes) for
their collaboration.
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2.Shamma, S. A.(1985) Speech processing in the auditory system II: lateral inhibition and the
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