information in working memory. Perry et al.^23 suggest a hierarchical view, compatible with
other evidence,^24 such that right inferior lateral frontal areas are important for maintenance of
tonal information, whereas dorsolateral frontal areas are required for higher-level functions
such as monitoring the contents of working memory. This conclusion would be in accord with
the lesion study described earlier,^18 as well as with PET studies^25 that also indicated increased
activity in the right frontal cortex during pitch judgements on speech syllables.
Several other imaging studies over the past few years have supported the idea that the
right secondary auditory cortex may be particularly important in processing tonal patterns
(but see Chapter 10, this volume, for evidence that the story is more complicated).The
results of Démonet et al.26,27are relevant, since tone judgement tasks were used, in which
subjects were required to detect pitch changes of tones within a sequence, and the difference
in activity pattern between the tonal task and a language task was examined. The findings
were consistent with data presented above, implicating the right auditory cortical areas in
tonal processes, since foci were observed in posterior right STG and middle temporal areas.
More recently, Binder et al.^28 reported whole-brain fMRI data using an active tone judge-
ment task. This task, which required subjects to discriminate two pitches during a series of
tones (which ranged from 3 to 7 tones in length) and then to make a judgement pertaining
to the entire series of tones, emphasized not only pitch perception but also maintenance of
simple pitch information in working memory. When this task was compared to an active
task involving semantic categorization of words, stronger activation associated with the tone
task was observed in the posterior STG bilaterally, the supramarginal region bilaterally (but
much more on the right), the right posterior middle temporal gyrus, premotor cortex bilat-
erally (also much more on the right), and right superior parietal cortex.^28 These right
temporoparietal foci are in agreement with the right posterior STG, middle temporal, and
inferior parietal foci reported by Démonet in their tone-speech comparisons.26,27
A further source of relevant evidence comes from studies of musical imagery (reviewed
by Halpern, Chapter 15, this volume). Those studies, including both behavioural-lesion
experiments and functional imaging,^29 –^31 have indicated that a greater role is played by sec-
ondary auditory cortical areas on the right than on the left not only in perceptual tasks
involving judgements of real melodies, but also in imaginal tasks in which subjects are
invited to imagine a well-known tune in ‘the mind’s ear’. These studies, together with addi-
tional recent neuroimaging findings pointing in the same general direction,^32 –^34 provide
additional evidence for a special role of several right-hemispheric cortical regions in vari-
ous aspects of tonal pattern processing.
Hemispheric differences in spectral processing
Much of the evidence presented above converges towards the conclusion that hemispheric
specialization exists in the processing of pitch information, with right auditory cortical areas
playing a more prominent role than left. Moving beyond the mere fact that differences do
exist, it is critical to pose the question of why such lateralization might have evolved. One
classic way of thinking about hemispheric differences, favoured, for example, by investiga-
tors such as Teuber or Sperry, is in terms of complementary functional specialization—that
is, that hemispheric processing advantages emerge because they confer some advantage
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