The role of the SMA remains unclear, in several respects. Because of our failure to dis-
rupt imagery processing with TMS inhibition, we are not sure if a fully functioning SMA
is necessary for good performance on musical imagery tasks. The strong activation of SMA
shown by PET in both verbal and nonverbal auditory imagery tasks suggests that ‘internal
humming’may at least be helpful to maintain an auditory image over time.
This latter point can be subjected to test by devising auditory imagery tasks in which
internal humming would not be helpful or even possible to support the task. One domain
to investigate would be imagery for environmental sounds. Intons-Peterson^27 has shown
that people can generate images of everything from volcanoes erupting to wind chimes tink-
ling, and make mental comparisons on subjective loudness of these sounds. As people
cannot possibly produce most of these sounds, it would be useful to find a task that shows
activation in secondary auditory areas (which we can, by now, use as a tentative correlate
of the subjective state of auditory imagery) and see if SMA is also activated.
An alternative domain to explore might be that of timbre. Crowder^28 demonstrated in
several behavioural paradigms that people asked to imagine timbres of different instru-
ments can do so. He gave people a sine wave of a particular pitch and asked them to ima-
gine it in an instrument timbre. A second tone was then presented in an actual timbre at the
same or a different pitch and subjects had to say if the pitch was the same or different as
the first note. People were slower to confirm that two pitches were the same if the imagined
and perceived timbres did not match. As people cannot produce the sounds of guitars and
clarinets, SMA support should not be necessary if it is providing a motor rehearsal pro-
gram. Timbre imagery tasks would also have the advantage of providing us a lateralization
hypothesis, as Samson and Zatorre^11 showed the importance of the right temporal lobe in
timbre tasks. Thus brain imaging studies using either PET or functional magnetic reson-
ance imaging in these domains should help us clarify the role of the SMA in auditory
imagery tasks.
Acknowledgements
I thank the National Science Foundation and the McDonnell-Pew Program in Cognitive
Neuroscience for support of this research.
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