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Auditory stimulation for fMRI

I am working with the group of Erv Hafter in UC Berkeley, trying to figure
out what the state-of-the art is for auditory stimulus delivery in
functional MRI experiments. As we see it, the requirements of such a system
would be at least :

1. To provide attenuation of the scanner noise so as
        a) to defend the subject's hearing from being damaged by the
scanner noise, which can get, apparently, higher that 135dB at
3Tesla      (we intend to use 4T) and
        b) to minimize the masking of the stimuli by the scanner noise
2. Having a flat (ideally) or predictable frequency response over the
widest range of frequencies possible, or at least in the speech range
3. Having a reliable inter-aural balance, that will allow manipulations of
inter-aural parameters.
4. Being compatible with the magnetic field requirements so that as little
disruption of the MR signal will occur

The major questions are:
Air tube vs. Electrostatic/ Piezoelectric earphones.
Any one of the above - what make? Are there any good on the shelf products?

Regarding electrostatic earphones we know that the group from IHR in
Nottingham has modified a set of Senheiser earphones to the degree that (if
we correctly understand) they can be used without earplugs. There is an
extensive description of their system in http://www.ihr.mrc.ac.uk/caf/caf.shtml

There are also KOSS Earphones that are apparently MR compatible which the
group in Wisconsin helped modifying (Model 'medical ESP 900' ). The KOSS
company sales person told me that they sold about 20 of those and that some
modification was needed by the user to make it really usable in MRI
studies. He could not say what these modifications were - we would
appreciate any tip on this. It also seems that these headphones need to
used together with earplugs.

What is the experience with these systems? Are there any major solution
that we missed?

Leon Deouell


Dr. Leon Y Deouell, M.D.
Department of Psychology
4143 Tolman Hall #5050
University of California
Berkeley, CA 94720-5050

Tel: (510) 6439744
Fax:(510) 6421196
e-mail: deouell@socrates.berkeley.edu