Subject: MEG headphones From: Christian Kaernbach <chris(at)psychologie.uni-leipzig.de> Date: Mon, 7 Jun 1999 11:08:19 +0200Dear List, I got some responses on my query concerning piezo headphones for MEG studies. I submit a first summary to the list. This mail will also clarify my needs (I suppose I was not too explicit in my first mail). Some contributors (Didier A Depireux, Biao Tian) doubted my statement > Usual sound application is via tubes from speakers outside of the > magneto-shielding booth, with really bad sound transmission values. Especially tubes by Etymotic Research have been recommended (Didier A Depireux, Jont Allen, http://www.etymotic.com/html/index.html ). I should have stated that what I need is _really good_ transmission values: A factor of 100 between low and high cutoff (e.g. 120 to 12,000 Hz). The tubes I have seen transmit 500-4,000 Hz. This can be improved, but is it realistic to think of tubes that transmit 120-12,000 Hz? Some contributors mailed info on headphones used in fMRI studies: Robert J. Zatorre pointed to phones by Koss (http://www.koss.com but I could not find the nonferromagnetic headphone on their web-site yet, mainly because they sell so many products; waiting for e-mail feedback from Adam Miklas, Koss corporation, amiklas(at)koss.com 414-967-1575.) These headphones cost around $1K U.S. Alan R. Palmer (Alan(at)ihr.mrc.ac.uk) transmitted a 8-page instruction of how to modify sennheiser HE60 electrostatic headphones so that they can be used in MRI environment. This goes beyond my technical capabilities, but it might be of interest to those with sufficient technical skills. My main problem is that I am not sure about the exact requirements for MEG studies and how they differ from fMRI studies. I contacted MEG people and they told me that the constraints are much more strict for MEG than for fMRI. With fMRI, high magnetic fields are applied and these should not be disturbed by the headphones. With MEG, the best precondition is the absence of any kind of magnetic field. I was told that nonferromagnetic EEG equipment that works fine for fMRI produces strong artifacts if used in the MEG booth. On the plus side, one would not need the active noise reduction that comes with some fMRI headphones. I would have highly welcomed any mail pointing to someone actually using headphones in MEG studies but it seems this is not common practice. May be this is because it is impossible... (hoping this is not true) Best, Christian