auditory stimulus equipment for EEG recordings - follow up (Tobias Overath )


Subject: auditory stimulus equipment for EEG recordings - follow up
From:    Tobias Overath  <otobias@xxxxxxxx>
Date:    Wed, 16 Apr 2014 10:39:28 +0200
List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>

--Apple-Mail=_24B6D83B-1402-48F6-A798-ED94CCEEA7C1 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=windows-1252 Dear All, I have received a few =91private=92 replies to my post last month asking = about pros and cons of auditory stimulus equipment for EEG recordings = (http://www.auditory.org/mhonarc/2014/msg00184.html); I have also had a = couple queries whether I would mind sharing these. So here is a synopsis = of the replies that I have gotten, which may be informative for some. = Please jump in and correct if any of this is inaccurate or incomplete. Previously, I had heard from someone who had done a comparison of insert = earphones (3MTM E-A-RTONE), headphones (Beyerdynamic TD-48), and a = loudspeaker, using a melon; all three ways of stimulus delivery produced = some sort of artifact (and in a way the insert earphones produced larger = artifacts than headphones, though that might have been due to the = placement of the transducers). But a melon is apparently not such a good = model for EEG; a conductive medium, e.g. a bucket of salt water, would = perhaps be better, lest the leads end up acting like antennae. Again, if = anyone has done or is aware of a comprehensive comparison, I for one = would be very interested (and I know others would be too). For looking at brainstem or oscillatory activity in particular it seems = like insert earphones, e.g. the Etymotics (e.g. = https://www.etymotic.com/pro/er3a.aspx), are the way to go, since these = arguably introduce the smallest amount of acoustic signal correlated = corruption by virtue of the last part being a plastic tube (i.e. there = is no transducer near the head or ear). For brainstem recordings in = particular, higher frequencies are of interest that might overlap with = those of the acoustic stimuli - this is not so much an issue when = looking at low-frequency ERPs - and it is therefore vital to exclude = these from interfering with the recording. However, since in those insert earphones the last part is a tube, the = signal fidelity drops for frequencies > 4 kHz. Another potential = disadvantage of insert earphones is that one needs to take great care = fitting them into the ear canal to a) achieve a good seal and b) avoid = one of them coming out over the course of the experiment, which = introduces a lateralized sound percept. Similarly, apparently some EEG = caps have relatively small cuts to fit the ears through, and fitting = insert earphones might be difficult in this case. Headphones have comparatively better overall sound quality and are = widely used. One thing to look out for is to use supra-aural instead of = circumaural ear cushions, and secondly that the bracket/bow must not = touch any leads. They might also start to feel uncomfortable for long = experiments. It seems no-one has used the Sensimetrics S14 earphones in an EEG set = up. Hope this was helpful to some, Tobias -- Tobias Overath, PhD Duke Institute for Brain Sciences P.O. Box 91003 Duke University Durham, NC 27708 U.S.A. --Apple-Mail=_24B6D83B-1402-48F6-A798-ED94CCEEA7C1 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=windows-1252 <html><head><meta http-equiv=3D"Content-Type" content=3D"text/html = charset=3Dwindows-1252"> <meta http-equiv=3D"Content-Type" content=3D"text/html; = charset=3DWindows-1252"></head><body style=3D"word-wrap: break-word; = -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">Dear = All,<div><br></div><div>I have received a few =91private=92 replies to = my post last month asking about pros and cons of auditory stimulus = equipment for EEG recordings (<a = href=3D"http://www.auditory.org/mhonarc/2014/msg00184.html">http://www.aud= itory.org/mhonarc/2014/msg00184.html</a>); I have also had a couple = queries whether I would mind sharing these. So here is a synopsis of the = replies that I have gotten, which may be informative for some. Please = jump in and correct if any of this is inaccurate or = incomplete.</div><div><br></div><div>Previously, I had heard from = someone who had done a comparison of insert earphones (3MTM E-A-RTONE), = headphones (Beyerdynamic TD-48), and a loudspeaker, using a melon; all = three ways of stimulus delivery produced some sort of artifact (and in a = way the insert earphones produced larger artifacts than headphones, = though that might have been due to the placement of the transducers). = But a melon is apparently not such a good model for EEG; a conductive = medium, e.g. a bucket of salt water, would perhaps be better, lest the = leads end up acting like antennae. Again, if anyone has done or is aware = of a comprehensive comparison, I for one would be very interested (and I = know others would be too).</div><div><br></div><div>For looking at = brainstem or oscillatory activity in particular it seems like insert = earphones, e.g. the Etymotics (e.g. <a = href=3D"https://www.etymotic.com/pro/er3a.aspx">https://www.etymotic.com/p= ro/er3a.aspx</a>), are the way to go, since these arguably introduce the = smallest amount of acoustic signal correlated corruption by virtue of = the last part being a plastic tube (i.e. there is no transducer near the = head or ear). For brainstem recordings in particular, higher frequencies = are of interest that might overlap with those of the acoustic stimuli - = this is not so much an issue when looking at low-frequency ERPs - and it = is therefore vital to exclude these from interfering with the = recording.</div><div>However, since in those insert earphones the last = part is a tube, the signal fidelity drops for frequencies &gt; 4 kHz. = Another potential disadvantage of insert earphones is that one needs to = take great care fitting them into the ear canal to a) achieve a good = seal and b) avoid one of them coming out over the course of the = experiment, which introduces a lateralized sound percept. Similarly, = apparently some EEG caps have relatively small cuts to fit the ears = through, and fitting insert earphones might be difficult in this = case.</div><div><br></div><div>Headphones have comparatively better = overall sound quality and are widely used. One thing to look out for is = to use supra-aural instead of circumaural ear cushions, and secondly = that the bracket/bow must not touch any leads. They might also start to = feel uncomfortable for long experiments.</div><div><br></div><div>It = seems no-one has used the Sensimetrics S14 earphones in an EEG set = up.</div><div><br></div><div>Hope this was helpful to = some,</div><div><br></div><div>Tobias</div><div><br></div><div><div = style=3D"orphans: 2; widows: 2; color: rgb(128, 128, 128);">--</div><div = style=3D"orphans: 2; widows: 2; color: rgb(128, 128, 128);">Tobias = Overath, PhD</div><div style=3D"orphans: 2; widows: 2; color: rgb(128, = 128, 128);">Duke Institute for Brain Sciences</div><div style=3D"orphans: = 2; widows: 2; color: rgb(128, 128, 128);">P.O. Box 91003</div><div = style=3D"orphans: 2; widows: 2; color: rgb(128, 128, 128);">Duke = University</div><div style=3D"orphans: 2; widows: 2; color: rgb(128, = 128, 128);">Durham, NC 27708</div><div style=3D"orphans: 2; widows: 2; = color: rgb(128, 128, 128);">U.S.A.</div><div><br></div> </div></body></html>= --Apple-Mail=_24B6D83B-1402-48F6-A798-ED94CCEEA7C1--


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