<div dir="ltr">hello EEG community,<div><br></div><div>We have a rather peculiar problem that we're hoping to get some input on.</div><div><br></div><div>In reviewing some existing 64-channel recordings, we noticed that some records show near-identical signals across al channels, with median channel-by-channel correlations of >0.99. This suggests some kind of electrical shorting, somewhere in the cap-cable-amplifier-montage-recording-exporting chain.</div><div><br></div><div>The problem appears to be infrequent (most records have more acceptable R values of 0.6-0.9), but common enough that we'll need to review several hundred records.</div><div><br></div><div>We haven't been able to identify the cause of the problem yet, and it affects ongoing data collection.</div><div><br></div><div>Some details:</div><div><br></div><div>- we use Grass AURA amplifiers and TWin software with the Easycap system</div><div>- the problem has been observed with different amplifiers, different caps, different pcs, and at different sites</div><div>- the problem is there regardless of reference montage (e.g., forehead and averaged mastoids)</div><div>- gel bridging, while theoretically possible, seems unlikely given that literally all EEG channels are (almost) identical</div><div><br></div><div>We're still investigating but wanted to hear if <span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span> </span>anyone ever observed anything like this? Were they able to solve it?</span></div><div><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><br></span></div><div><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">Thanks,</span></div><div><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><br></span></div><div><span style="color:rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">Roy</span></div></div>