<div dir="ltr">Dear Kathleen,<div><br></div>> Can someone explain when one would want to select the "assume additive baseline" option when in the Study Function: ERSP. <div><br></div><div>This is my guess--the default ERSP baseline is (post-stimulus uV^2)/mean_across_time(pre-stimulus uV^2). This is to compute change ratio. This is why when we see 6dB increase in ERSP power, we say '200% power compared with baseline'. This approach has a merit in avoiding across-frequency normalization problem.</div><div><br></div><div>However, you can also take an average across conditions to compute baseline value, assuming the baseline calculation is additive, just like ordinary ERP baselines are. This approach does not make much sense if you think what ratio you are computing there...</div><div><span class="gmail-pl-pds" style="box-sizing:border-box;color:rgb(3,47,98);font-family:SFMono-Regular,Consolas,"Liberation Mono",Menlo,Courier,monospace;font-size:12px;white-space:pre;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial"><br></span></div><div>> After some searching we are still not clear on what this "additive" option </div><div><br></div><div>It's not clear to me either.</div><div><br></div><div>> Specifically, we would like to know what is happening with the baseline when we select, or don't select the additive baseline option? And does it matter if our epochs already have a baseline created during epoching</div><div> (our baseline is the first second of the three seconds before the trigger ).<br><br>If my guess is correct, then after doing it the mean baseline value in each condition could be non-zero, while the mean of the mean baseline values across condition should be zero. Personally I don't feel like testing it because I don't see a point in doing it.</div><div><br></div><div><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">> ERSP always compares post trigger data to that of the baseline, right?<span> </span></span><br></div><div><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span><br></span></span></div><div><span style="font-size:small;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline"><span>That's the default setting (all negative latency is counted as baseline). But you can also specify the baseline period explicitly.</span></span></div><div><br></div><div>Makoto<br><br><div class="gmail_quote"><div dir="ltr">On Tue, Jul 17, 2018 at 10:35 PM Kathleen Van Benthem <<a href="mailto:kathy_vanbenthem@carleton.ca">kathy_vanbenthem@carleton.ca</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div dir="auto"><blockquote type="cite">Dear List,<br></blockquote><blockquote type="cite"><div><span>Can someone explain when <div style="font-family:arial,helvetica,sans-serif;font-size:small;display:inline">one would want to</div> <div style="font-family:arial,helvetica,sans-serif;font-size:small;display:inline">select</div> the "assume additive baseline" option<div style="font-family:arial,helvetica,sans-serif;font-size:small;display:inline"> when in the Study Function: ERSP</div>. </span></div><div><span>After some searching we are still not clear on what this<div style="font-family:arial,helvetica,sans-serif;font-size:small;display:inline"> "additive" option</div> does in the Stud<div style="font-family:arial,helvetica,sans-serif;font-size:small;display:inline">y ERSP</div> function.</span><br><span>We are interested comparing power in frequency bands in the few seconds before the "responded to" vs. the "ignored" triggers (auditory cues)<div style="font-family:arial,helvetica,sans-serif;font-size:small;display:inline"> (N=30, two conditions per participant)</div>.</span><br><span></span><br><span><div style="font-family:arial,helvetica,sans-serif;font-size:small;display:inline">Specifically, we would like to know what </div>is happening with the <div style="font-family:arial,helvetica,sans-serif;font-size:small;display:inline">baseline</div> when we select, or don't select the additive baseline option? And does it matter if our epochs already have a baseline<div style="font-family:arial,helvetica,sans-serif;font-size:small;display:inline"> created during epoching</div> (<div style="font-family:arial,helvetica,sans-serif;font-size:small;display:inline">our baseline is </div>the first second of the three seconds before the trigger<div style="font-family:arial,helvetica,sans-serif;font-size:small;display:inline"></div>).</span><br><span></span><br><span>ERSP always compares post trigger data to that of the baseline, right? </span><br><span>Thanks for your help in this matter,</span><br><br><span>Kathleen Van Benthem </span><br><span><a href="mailto:kathy.vanbenthem@carleton.ca" target="_blank">kathy.vanbenthem@carleton.ca</a></span></div></blockquote></div></div><br></div>
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