<div dir="ltr"><div class="gmail_default" style="color:rgb(51,51,153)"><br></div><div class="gmail_default" style="color:rgb(51,51,153)">*********EXTRA NOTE for COURTNEY </div><div class="gmail_default" style="color:rgb(51,51,153)"><br></div><div class="gmail_default" style="color:rgb(51,51,153)">Hello, This is a brief followup about your question regarding negative values in spectopo. In brief, the reason why the values are negative in spectopo results is because eeglab developers made it so that the values are transformed to dB, which leads to some negative values. You can find out more about dB computation by examining various resources on computing spectra for EEG.</div><div class="gmail_default" style="color:rgb(51,51,153)">As always, you can google for more information by searching for something like the following: eeglablist spectopo db</div><div class="gmail_default" style="color:rgb(51,51,153)"><br></div><div class="gmail_default" style="color:rgb(51,51,153)">See also the books and resources that I have suggested previously. Good luck with your adventures in learning more about basic spectral computation!</div><div class="gmail_default" style="color:rgb(51,51,153)"><br></div><div class="gmail_default" style="color:rgb(51,51,153)">The link below shows an image for the same spectopo result image with spectopo code running normally (where some values are negative), and with dB computation turned off in the code (where the values are all positive)</div><div class="gmail_default" style="color:rgb(51,51,153)"><br></div><div class="gmail_default" style="color:rgb(51,51,153)">The image on the left is the normal image with spectopo running normally.</div><div class="gmail_default" style="color:rgb(51,51,153)"><br></div><div class="gmail_default" style="color:rgb(51,51,153)">The image on the right is without negative values, with the following line in the spectopo function.</div><div class="gmail_default" style="color:rgb(51,51,153)">
<p class="gmail-p1">eegspecdB = 10*log10(eegspecdB);</p><p class="gmail-p1">changed to eegspecdB = eegspecdB;</p></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399">The LINK TO THE IMAGE for COURTNEY:</font></div><div class="gmail_default"><font color="#333399"><a href="https://ibb.co/iyiwXm">https://ibb.co/iyiwXm</a></font><br></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399">Note that the spectopo function is called by pop_spectopo, and the documentation on each is easily reviewed by looking into both functions, as you would with any other function in matlab. The change described above was done by entering the function itself, finding the place where the values are transformed to dB, and essentially "turning off" that computation, as per the code change detailed above. Note that you should be saavy with matlab coding, and with spectral computation, in order to make such changes safely and in a principled manner.</font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399">ps. some specific hints about this came from the google groups page for Mike X. Cohen's Time-Frequency book, found via the suggested google search listed above. </font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399">pps. Note there are many ways to get spectral output, such via Matlab without eeglab, via eeglab, via Chronux, via other eeg analysis toolboxes for matlab, and via other codes/scripts such as those provided in Cohen's books. Overall it is best to learn how to compute spectra by hand so one has a better handle on what is happening "under the hood". That is of course much better than just "trusting" functions to do things. </font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div><div class="gmail_default"><font color="#333399"><br></font></div></div>