mxflat

function [blocking, chan]=mxflat(data,max_vertical,max_length)

mxflat returns epochs that appear to contain amplifier blocking

Inputs:
data: a 3-D array of EEG data (channel,time,epoch)

max_vertical: if two consecutive points differ by this value, then
they are assumed not to be part of a segment of amplifier
blocking. A good value for this is .2 microvolts.

max_length: if more than max_length consecutive points do not
differ by more than max_verticle from the initial consecutive
point, the epoch is assumed to contaminated by blocking.  A good
value for this is 10 time points.

Output:
blocked: a 1-D binary array.  a 1 in the nth position of the
array indicates that the nth epoch contains blocking

chan: a 1-D integer array.  Lists the channel in which blocking
was detected for each epoch specified by "blocked"

0001 function [blocked, chan]=mxflat(data,max_vertical,max_length)
0002 %function [blocking, chan]=mxflat(data,max_vertical,max_length)
0003 %
0004 %mxflat returns epochs that appear to contain amplifier blocking
0005 %
0006 %Inputs:
0007 %data: a 3-D array of EEG data (channel,time,epoch)
0008 %
0009 %max_vertical: if two consecutive points differ by this value, then
0010 %they are assumed not to be part of a segment of amplifier
0011 %blocking. A good value for this is .2 microvolts.
0012 %
0013 %max_length: if more than max_length consecutive points do not
0014 %differ by more than max_verticle from the initial consecutive
0015 %point, the epoch is assumed to contaminated by blocking.  A good
0016 %value for this is 10 time points.
0017 %
0018 %Output:
0019 %blocked: a 1-D binary array.  a 1 in the nth position of the
0020 %array indicates that the nth epoch contains blocking
0021 %
0022 %chan: a 1-D integer array.  Lists the channel in which blocking
0023 %was detected for each epoch specified by "blocked"
0024 %
0025 
0026 s=size(data);
0027 if length(s)~=3
0028   disp('Data should be 3 dimensional');
0029   return
0030 end
0031 
0032 nepochs=s(3);
0033 
0034 chan=[];
0035 blocked=[];
0036 for a=1:s(3) %number of epochs
0037   blocking(a)=0;
0038   for c=1:s(1) %number of channels
0039     mn=data(c,1,a);
0040     len=1;
0041     for b=2:s(2) %number of points/epoch
0042       %fprintf('%d time %d len\n',b,len);
0043       if (abs(data(c,b,a)-mn)>max_vertical)
0044     len=1;
0045     mn=data(c,b,a);
0046       else
0047     len=len+1;
0048       end
0049       
0050       if len>max_length
0051     blocking(a)=1;
0052     chan=[chan c];
0053     blocked=[blocked a];
0054     break;
0055       end
0056     end
0057     if (blocking(a))
0058       break;
0059     end
0060   end
0061 end