function [channels,overall_amplitude] = eeg_amplitudearea(EEG, channels, resrate, wstart, wend)
% EEG_AMPLITUDEAREA - Resamples an ERP average using spline interpolation
% at a new sample rate (resrate) in Hz to get the exact limits
% of the window of integration. Finely samples the window
% and adds together very narrow rectangles capped by
% right-angled triangles under the window. Output is in uV.
% Trade-off between speed and number of resamples and number of
% channels selected occurs.
% Usage:
% >> [channels, amplitude] = eeg_amplitudearea(EEG,channels, resrate, wstart, wend);
% Inputs:
% EEG - EEGLAB data struct containing a (3-D) epoched data matrix
% channels - vector of channel indices
% resrate - resampling rate for window of integration in Hz
% wstart - start of window of integration in ms post stimulus-onset
% wend - end of window of integration in ms post stimulus-onset
%
% Outputs:
% channels - a vector of channel indices.
% amplitude - 1-dimensional array in uV for the channels
%
% Example
% >> [channels, amplitude] = eeg_amplitudearea(EEG,[12 18 25 29], 2000, 90.52, 120.52);
%
% Author: Tom Campbell, Helsinki Collegium for Advanced Studies, Biomag Laboratory,
% Engineering Centre, Helsinki University Central Hospital Helsinki Brain
% Research Centre (tom.campbell@helsinki.fi) Spartam nanctus es: Hanc exorna.
% Combined with AMPLITUDEAREA_MSUV by Darren Weber, UCSF 28/1/05
% Retested and debugged Tom Campbell 2/2/05
% Reconceived, factored somewhat, tested and debugged Tom Campbell 13:24 23.3.2005
if wstart > wend
error ('ERROR: wstart must be greater than wend')
else
[channels, overall_amplitude] = eeg_amplitudearea_msuV (EEG,channels, resrate, wstart, wend);
overall_amplitude = overall_amplitude/(wend - wstart);
end
return
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function [channels, overall_area] = eeg_amplitudearea_msuV (EEG, channels, resrate, wstart, wend)
%if ndim(EEG.data) ~= 3
% error('EEG.data must be 3-D data epochs');
%end
erp = mean(EEG.data,3);
[tmp ind1] =min( abs( EEG.times - wstart ) ); % closest time index to wstart
[tmp ind2] =min( abs( EEG.times - wend ) ); % closest time index to wend
restep = 1/resrate;
if EEG.times(ind1) > wstart
ind1= ind1 -1;
end
if EEG.times(ind2) < wend
ind2= ind2 +1;
end
for x= ind1:ind2
t = (x -ind1)+1;
tim(t) = EEG.times(x);
end
tr = 1;
timr(tr) = wstart;
while timr(tr) < wend
tr = tr + 1;
timr(tr) = timr(tr-1)+ restep;
end
for x = 1:size(channels,2)
channel = channels(x);
%resamples
rerp(x, 1:tr) = spline(tim(:),erp(channel, ind1:ind2), timr(1:tr));
pent = timr(tr - 1);
overall_area(x) = 0;
for y = 1:(tr -1)
v1 = rerp(x,(y));
v2 = rerp(x,(y+1));
if ((v1 > 0) && (v2 < 0)) || ((v1 < 0) && (v2 > 0))
if (y == (tr-1)) && (timr(y+1)> wend)
area1 = zero_crossing_truncated(v1, v2, restep, wend, pent);
else
area1 = zero_crossing(v1, v2, restep);
end
else
if( y == (tr-1)) && (timr(y+1)> wend)
area1 = rect_tri_truncated(v1, v2, restep,wend,pent);
else
area1 = rect_tri(v1, v2, restep);
end
end
overall_area(x) = overall_area(x) + area1;
end
end
return
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function [area] = zero_crossing(v1,v2,step)
if (v1 > v2)
T1 = v1;
T2 = v2;
else
T1 = v2;
T2 = v1;
end
tantheta = (abs(T1)+ abs(T2))/step;
if (v1 > v2)
%decline
z = abs(T1)/tantheta;
tr1= abs(T1)*(z/2);
tr2= abs(T2)*((step-z)/2);
else
%incline
z = abs(T2)/tantheta;
tr2= abs(T2)*(z/2);
tr1= abs(T1)*((step-z)/2);
end
[area] = (tr1 - tr2);
return
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function [area] = zero_crossing_truncated(v1,v2,step,wend,pent)
if (v1 > v2)
T1 = v1;
T2 = v2;
else
T1 = v2;
T2 = v1;
end
tantheta = (abs(T1)+ abs(T2))/step;
s = wend - pent;
if (v1 > v2)
z = abs(T1)/tantheta
if s < z
%decline,truncated before zerocrossing
t1 = tantheta * s;
r1 = abs(T1)-abs(t1);
tr1= abs(t1)*(s/2);
tr2= 0;
rect1 = r1*s;
rect2 = 0;
else
%decline,truncated after zerocrossing
t2= tantheta*(s-z);
tr1= abs(T1)*(z/2);
tr2 = abs(t2)*((s-z)/2);
rect1 = 0;
rect2 = 0;
end
else
z = abs(T2)/tantheta;
if s < z
%incline,truncated before zerocrossing
t2 = tantheta * s;
r2 = abs(T2)-abs(t2);
tr1= 0;
tr2= abs(t2)*(s/2);
rect1 = 0;
rect2 = r2*s;
else
%incline,truncated after zerocrossing
t1= tantheta*(s-z);
tr1 = abs(t1)*((s-z)/2);
tr2 = abs(T2) * (z/2);
rect1 = 0;
rect2 = 0;
end
end
[area] = ((rect1 + tr1) - (rect2 + tr2));
return
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function [area] = rect_tri(v1,v2,step)
if (abs(v1) > abs(v2))
T = abs(v1)-abs(v2);
R = abs(v2);
else
T = abs(v2)-abs(v1);
R = abs(v1);
end
rect = R*step;
tri = T*(step/2);
if v1 > 0
area = 1* (rect+tri);
else
area = -1 * (rect+tri);
end
return
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function [area] = rect_tri_truncated(v1,v2,step,wend,pent)
if (abs(v1) > abs(v2))
T = abs(v1)-abs(v2);
R = abs(v2);
else
T = abs(v2)-abs(v1);
R = abs(v1);
end
tantheta = abs(T)/step;
s = wend -pent;
if (v1>0)
if v1 >v2
%positive decline
t = tantheta*s;
e = abs(T)-abs(t);
rect = s*R;
exrect = s*e;
tri = (s/2)*R;
else
%positive incline
t = tantheta*s;
rect = s*R;
exrect = 0;
tri = (s/2)*R;
end
else
if v1 >v2
%negative decline
t = tantheta*s;
rect = s*R;
exrect = 0;
tri = (s/2)*R;
else
%negative incline
t = tantheta*s;
e = abs(T)-abs(t);
rect = s*R;
exrect = s*e;
tri = (s/2)*R;
end
end
tri = T*(step/2);
if v1 > 0
area = 1* (rect+exrect+tri);
else
area = -1 * (rect+exrect+tri);
end
return
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