/usr/share/psychtoolbox-3/Psychometric/FitLogitYN.m is in psychtoolbox-3-common 3.0.9+svn2579.dfsg1-1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 | function [a,b,thresh50] = FitLogistic(inputs,nYes,nNo)
% [a,b,thresh50] = FitLogistic(inputs,nYes,nNo)
%
% Fit a logistic function to YN psychometric data.
% Returns logistic parameters and 50% threshold.
%
% The form of the logistic equation is pYes = 1/(1+10^-(a*inputs+b))
%
% The logistic is not a good function to use for serious work,
% but you can do a quick and dirty fit analytically and
% you can explain it to students more easily than some
% other candidate models for psychometric functions.
%
% See also: FitLogistic, FitWeibYN, FitCumNormYN,
% InvertLogistic, ComputeLogistic.
%
% 2/8/97 dhb Wrote it.
% Make sure there are trials passed at all input levels.
% Ignore any input levels with no trials
pYes = nYes ./ (nYes + nNo);
index = find(~isnan(pYes));
if (isempty(index))
error('FItLogitYN: no input trials passed');
end
pYes = pYes(index);
inputs = inputs(index);
[a,b] = FitLogistic(inputs,pYes);
thresh50 = InvertLogistic(0.5,a,b);
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