/usr/share/psychtoolbox-3/Quest/QuestQuantile.m is in psychtoolbox-3-common 3.0.11.20140816.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 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 | function t=QuestQuantile(q,quantileOrder)
% intensity=QuestQuantile(q,[quantileOrder])
%
% Gets a quantile of the pdf in the struct q. You may specify the desired
% quantileOrder, e.g. 0.5 for median, or, making two calls, 0.05 and 0.95
% for a 90% confidence interval. If the "quantileOrder" argument is not
% supplied, then it's taken from the "q" struct. QuestCreate uses
% QuestRecompute to compute the optimal quantileOrder and saves that in the
% "q" struct; this quantileOrder yields a quantile that is the most
% informative intensity for the next trial.
%
% This is based on work presented at a conference, but otherwise unpublished:
% Pelli, D. G. (1987). The ideal psychometric procedure. Investigative
% Ophthalmology & Visual Science, 28(Suppl), 366.
%
% See Quest.
% Denis Pelli, 6/9/96
% 6/17/96 dgp, worked around "nonmonotonic" (i.e. not strictly monotonic)
% interp1 error.
% 3/1/97 dgp updated to use Matlab 5 structs.
% 4/12/99 dgp removed support for Matlab 4.
%
% Copyright (c) 1996-1999 Denis Pelli
if nargin>2
error('Usage: intensity=QuestQuantile(q,[quantileOrder])')
end
if length(q)>1
if nargin>1
error('Can''t accept quantileOrder for q vector. Set each q.quantileOrder instead.')
end
t=zeros(size(q));
for i=1:length(q(:))
t(i)=QuestQuantile(q(i));
end
return
end
if nargin<2
quantileOrder=q.quantileOrder;
end
p=cumsum(q.pdf);
if ~isfinite(p(end))
error('pdf is not finite')
end
if p(end)==0
error('pdf is all zero')
end
index=find(diff([-1 p])>0);
if length(index)<2
error(sprintf('pdf has only %g nonzero point(s)',length(index)))
end
t=q.tGuess+interp1(p(index),q.x(index),quantileOrder*p(end)); % 40 ms
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