Z=zpoint(X,ADJ);

function Z=zpoint(X,ADJ);
% function Z=zpoint(X,ADJ)
%
% gives the Z-points (normal distribution) of the points making up a psychophysical curve.
% Hence X ranges from 0 to 1
% 
% If the values are out of bounds the function returns NaN.
% Values of X, 0 and to 1 (which would give -Inf and +Inf) are replaced. The program replaces them with 0.01 and 0.99. 
% However you can change this rescaling by setting the parameter ADJ. (ADJ=0.01 means 0.01---0.99) 
%
% Version 1.00
%
if nargin==1
ADJ=0.01;
end

if ADJ<0.0001
    ADJ=0.0001
elseif ADJ>0.2
    ADJ=0.2
end


X=X*(1-2*ADJ)+ADJ;
Z=-sqrt(2)*erfcinv(2*X);