function[obj h] = pupil_response_function(obj, t, n=10.1, t_max=930, f=1/(10^27))

%%  Hoeks and Levelt, Behavior Research Methods 1993, vol 25(1) pp 16-26:
%  
%   Parameters of the Erlang Gamma are n, t_max
%   # n+1 = number of laters
%   # t_max = response maximum
%   # f = scaling factor
%
%   Erlang Gamma = Gamma distribution with shape parameter (k) set to an integer
%   For more information, see: https://en.wikipedia.org/wiki/Erlang_distribution
%
%   Hoeks and Levelt reported for n a range of 10.1 +/- 4.1, 
%   NB: They question the use of 10.1 as a value for all subjects,
%   but following deconvolution this is a minor issue.
%
%   t_max value reported in H&L : 930 ms with a standard deviation of 190
%   ms.
%

h = f.*(t.^n) .* exp(-n .*t ./ t_max);
h(0) = 0;