returns a hemodynamic response function
FORMAT [hrf,p] = pr_spm_hrf(RT,[p]);
RT - scan repeat time
p - parameters of the response function (two gamma functions)
defaults
(seconds)
p(1) - delay of response (relative to onset) 6
p(2) - delay of undershoot (relative to onset) 16
p(3) - dispersion of response 1
p(4) - dispersion of undershoot 1
p(5) - ratio of response to undershoot 6
p(6) - onset (seconds) 0
p(7) - length of kernel (seconds) 32
hrf - hemodynamic response function
p - parameters of the response function
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@(#)spm_hrf.m 2.8 Karl Friston 02/07/31
0001 function [hrf,p] = pr_spm_hrf(RT,P); 0002 % returns a hemodynamic response function 0003 % FORMAT [hrf,p] = pr_spm_hrf(RT,[p]); 0004 % RT - scan repeat time 0005 % p - parameters of the response function (two gamma functions) 0006 % 0007 % defaults 0008 % (seconds) 0009 % p(1) - delay of response (relative to onset) 6 0010 % p(2) - delay of undershoot (relative to onset) 16 0011 % p(3) - dispersion of response 1 0012 % p(4) - dispersion of undershoot 1 0013 % p(5) - ratio of response to undershoot 6 0014 % p(6) - onset (seconds) 0 0015 % p(7) - length of kernel (seconds) 32 0016 % 0017 % hrf - hemodynamic response function 0018 % p - parameters of the response function 0019 %_______________________________________________________________________ 0020 % @(#)spm_hrf.m 2.8 Karl Friston 02/07/31 0021 0022 % global parameter 0023 %----------------------------------------------------------------------- 0024 global defaults 0025 if ~isempty(defaults), 0026 fMRI_T = defaults.stats.fmri.t; 0027 else, 0028 fMRI_T = 16; 0029 end; 0030 0031 % default parameters 0032 %----------------------------------------------------------------------- 0033 p = [6 16 1 1 6 0 32]; 0034 if nargin > 1 0035 p(1:length(P)) = P; 0036 end 0037 0038 % modelled hemodynamic response function - {mixture of Gammas} 0039 %----------------------------------------------------------------------- 0040 dt = RT/fMRI_T; 0041 u = [0:(p(7)/dt)] - p(6)/dt; 0042 hrf = spm_Gpdf(u,p(1)/p(3),dt/p(3)) - spm_Gpdf(u,p(2)/p(4),dt/p(4))/p(5); 0043 hrf = hrf([0:(p(7)/RT)]*fMRI_T + 1); 0044 hrf = hrf'/sum(hrf);