options ls=80; options formdlim='-';
*edit the path below for your file location;
filename name 'C:\Users\decar\Desktop\Ennis_3AFC\Ennis_ss.txt';
DATA first;
  infile name delimiter=' ' firstobs=2;
  input x y z z1 z2; trial=_N_; resp=1;
  if y=1 then i1=1; if y=1 then i2=0; if y=1 then i3=0;
  if y=2 then i1=0; if y=2 then i2=1; if y=2 then i3=0;
  if y=3 then i1=0; if y=3 then i2=0; if y=3 then i3=1;
  output;
 keep trial x y resp z z1 z2 i1 i2 i3;
 RUN;
proc nlmixed data=first qpoints=11;
  parms b1-b2=0 d=0;
  eta1 = (b1-b2+d*z+eps1)*i1+(-b1+b2-d*z+eps2)*i2+(-b1+d*z1+eps3)*i3;
  eta2 = (b1-d*z1+eps1)*i1+(b2-d*z2+eps2)*i2+(-b2+d*z2+eps3)*i3;
  p = probnorm(eta1)*probnorm(eta2);
  model resp ~ binary(p);
  random eps1 eps2 eps3 ~ normal([0,0,0],[1,0,1,0,0,1]) SUBJECT=trial;
  predict p out=predprob;
  ods output parameterestimates=subjparm;
run;