2 Alternative Forced-Choice in SPSS


I conducted a research experiment using the constant stimuli method, with a 2 Alternative Forced-Choice (2AFC) test. I would like to fit a logistic regression to this data. The "scaled" logistic regression for a 2AFC is :

P(c) = 0.5 + 0.5(1/(1+e^-(b0 + b1*c))

Does anyone know if this can be implemented in SPSS, or if a data transformation could help? Thanks