I have used a Cumulative Gaussian function to fit the data I got from a 2AFC experiment. How can I calculate the point of subjective equality using the Palamedes toolbox for matlab or the psignifit toolbox?
It is a crowding experiment aimed to find which distance of target from flankers produces the strongest crowding effects. The flankers will always be gabors with horiz orientation and the target will have some tilt from the horiz (4 tilt levels). The conditions are: baseline, in which only the target appears, 1st experimental, in which the target and the flankers appear with distance x1 and the 2nd experimental in which the target appears with the flankers in distance x2.
In every trial I will have one of the tilt levels for the target (presented with the method of contant stimuli) and the participant will have to reply if the target is tilted CW or CCW with respect to the horizontal axis. For my analysis I will store for every tilt level the percent of the trials for which the reply was “CW” and I will plot this data as a function of tilt level. So the y axis must be from 0 to 1. In these data I want to use the max likelihood criterion to fit a normal cdf and find the discrimination threshold and std error of that threshold