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I have data from stimulation of subjects with different intensities (say we have 54 different intensities), and what follows is the percentage of them recognizing the respective stimulation:

x =    [0   0   0   0.50    0   0   0   0   0   0   0.5 0   0   0   0   0   0   0   0.125000000000000   0   0.333333333333333   0   0   0.111111111111111   0   0.428571428571429   0   0.285714285714286   0.166666666666667   0   0.1 0   0.400000000000000   0.5 0.4 0.25    0.6 0.727272727272727   0.714285714285714   0.25    0.666666666666667   0.777777777777778   1   0.75    0   1   0.9375  1   1   1   1   1   0.92    0.92]

Say the first index is the weakest stimulation, and the last index the strongest, as visible the stronger the stimulation the more likely the subject recognizes it. I want to fit now a distribution to these values, to get something called a psychophysical curve (looks like this).

What I have tried is:

pd = fitdist(x,distribution);

but this throws an error, I assume because of the 0's in the x array. What could I do alternatively?

TestGuest
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  • You could try fitting it with [logistic regression](https://en.wikipedia.org/wiki/Logistic_regression#Logistic_function,_odds,_odds_ratio,_and_logit). I can't tell you how to do that with matlab, but it worked quite nicely in my stats package with the vector of data you supplied. – pjs Dec 13 '17 at 00:28
  • Yes, I am aware that different distributions can be chosen, but I am interested in understanding the implementation in matlab – TestGuest Dec 13 '17 at 00:32

1 Answers1

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As suggested in

Fit a sigmoid to my data using MATLAB

"I think you can use "Curve fitting" App in Matlab. you can find it in APPS, in "Math, statistics and optimization" section."

What you have to do is define two vector of the same length:

  • one with the stimuli
  • one with the respone

After, looking at your file, you can try ,using the "Curve Fitting" app in matlab, to fit a sigmoid.

After pressing the generate code button, matlab will create a fuction that will give the same result.

Andrea Perissinotto
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