The Psychophysics Psyber Lab




Psychom_siml: programs for adaptive-tracking threshold estimation simulation.

Vit Drga

Download the zipped archive here:

I wrote C programs called psychom_siml_guts and psychom_siml_base for Monte Carlo simulations of adaptive-tracking threshold estimation (e.g., 2IFC two-up one-down, etc.). The idea is say you have an empirical psychometric function (e.g., 2IFC percent correct as a function of signal strength) and you have fitted a regression function to the data. In practice, you can only repeat the experiment a small number of times, but given the regression function and the Monte Carlo simulation program, you can simulate re-running the experiment a large number of times. This allows you to find out what the experiment might have shown had you run it using different adaptive-track step-sizes, stepping rules, or longer trial runs and different halting criteria. Furthermore, you'll get much better numerical estimates of the variability associated with your measurements.

Psychom_siml works for two-, three- and four-interval tasks, and is easily extendable to more intervals. It works for basic n-up-m-down stepping rules (nothing fancy yet like maximum-likelihood estimation). Results can be displayed to screen and saved in a spreadsheet-friendly text file. Psychom_siml caters for a variety of different types of regression function, primarily piecewise polynomial, linear and Gaussian cumulative distribution functions. Logistic-based functions have not been implemented yet, but you are free to modify the code (see below).

The program runs from the command-line (no GUI for portability reasons) and has been tested in in GNU/linux and in Windows. The C source files and a Windows-executable file can be downloaded in a zipped archive here: If running in Windows, you will need the file cygwin1.dll (download from here as a zipped archive: to be present in the same directory as psychom_siml_guts.exe. Cygwin1.dll (v1.3.22) is kindly made available under the GNU Public License and the source code for that is available at (or in the same subdirectory of any cygwin mirror). I like the GNU idea of free, open source software (see the GNU manifesto). These psychom_siml programs are copyright under the GNU Public License (see the source .c files). This means you are free to modify the code as you wish and redistribute any program based on your modifications so long as you also make freely available your modified source code along with the program. There is extensive documentation for the psychom_siml programs in the README files in the zipped-up archive.

If you have any queries, please contact me using this form.

Last updated 08 Nov 2009 04:37 PM

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