This is a touchscreen friendly version of the Simon task.

The Simon task and the Simon effect are named after J. R. Simon. Together with his colleague, he first described this effect in 1963. In essence, it shows that people respond faster and more accurately if there is a match between stimulus and response features (e.g., location, when for example stimulus and response are both located on the left side of one’s body).

The effect is also known as a stimulus-response compatibility effect. There are many variants of the stimulus-response compatibility available. Like the Stroop effect, it is easy to notice consciously how difficult a mismatch between a stimulus and response can be.

About this implementation

This runs well on mobile phones too, in particular Android phones. It was originally developed for a Samsung J5, which has a 1280x720 screen resolution. Because in fully screen, it is always scaled so that the resolution is actually 640x360, that is what you have in the options line of the code as well.

Run the demo

In this task, you always see two circles, one colored and one white. The colored one is red or green. If it is red, you need to touch/click the left circle. If it is green, you need to touch/click the right circle.

The demo takes less than 2 minutes to complete.

Data output file

In PsyToolkit, the data output file is simply a textfile. The save line of the PsyToolkit experiment script determines what is being saved in the data output file. Typically, for each experimental trial, you would have exactly one line in your text file, and each number/word on that line gives you the information you need for your data analysis, such as the condition, response speed, and whether an error was made.

Meaning of the columns in the output datafile. You need this information only if you use this experiment for your research project.

Colum Meaning


Name of block


Congruent or incongruent (as a word)


Color (red or green)


Congruent or incongruent (as a number, 1=congruent or 2=incongruent)


Table row chosen


Status (1=correct, 2=wrong, 3=timeout)


Response Time (ms)


X-position of where stimulus was clicked/touched


Y-position of where stimulus was clicked/touched


If you have a PsyToolkit account, you can upload the zipfile directly to your PsyToolkit account. Watch a video on how to do that. If you want to upload the zipfile into your PsyToolkit account, make sure the file is not automatically uncompressed (some browsers, especially Mac Safari, by default uncompress zip files). Read here how to easily deal with this.

Further reading

Simon, J.R. and Wolf, J.D. (1963). Choice reaction times as a function of angular stimulus-response correspondence and age. Ergonomics, 6, 99-105.

Hommel, B. (1993). Inverting the Simon effect by intention: Determinants of direction and extent of effects of irrelevant spatial information. Psychological Research, 55, 270-279.

Prinz, W. & Hommel, B. (2002). Common mechanisms in perception and action: Attention and Performance, Vol. XIX. Oxford: Oxford University Press.