Sometimes, a normal spatial compatibility effect can be "reversed". That happens when people respond more quickly in the stimulus-response incompatible condition than in the stimulus-response compatible situation. The ABBA effect, first described by Stoet & Hommel (1999), is an example of this.

A more detailed description of the task can be found here.

In short, in the ABBA effect, you carry out two different simple responses to two different stimuli. The first stimulus (called Stimulus A) is viewed, a response is planned but withheld until the end of the trial. Then a second stimulus (called Stimulus B) is shown and the participant must respond immediately (Response B). Then, the participant must finish the trial with the final response A, which should hopefully still linger in short term memory. The whole trial takes around 6 seconds. Below is a schematic image of the idea.

About this implementation

There are 10 training trials and 100 main trials. The trials might feel as happening in a somewhat "slow" manner. This is because there is a delay of a few seconds between stimulus A and B (during which you just need to wait). At the end of the demo, you will see your own response-incompatibility effect.

Run the demo

In the demo, you will use four keys of your keyboard, the a and s on the left side, and the k and l on the right side. You plan a response (one or two key presses with the s or k button), and then later you need to respond directly with a a or l button press. Detailed instructions are in the demo.

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 for your data analysis.

Colum Meaning


location of planned response (response A, "L" or "R")


location of the immedeate response (response B, "L" or "R")


location of the immedeate response (response B, 1 or 2)


number of responses for response A


first response time (to response B)


first response time for response A (the planned response)


second response time for response A (if a second response is needed)


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

  • Stoet, G. and Hommel, B. (1999). Action planning and the temporal binding of response codes. Journal of Experimental Psychology: Human Perception and Performance, 25, 1625-1640.

  • Stoet, G. & Hommel, B. (2002). In Prinz, W. & Hommel, B. (Eds.). Interaction between feature binding in perception and action. Common mechanisms in perception and action: Attention and Performance, Vol. XIX (pp. 538-552). Oxford: Oxford University Press.