What you will learn in this lesson


Spatial compatibility is an important concept in research regarding attention, perception, and action planning. Typically, people respond faster when a stimulus and response are compatible with one another, for example when they are both on the same side of the body (see the lesson about stimulus-response compatibility).

Sometimes, the spatial compatibility effect is "reversed". In that situation, people respond more quickly in the stimulus incompatible situation than in the stimulus compatible situation. There are only a few demonstrations of this. For example, one can argue that the Inhibition Of Return (IOR) effect is an example of reversed stimulus-response compatibility (see the lesson about IOR). The example this lesson is about is the ABBA effect, first described by Stoet & Hommel in 1999 (see reading material at the bottom of this lesson).

Disambiguation of the name ABBA

The name ABBA is also known as a 1970s Swedish pop group which won the Eurovision festival with this song in 1974. The video is worth watching purely out of historical interest and how things have changed. This experiment and phenomenon have absolutely nothing to do with that group or song.

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 picture of a trial in the ABBA paradigm.


Now you understand why it is called ABBA. It is about the sequence of stimuli and responses. You see stimulus B and respond to stimulus B when you are keeping a prepare response in memory. The memory of the prepared response A <b>interferes</b> with the stimulus B - response B task.

The theory behind it is called "code occupation theory". The idea is that if people have used "event" codes to encode response A, these codes are less available for subsequent and different cognitive processes. If the planned response A and the to-be-carried-out response B are on the same side, some of the event codes are already bound in plan A, so to speak. This makes that people are slower to respond with the left finger if a left finger response (or even left foot) response is already been planned and the event code "left" is already bound to a different action plan.

Do it yourself

In this demonstration, 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 button S or K), and then later you need to respond directly with a A or L key. Detailed instructions are presented in the demo. Note that there are 10 training trials and 100 main trials. The trials run somewhat slowly, because there is a delay of a few seconds between stimulus A and B (during which you just need to wait). At the end, you will see your own response-incompatibility effect.

Reading material