Simon Task — Free Online Simon Effect Test

In the Simon task, a fixation point appears in the centre of the screen for 500 ms, and then a single red or blue circle shows up on the left or the right. Your job is to ignore where it appears and tap the button that matches its colour. Which button stands for red and which for blue is assigned at random for each session and shown before you start. You have 1.5 seconds to respond; after that the trial is recorded as a timeout. A random pause of 500–1000 ms separates the trials, so you cannot settle into a predictable rhythm and press ahead of time.

The session opens with 16 practice trials that tell you right away whether each answer was correct, so you can learn the colour–button pairing. If your practice accuracy falls below 75%, you are encouraged to practise once more. Then come 96 main trials, which take about 4 minutes and give no feedback. Exactly half of them (48) are congruent, with the circle on the same side as the correct button, and the other 48 are incongruent, with the circle on the opposite side. Comparing your responses in these two conditions is what the whole task is built around.

The headline number is your Simon effect: the median reaction time of your correct responses on incongruent trials minus the median on congruent trials, in milliseconds. Using the median keeps a few unusually slow or fast taps from distorting the result. At 0 ms or below, the circle's location did not slow you down; under 25 ms is a small effect; 25–59 ms is the typical range, since most people slow down by roughly 20–50 ms when location and button disagree; 60 ms or more is a large effect. Your overall accuracy and overall median reaction time are shown alongside it.

The detailed report breaks this down further: accuracy and median reaction time for each condition, an error-rate interference effect (incongruent minus congruent error rate), and a delta plot that sorts your correct responses into 4 speed bins. Location interference is usually largest in your fastest responses and shrinks in slower ones. Read speed and accuracy together: a small effect paired with extra errors on incongruent trials can simply mean you answered fast and let mistakes slip through. Fatigue, short sleep, distractions and the touch responsiveness of your device all shift the numbers, so treat one result as a snapshot of the day rather than a verdict about you.

The task goes back to Simon and Rudell (1967), who showed that an irrelevant cue — which side a sound came from — changed how quickly people responded, even though it had nothing to do with what they were asked to do. This page applies the same principle visually: the side where the circle appears automatically readies the hand on that side, and you have to override that pull to answer by colour alone. This stimulus–response compatibility effect has been widely used in research on cognitive control, and Soundary's task is its own web implementation of this published paradigm.

Your results are saved, so when you retake the task you can compare your new Simon effect with your previous one. Because each condition has 48 trials, a difference of a few milliseconds between two runs can easily be chance, so look at the trend across several sessions instead. The first run often includes some learning of the colour–button pairing, and the pairing is randomized again every time. For a fair comparison, use the same device, a similar time of day and the same way of holding it, and leave at least a few days between runs.