Brightness task
As we have seen, the same luminance intensity can appear different when presented on backgrounds of differing intensity—the "simultaneous brightness contrast" illusion.
Here, you will measure the magnitude of the effect on your own perception by running a psychophysics experiment.
Instructions
Use the z and m keys to indicate whether the left or right central square, respectively, was brighter.
There will be a series of 110 trials, and will take 5 minutes or so to complete. The results will be shown immediately after in the graph below.
Note that refreshing the page or going to another site will lose your response data! Make sure you have completed the necessary activities before doing so.
If your responses aren't being received, make sure that the task window is 'active'. You can make the window active by clicking within it. The task window will have a blue border when it it is not active, and a black border when it is active.
Task
Results
The square on the left of the stimulus images is referred to as the 'comparison', and its luminance varied across trials. The square on the right of the stimulus images is referred to as the 'reference', and its luminance was 0.5 on every trial.
The figure below shows the proportion of trials in which you responded that the 'comparison' square seemed brighter than the 'reference' square (vertical axis), for a given luminance level of the 'comparison' (horizontal axis).