What It Cannot Be
One orange vertical bar, hidden in a field of bars that are orange, or vertical, but never both. Everyone knows a fuller screen is slower. This one fills up with items that are the wrong colour to be the answer, and asks your hands whether you paid for them.
A field of small bars appears. Somewhere in it there may be one orange vertical bar, and that is the only thing you are looking for. Press J if it is there, F if it is not. Everything else is orange lying down, or blue standing up, so nothing on the screen can be ruled in or out by one feature alone.
Half the displays contain it. Orange and blue were picked to stay apart for the common colour vision deficiencies, and there is a drill first that will tell you if they do not.
A conjunction like this cannot be picked out by any single feature, and the standard explanation is that attention therefore has to visit the items one at a time. Read that once more: it says attention visits the ITEMS. All of them, including the blue ones, which you can see are blue without visiting anything.
So two things move here, separately. Sometimes the screen stays full at 24 bars and only the number of ORANGE ones changes. Sometimes the orange ones stay at 3 and the screen fills up with blue. If a blue bar costs what an orange one costs, both feel the same. If it costs nothing, only the first one does anything to you.
- A 16 item drill, 14 practice displays, then 6 blocks of 46. About eleven minutes.
- Speed and accuracy both matter. Errors are dropped from the timing rather than punished.
- Keep your eyes on the centre dot until the display appears. Then hunt.
- Stay on the tab. Time spent away is counted and can void the session.
- Everything is computed in your browser. Nothing is recorded, nothing is sent anywhere.