How does spot the difference work?
Two pictures of the same scene sit side by side, and 5 things differ between them: a colour, something missing, or something smaller. Tap a difference in either picture and a circle marks it in both. A tap on something that hasn't changed is a wrong tap. The clock stops when you find the last one.
Every scene is drawn fresh for each game from simple shapes (a sun, clouds, a house, trees, flowers, birds and a balloon) placed at random, so you can't learn the answers. The changes never overlap, so one tap can only ever find one of them, and which picture holds the changes is random too. The site's tests build hundreds of scenes and check that exactly 5 things differ in each.
How is your result calculated?
Your result is the time from the moment the pictures appear to your last find. Wrong taps are counted and shown with it, but they add no time. If you press "Show me", the game ends there: the differences you missed are circled, and your result is how many you found.
Why are the differences hard to see?
Because you can't look at both pictures at once. Your eyes jump from one to the other, and you compare what you see with what you remember from a moment ago, which is only the part you were paying attention to. Missing a change this way is called change blindness.
Ronald Rensink, Kevin O'Regan and James Clark showed how strong it is in a 1997 study in Psychological Science: with a brief blank between two versions of a photo, people took many cycles to spot even large changes. The Change Blindness Test uses that method; here, each jump of your eyes between the pictures plays the part of the blank.
How to spot differences faster
- Go one thing at a time. Pick an object, look at it in both pictures, then move to the next. Sweeping the whole picture misses small changes.
- Work in strips. Do the sky, then the ground, so you don't check the same corner twice.
- Count as well as look. A missing flower or bird is easier to catch by counting them than by looking for a gap.
For a search for one odd item among many, try Visual Search; for remembering where things were, Memory Match.