6.6.1. In Action
In the mid-’90s, Salvatore Aglioti1 and colleagues showed that when people are presented with the Ebbinghaus illusion (see Figure 6-6) they find the disk surrounded by smaller circles seems larger than an identically sized disk surrounded by larger circles, and yet, when they reach for the central disks, they use the same, appropriate, finger-thumb grip shape for both disks. The brain’s conscious perceptual system (the ventral pathway) appears to have been tricked by the visual illusion, whereas the brain’s visuomotor (hand-eye) system (the dorsal pathway) appears immune.
There are many examples of situations in which our perception seems to be tricked while our brain’s visuomotor system remains immune. Here’s one you can try. You’ll need a friend and a tape measure. Find a sandy beach so you can draw in the sand or a tarmac area where you can draw on the ground with chalk. Tell your friend to look away while you prepare things.
6.6.1.1 Part 1
Draw a line in the sand, between 2 and 3 meters long. Now draw a disk at the end, about 70 cm in diameter, as in Figure 6-7A. Ask your friend to stand so her toes are at the start of the line, with the disk at far end, and get her to estimate how long the line is, using whichever units she’s happy with. Then blindfold her, turn her 90°, and get her to pace out how long she thinks the line is. Measure her “walked” estimate with your tape measure.
6.6.1.2 Part 2
Tell your friend to look away again, get rid of the first line, and draw another one of identical length. (You could use another length if you think your friend might suspect what’s going onit just makes comparing estimates easier if you use the same length twice.) This time, draw the disk at the end so that it overlays the line, as in Figure 6-7B. Now do exactly as before: get your friend to stand with her toes at the line start and guess the length verbally from where she is, blindfold her, and ask her to walk the same length as she thinks the line is.
Taken from : Mind Hacks
