From Perry Bebbington
You say that White’s illusion makes the grey stripes on a black line look darker, and on a white line look lighter (6 October, p 31). I experienced the opposite effect with the example given: the grey stripes on the black lines look lighter than the ones on the white lines. Do I have unusual vision in some way?
• Sorry, we inverted our description. You see what everyone else sees: the grey stripes look lighter when they are within the black line.
Nuthall, Nottinghamshire, UK
