I02 Whose Face Is It

It all happens within a few seconds of two children standing on either side of the wall. Two images then reach each child's eyes at once - their own and someone else's - and the brain can't stand a picture in pieces, so it instantly sticks them together into one face and fills in what is missing at the join. How do we know it is science and not just pulling faces? As early as the 19th century Hermann von Helmholtz argued that sight is not a faithful photograph but constant guesswork, and the Gestalt psychologists described how the brain completes unfinished shapes. The wall turns this theory into an experiment you can check with your own eyes.

For the illusion to keep working for years, the mirror surface has to stay smooth: only polished metal reflects rays evenly and gives a clear image. The mirror is not glass: the strips are made of polished stainless steel, so they do not break or rust. The frame is steel, galvanised and powder-coated, so it withstands rain, frost and sun. The wall works outdoors all year round, winter included. It needs no electricity or water connection - daylight is enough. The manufacturer is EduPlayground; the equipment is made in Poland and covered by a warranty.