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THE perception of 鈥渘ow鈥� varies from person to person, researchers in Britain
have found.

Jim Stone and his colleagues at the University of Sheffield looked at
differences in the time it takes for audio and visual stimuli to reach people鈥檚
consciousness. They showed volunteers a red light and played a tone, with
anything up to a quarter of a second between the two.

Sometimes the light came first, sometimes the sound and sometimes they
occurred simultaneously. The test was repeated 1000 times for each of the 17
volunteers, who were asked to say whether the light and the sound happened at
exactly the same time.

Stone was surprised to find that some people reported the events as
simultaneous when the light preceded the sound by up to 150 milliseconds. Others
did so when the sound came before the light.

To find out if people take into account the time it takes sounds to travel to
them from distant sources, Stone repeated the experiment with the sound coming
from about 4 metres away, taking an extra 11 milliseconds to reach the
volunteers. None of them took the extra distance into account when reporting
simultaneous events, Stone found. But he was astonished by how consistent each
individual鈥檚 judgements remained鈥攅xactly 11 milliseconds off their
original judgements.

It doesn鈥檛 seem to matter if different people have different ideas about
whether events are simultaneous, Stone concludes鈥攂ut personal consistency
is vital. 鈥淚t should be rock-solid stable,鈥� he says, 鈥渙therwise you wouldn鈥檛 be
able to play ping-pong.鈥�