Researchers are divided over whether the nerve circuits that handle this skill have a role in constructing a conscious awareness of the passing of time, but John Wearden, a psychologist at the University of Manchester, is sceptical. He thinks the same is true of our ability to discriminate between very short flashes of light or sound of different durations, a skffl which some researchers claim is accurate to a phenomenal 1 part in 10 000. At the other extreme is our percepfion of the passing of hours, days, weeks and years. Here again, argues Wearden, there is no direct monitoring of time by the brain. Instead, we seem to rely on our memory of how many events filled a period.
Distortions are commonplace.
Psychological studies show that our memories tend to retrospectively shrink empty minutes, hours and days while magnifying action-packed ones. Wearden believes this helps to explain why landmark events such as Christmas seem to come round faster each year. Over this range the brain seems to measure the passage of time directly and with astonishing accuracy. In a typical test at Wearden's laboratory, subjects would be asked to press a key after half a second had elapsed, or 0.7 seconds or some other short interval. After a little training, during which subjects would receive feedback on their performance, their average estimates were accurate to within a few per cent.