Like nature, consciousness apparently abhors a vacuumwhich may sometimes fool us into thinking the second hand on a clock takes an extra moment to tick, according to new research. Brain scientists have found that when we glance at something like a flashing cursor on a computer screen, our brains expand the new perception to make up for the time our eyes took to move. This effect happens all the time, but we only notice it when we look at something that changes at regular intervals. The results of this study, which appears today in the journal Nature, suggest that the conscious mind is occasionally more interested in continuity than accuracy.

Kielan Yarrow of London's Institute of Neurology and colleagues found that when individuals shifted their gaze from a fixed point on a computer screen to a counter that started going up from zero when their eyes first moved, they misjudged the length of the counter's first tick. Crucially, the longer their eyes had to travel to catch the counter, the farther off their judgments were. The illusion was shattered if study participants were able to see the counter sliding along the screen, however, ruining their impression that the counter had stayed the same while their eyes moved. "The brain's using this assumption that the target remains constant," Yarrow explains, "but [when] we violate that assumption by shifting the target the illusion is lost."

These findings fit well with the results of other studies that have revealed consciousness reconstructing our perception of the past based on events that take place later, Yarrow adds. For instance, when people receive two quick taps on the wrist followed by one on the elbow, they will sometimes perceive the tapping order as wrist-elbow-wrist. "It's not obvious why the brain should be reconstructing the past in this way," he says. "The question is whether this is saying something quite fundamental about the brain."