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."