Bending Time's Arrow

Among my parenting memorabilia is an illustrated timeline my son made back in the second grade. It starts with his 1986 birthday on the left and proceeds through various milestones of his first years—first day of kindergarten, T-ball, and so forth—ending on the far right with another celebration at the ripe old age of seven. I treasure this.

But how did he know that life unfolds from left to right, and not the other way around? Sure, his teacher instructed him and his classmates to draw the timeline this way, but why? Why do we accept without question that left equals early while right equals late, far off in time? More fundamentally, why do we entwine time and space?

Psychologists suspect that this space-time continuum may be more than a social convention, an artifice that we all simply agree to. Perhaps the brain has wired our perceptions of space and time together for some reason. A team of researchers has been exploring this question in the laboratory, using an unusual pair of spectacles.

Psychologist Francesca Frassinetti of the University of Bologna and her colleagues wanted to see if deliberately distorting space perception would also distort perception of the passage of time. They had a group of volunteers look at an image on a computer screen for different intervals of time—say two seconds. Then a different image appeared on the screen, and the volunteers tried to keep it on the screen for exactly the same amount of time, using a controller. In other words, they tried to duplicate the interval of time they had just perceived.

Most of the volunteers were pretty good at this, but that wasn’t the point. After the initial test, all of the volunteers put on special glasses, called prismatic lenses. These glasses shifted the volunteers’ perception of the image horizontally, either to the left or to the right; that is, they would look at the image just as before, but it would appear to the left or the right. They were basically forced to shift their spatial attention. Then they all did the same time estimation task as before.

The results were clear, and a bit spooky. As reported in the June issue of the journal Psychological Science, when the glasses shifted the volunteers’ attention to the right, they overestimated time. Not to put too fine a point on it, time hurried by; it expanded in their minds. Similarly, shifting the brain’s focus to the left compressed time; time intervals seemed shorter than they were in fact.

This doesn’t explain why time’s arrow moves from left to right, but it does show that time's on a horizontal line in the mind's eye. And it does help explain something else about my son’s timeline. A lot of time and experience is compressed into a very small space early on in his young life, with each year taking up more space as he gets older. It makes intuitive sense that we would experience time as expanding into the future, where the exact dimensions of our experience are as yet unknown.

For more insights into the quirks of human nature, visit “We’re Only Human” at www.psychologicalscience.org/onlyhuman. Selections from the blog also appear regularly in the magazine Scientific American Mind and at Newsweek.com.