“Visualize the ball.”

I’m sure most of you have heard the phrase at some point in your life — for me it was probably as long ago as 9th grade gym class and had more to do with not getting hit by it than trying to catch it, but still — we’ve all heard the words.

And we might think that visualizing an imaginary ball would enhance our ability to see the actual ball once it’s headed our direction. But research dating back to the early 20th century suggests the opposite. The Perky Effect, named for the man who coined it in 1910 (not some sprightly impact on one’s sensibility), is the idea that imagined visual stimuli reduce a person’s ability to perceive real stimuli. “Having one interferes with the other,” said psychology professor Adam Reeves, who’s been trying to explain the process for more than two decades.

“We have looked at the effects of color, of spatial orientation, of spatial position, of presentation time, and of depth,” he said. “All with an idea as to locating the Perky effect in the visual brain.”

In an article recently published in Frontiers in Psychology, Reeves and his colleague at Elizabethtown College in Pennsylvania add a new twist to the story. “One might expect that increasing the amount of imagery would increase the interference,” said Reeves. “But the opposite happens. Additional elements in the image ‘unmask’ the target, making it visible!”

So, how did they show this? First they had participants imagine four vertical black lines. Then they briefly presented them with an image of two real lines, stacked atop one another and slightly offset. The participants had to keep their imaginary lines in their field of vision and then report whether the lower line was set to the right or to the left of the top line in the real image (what I’ll call “the right/left question”).

When the imaginary lines were very close to the real lines, participants answered the left/right question correctly about 82% of the time. If the imagined lines were far away, they would answer were about 94% accurate.

Next, the team asked participants to imagine eight lines instead of just four and repeated the same experiment. Instead of reducing accuracy even further, the additional elements improved a participant’s ability to correctly answer the right/left question. This time, close imaginary brought participants’ accuracy to 92%.

Prior to these results, Reeves’ team believed that the Perky Effect occurs because of feedback messages coming from the visual cortex (the part of the brain that stores an image) to the geniculate nucleus of the thalamus, the point at which information from the eye first reaches the brain. “The new ‘unmasking’ results challenge this belief,” he said.

Half of the cells in the visual cortex project images forward to the next physiological unit in the brain. But the other half project backwards to earlier stages of input, Reeves said. “So we know from the anatomy that feedback is 50% of everything.” But why this happens is still unclear. “Feedback will be on the research horizon for the next few decades,” said Reeves. “Long after Catherine Lemley and I have retired!”