Ever heard of the Perky Effect? It sounds cutesy-poo, but it's an effect that has led to a decades-long investigation that reveals a startling truth. Even if you don't consciously control your dreams, you probably think you control your daydreams. But that might not actually be true.

C.W. Perky and the Color Yellow

C.W. Perky is not as famous as she should be. If she had made her discovery a little more recently than 1910, she might have had more power in the lab in which she worked, and had more chances to promote her work and follow up on her findings. At it is, she would perhaps be pleased to learn that "The Banana Effect" was re-named "The Perky Effect."


The Perky Effect was discovered using nothing more complicated than a wall, a projector, and a very faint color slide. Or maybe that's not true. It also required a human brain, properly focused. Perky recruited subjects, and brought them in to stare at the blank wall. To give them something to pass the time, she asked them to picture certain objects. Perky didn't try to tax the subjects' imaginations. The objects to be mentally pictured included a tomato, a leaf, a lemon, and a banana. While the people spent their time envisioning produce, Perky slowly turned up the projector. A faint, rough image came up on the screen. If the subject had been asked to picture a tomato, the image would be of a faint red roundness. If the subject had been asked to picture a banana, the image would be an oblong curve.

All of the images were strong enough to be seen. When a subject was placed in front of the wall and not told to picture a leaf or a banana, they saw the faint color right away. The people who were picturing the bananas never did. Except that, yes, they actually did see it. After the experiment, each subject was asked to describe what the fruit that they had been picturing. A subject who was shown an image of a yellow curve oriented like the smile on a smiley face had pictured the banana on its side and curved up. A subject who was shown a yellow curve oriented like one side of a parentheses had pictured the banana in a vertical position.


Scientists Can Keep You From Seeing Things

There are two types of phenomena demonstrated by this experiment — and psychologists were eager to explore both. The first one showed that, by asking people to picture something in their heads, researchers could render them - to a certain extent - blind. Over the next few decades, scientists spent time seeing what they could do to enhance the effect.

To start with, the subject had to be relaxed. At first, when people tried to recreate Perky's experiments, their subjects saw the image right away. It took time to get people into the right frame of mind for daydreaming. The imagery that scientists requested their subjects dream up also controlled the intensity of the effect. Familiar objects that people had stored in long-term memory, like common fruits or household products, worked very well. More complicated and unfamiliar shapes didn't bring on the effect. People struggling to picture an object remained conscious enough to see the projection, even if the researchers had just recently given them a model of the object to study in preparation for their visualization.


The Perky Effect, scientists found, wasn't limited to vision. Have someone listen to white noise, and ask them to imagine a tone, and they won't be able to hear the tone when it starts up. We can go deaf as well as blind.

Then it was just a matter of fine-tuning. People are less likely to see images if those images appear in front of a "target" object. In other words, if you ask someone to look at a semi-transparent screen while picturing a lemon, and somehow project an image of the lemon (perhaps on a clear window) in front of the screen, the subject isn't likely to see it. Project it behind the screen, and they're much more likely to come out of their reverie. Scientists even started messing with the image while the subjects blindly stared at it. They found that changes in hue aren't detected. Researchers can change the banana-like shape from a neon yellow to a pale pastel, and no one will realize they're seeing anything. Only changing the image's brightness will get the subjects to notice there is anything at all in front of them. So as long as you stay within certain guidelines, you can put an image in front of people and they won't know they're seeing anything.


Scientists Can Make You See

But they are seeing something. This is the second, and less-studied, part of the Perky Effect. The right image can worm its way into a subject's mind and change what they're seeing. Granted, the orientation of a banana isn't exactly Inception, but it is a way to control what people are thinking. The external world makes it into the world of the mind, without the mind ever realizing it.


One study showed that people will sometimes fold images into their reveries even when those images don't fit with what they're picturing. A psychologist tried asking people to picture the New York skyline. While they were thinking about it, she projected the faint image of a tomato on the screen in front of them. Many people saw the New York skyline at sunset. When we see something unusual in our daydreams, we make it work even if we don't know we're seeing it.

[Via Louder Than Words, Journal of Cognitive Science, Visual Imagery Lowers Sensitivity to Hue-Varying, Effects of Imagery on Vernier Acuity, Relaxation and the Perky Effect]