Scientists seem to think that, if told to picture an elephant, you will always, on some level, obediently picture an elephant. But asking people to picture a pink elephant is a different matter... maybe. How much control you have over your own thoughts?
For Want of a Nail
Everyone likes to think they have an independent mind and a high level of willpower, and will be reluctant to admit that they can be forced to picture something in their mind just because someone said a group of words, like, "Picture an elephant." Psychologists, therefore, have to take special measures to see if people picture words in their head just because the words are said.
Psychologist Rolf Zwaan decided to test the idea by seeing how fast people respond to visual cues after hearing certain words. He accomplished this by doing an end run around asking people if they saw the object itself, and instead asked them about the orientation of the object. He had the subjects read a few sentences about a carpenter hammering a nail; sometimes the carpenter was hammering the nail into the floor, and sometimes into the wall. The subjects were then asked to look at a picture of an object and press a button if the object was in the story. The people who read the story about the carpenter hammering the nail into the floor responded faster if they saw a picture of a nail oriented vertically, the way it would be oriented if someone were hammering it into the floor. The people who read the story about the nail being pounded into the wall responded faster if they saw the nail oriented horizontally. They recognized what they had been picturing, even if they didn't know they had pictured it.
The Shape of an Eagle and the Color of a Steak
Other experiments sprang from this basic model. Zwaan himself branched out by seeing if people would respond to more than just the orientation of an object. He found an especially strong response when he tested for shape. Shape, in this case, isn't a basic circle or square, but the shape an object takes when it's performing some action.
The experiment followed the same form as the previous experiment, but changed objects. For example, people were asked to identify a picture of an eagle after they had read a story about an eagle. If, in the story, the eagle was soaring, they were quicker to recognize the eagle if it had its wings outspread than if it were standing with its wings folded. People who read about an eagle on its nest were faster on the draw when they saw the eagle with its wings folded than they were when its wings were outspread. An image that matches what people have in their head is recognized faster than an image that doesn't.
...except for one experiment, in which people read about a steak in a butcher shop window. They were quicker to recognize a steak that was dark brown than a steak that was colored red. As butchers are not known for cooking their steaks beforehand, it's possible that we don't imagine color, even when we see descriptions that indicate color.
Pink Elephants on Parade
But before you think your brain is free of the insidious control of language, consider a more recent experiment. The framers of the experiment recruited people on the internet, and had them review stories and press buttons when they recognized the image described in the story. Again, shape was a major factor in people's reaction time. Orientation was pretty much neutral.
In this case, though, matching the color of the real image with the color of the object in the story did shrink people's reaction time significantly. People, according to this experiment, do picture color in their head when they read about an image. What was the difference between the results in this study and the results in the steak study? The study authors speculated that people only really noted significant colors. Perhaps people don't find the color of a steak significant. Dripping red or well-browned, it's going in their belly eventually. The color of a traffic light, or a murder suspect's car is more likely to stick in their head.
So can you be forced to picture a pink elephant? It depends. If it's important to you that the elephant is pink, then you probably will think about it in its pinkness. If, however, you find no significance in the elephant's color, you can keep your mind off of it.