One day in 2005, a retired building surveyor in Edinburgh visited his doctor with a strange complaint: His mind’s eye had suddenly gone blind.
The surveyor, referred to as MX by his doctors, was 65 at the time. He had always felt that he possessed an exceptional talent for picturing things in his mind. The skill had come in handy in his job, allowing MX to recall the fine details of the buildings he surveyed. Just before drifting off to sleep, he enjoyed running through recent events as if he were watching a movie. He could picture his family, his friends, and even characters in the books he read.
Then these images all vanished. The change happened shortly after MX went to a hospital to have his blocked coronary arteries treated. As a cardiologist snaked a tube into the arteries and cleared out the obstructions, MX felt a “reverberation” in his head and a tingling in his left arm. He didn’t think to mention it to his doctors at the time. But four days later he realized that when he closed his eyes, all was darkness.
Worried, MX paid a visit to Adam Zeman, a neurologist at the Peninsula Medical School in Exeter, England. Zeman was so intrigued by the case that he teamed up with Sergio Della Sala, a cognitive neuroscientist at the University of Edinburgh who specializes in how the brain handles visual information. Neither Zeman nor Della Sala could offer MX a cure for his condition, unfortunately, but they recognized a rare chance to study how the mind’s eye works. Della Sala proposed running a series of exams. MX gave his consent.
Scientists have long speculated that the act of seeing things in our mind’s eye employs some of the same brain circuits that we use when seeing with our physical eyes. A number of brain scan studies have supported this view. When you look at a person up close, for example, a particular network of brain regions becomes active, including areas that process raw signals from your eyes as well as more sophisticated regions that recognize individual faces. When you close your eyes and conjure up a face, the parts of the brain that receive signals from the eyes are dormant, but the regions that recognize the features defining an individual again light up.
MX gave Della Sala and Zeman the chance to test two ideas about the role of the mind’s eye in our inner life. Some scientists have argued that the mind’s eye is constantly at work whenever we look at our internal simulations of the world. Stephen Kosslyn, a Harvard psychologist, goes so far as to argue that we rely on the mind’s eye to make decisions about what we should do in the future. When we start driving home from a friend’s house, for example, we envision the different routes we can take in order to decide on the best way to go.
Kosslyn has his critics, though. Zenon Pylyshyn, a cognitive scientist at Rutgers University, doesn’t think mental images are essential to figuring such things out. We all have the experience of picturing things in our heads, of course. If someone asks you how many paws are on a cat, you may see the image of a cat in your mind and count the paws. But the experience of using your mind’s eye doesn’t fully explain the mental processing that goes on beneath the surface. There may be other, more essential computations that lead you to your conclusion.
To test these competing interpretations, Della Sala and Zeman put MX through a battery of tests. First they wanted to find out whether the problem with his mind’s eye was just one part of a greater disorder. They tested his other faculties, such as his ability to make decisions and form memories. To see just how unusual MX was, the scientists decided to assemble a group of control subjects who were similar to him except for his complaint, so they recruited 10 male architects around the age of 60.
The tests revealed that MX was, for the most part, pretty much like the other men. He had a high IQ and a reliable memory. He did an excellent job at playing a card-swapping game in which the rules could change unexpectedly. His vision was normal, and he could easily put names to the faces of famous people shown to him. In other words, the vision-processing networks in his brain and his memory systems were in good working order.
When the scientists tested the mind’s eye of MX, though, the difference was stark. The researchers gave all their subjects a standardized test called the Vividness of Visual Imagery Questionnaire. They asked each participant to picture things like a landscape and a friend. Then the scientists had each man rate the image that came to mind. If it was as vivid as normal vision, he was asked to score it a 5. If there was no mental image at all—if the subject knew only that he was thinking of an object—he was to give it a score of 1. Most of the men scored high on the test. MX scored as low as possible, racking up a bunch of 1s.
Della Sala and Zeman scanned MX’s brain to see if they could find the source of this deficit. They first showed him a series of faces. MX’s brain responded in much the same way as the architects’ brains did, activating a network of regions that process vision and recognize individuals. Then the scientists showed their test subjects a series of names of famous people. As they read each name, the men were asked to picture that person. In the brains of the control group, the mind’s-eye regions became active, much as before. But in MX’s brain, those regions remained quiet. Even though the individual regions of his brain were working normally, some of the connections seemed to be down.