Good movies change people’s view of the world all the time, but how many can say a movie has fundamentally altered their vision forever? One person who can is Bruce Bridgeman. In terms of how he sees the world, there is life before Hugo, and life after Hugo.
On 16 February this year, Bridgeman went to the theatre with his wife to see Martin Scorsese’s 3D family adventure. Like everyone else, he paid a surcharge for a pair of glasses, despite thinking they would be a complete waste of money. Bridgeman, a 67-year-old neuroscientist at the University of California in Santa Cruz, grew up nearly stereoblind, that is, without true perception of depth. “When we’d go out and people would look up and start discussing some bird in the tree, I would still be looking for the bird when they were finished,” he says. “For everybody else, the bird jumped out. But to me, it was just part of the background.”
All that changed when the lights went down and the previews finished. Almost as soon as he began to watch the film, the characters leapt from the screen in a way he had never experienced. “It was just literally like a whole new dimension of sight. Exciting,” says Bridgeman.
But this wasn’t just movie magic. When he stepped out of the cinema, the world looked different. For the first time, Bridgeman saw a lamppost standing out from the background. Trees, cars and people looked more alive and more vivid than ever. And, remarkably, he’s seen the world in 3D ever since that day. “Riding to work on my bike, I look into a forest beside the road and see a riot of depth, every tree standing out from all the others,” he says. Something had happened. Some part of his brain had awakened.
Conventional wisdom says that what happened to Bridgeman is impossible. Like many of the 5-10% of the population living with stereoblindness, he was resigned to seeing a world without depth. What Bridgeman experienced in the theatre has been observed in clinics previously – the most famous case being Sue Barry, or “Stereo Sue”, who according to the author and neurologist Oliver Sacks first experienced stereovision while she was undergoing vision therapy. Her visual epiphany came during the course of professional therapy in her late-forties. The question is why after several decades of living in a flat, two-dimensional world did Bridgeman’s brain spontaneously begin to process 3D images?
For centuries, scientists have known that two eyes are better than one. The Roman physician Galen observed that images received by the two eyes are slightly different, as did Leonardo Da Vinci many centuries later. Open your left eye only and then switch to the right eye only and you’ll see how: the image looks the same but it has moved a little.
In the 1830s, the English scientist and inventor Charles Wheatstone discovered why: the differences between the two images allow the brain to generate a sensation of depth. He even designed ingenious devices called stereoscopes, in which two slightly different versions of the same image viewed together through the instrument transformed into a single three-dimensional drawing.
Somehow the brain fuses these images automatically, and it’s only in the last few decades that we have begun to understand the nerve signals underlying this stereovision. In much the same way that different cells in the tongue respond to different types of taste – bitter, sweet, salty and sour – so too there are cells in the eye and brain that respond to only one type of signal, for example, vertical or horizontal lines. The farther this signal travels into the brain, the more complex it becomes.