首页 >> 小红猪作品 >> 文章

原文链接

Birds, rats and even hamsters are able to fi nd their way around with consummate ease. So how come we can’t navigate our way out of a paper bag? Chris Berdik gets his compass out...

clip_image002

THE journey seemed simple enough, on the map anyway. Allison Fine left her home to drive to Vermont, just a few hours north on a major highway. She had studied the route and had a GPS gadget to help her. Nevertheless, she soon had absolutely no idea where she was.

"I don't know what happened," she says, "but I pulled over in tears, called my husband and said, 'find me on Google Maps and talk me to Vermont'." This he did, staying on the line for more than an hour.

Fine is an extreme case, but the feeling of getting hopelessly lost is something that most of us can relate to. In fact, along with our flair for language and our unparalleled intelligence, less-than-stellar navigational skills are among the things that can be considered uniquely human. While the vast majority of animals have no trouble finding their way around, most people, when stripped of maps or signs, are notoriously bad at it. A handful are so terrible at orienting themselves, even in places they know well, that they rarely leave the house alone (see "Lost in space"). "I try to study maps," says Fine. "But when I get out into the real world, it just looks completely different."

Until recently, little was known about how the human inner compass works. This is partly because "sense of direction" is not one neatly defined ability. Instead, it is made up of many different skills, such as awareness and memory of your surroundings, sensing your speed and direction changes over time, and tracking the location of objects and places relative to you as you move through an environment. These skills rely on many different parts of the brain, including those involved in vision, memory and imagination, which are tied together into a "cognitive map" by the hippocampus.

Now researchers have begun to unravel how this system works, and to ponder whether we have lost our way somewhere in evolution, or whether our inner homing pigeon is simply lying dormant, waiting to be released.

The first person to explore the idea of a cognitive map - a mental representation of an individual's physical surroundings - was Edward Tolman, a psychologist at the University of California, Berkeley, in 1948. Tolman observed that rats could take novel routes to food hidden in a maze when their learned route was blocked or they were moved to a new starting point. Since then, countless other species have shown an impressive talent for keeping track of where they are.

Take golden hamsters. They can make a straight dash for home even after being blindfolded and led in a winding path away from their nests. Similar skills have also been observed in geese, toads and spiders.

Equivalent tests with people, however, have seen our species come up seriously short. In "triangle completion" tasks, researchers lead people, either blindfolded or in a landmark-free virtual-reality environment, along two sides of a triangle and then tell them to find their way back to the starting point. In one such study, Jack Loomis, a cognitive psychologist at the University of California, Santa Barbara, found that the average error on the final turn was 24 degrees and most people significantly under or overshot the distance. As Loomis summed up: "None of the subjects exhibited good performance."

This weak innate ability to judge distance and direction makes for some pretty squishy mental maps, says William Warren, a cognitive neuroscientist at Brown University in Providence, Rhode Island. He fitted volunteers with virtual-reality headsets and showed them how to navigate virtual mazes. In half of the experiments, the mazes contained virtual, and invisible, "wormholes" that transported subjects close to a target that they would have known was some distance and a turn or two away. Yet the volunteers happily passed through these shortcuts to end up at a point that even a halfway-decent geometric reckoning would have told them was impossible. "The punchline," Warren says, "is that people didn't even notice anything amiss."

These findings, presented at this year's Vision Science Society conference in Naples, Florida, suggest that human cognitive maps pay little heed to geometric realities. Instead, we remember webs of landmarks such as the store, our office, the church where we turn left on our way home, yet have little sense of how these fit together spatially.

Of course, some species find their way with the aid of specialised senses that we simply do not possess. Migratory birds can sense the Earth's magnetic field, for example, while some insects can see gradations in the polarity of sunlight. Yet even animals that lack any huge sensory advantage, such as hamsters, navigate better than many of us.

In a series of recent studies, Michael Kahana and his colleagues at the University of Pennsylvania in Philadelphia studied the brains of epileptic people, who already had electrodes implanted in their brains, as they played a taxi-driving video game. By noting which neurons fired when, the researchers discovered that human brains have specialised neurons dedicated to sense of direction, similar to those found in the hippocampus of rats, mice, monkeys and goldfish. So why can't we compute geometric space in the same way?

Losing our way

It could be that we lost this ability at some point in our evolution, sacrificing the kind of precision that other animals enjoy in return for cognitive flexibility, which allows us to make sense of our surroundings and find our way using reasoning and experience rather than geometry.

Indeed, studies of people that live closest to the land, such as the Bedouin in the Sahara, Arctic Inuit and Australian Aborigines, show that reasoning and experience can be very useful for finding your way. Such people can navigate perfectly well using subtle, learned directional cues from the landscape, even in what looks like the most barren expanse of snow or desert. Trading a mental tally of distance and direction for real understanding of the landscape in this way may have given us an evolutionary boost.

The trouble is, unlike an innate computation of distance and directional change, this connection to the landscape is all too easy to distort or lose entirely. Claudio Aporta, an anthropologist at Carleton University in Ottawa, Ontario, Canada, has observed how young Inuit hunters, who have begun to rely on GPS to navigate, have found themselves hopelessly lost for days when the technology fails, leading to several fatal and near-fatal incidents (Current Anthropology, vol 46, p 729). This was unheard of among the elders - until recently, the Inuit didn't even have a term for being lost. "It was just a matter of time before the weather cleared or they recognised a feature on the land and they would find their way," says Aporta.

That these skills are so easily lost could explain why the average westerner struggles to navigate without help. Most people now live in a world that has been made navigable by maps, street signs, transport networks and GPS. There is no need to understand the environment to get around.

Yet while these findings seem to show that we could all navigate like a Bedouin if we had to, other studies indicate that for some of us, substantial improvements may be impossible.

In 2006, Daniel Montello and Toru Ishikawa at the University of California, Santa Barbara, taught 24 people two landmark-studded routes which were connected by a winding but landmark-free route in 10 weekly sessions. After each session, they asked participants to point from one landmark to the others, which were always out of sight, and draw maps of the routes.

Three clear groups emerged: one that kept doing well throughout the experiment, one that did poorly from beginning to end and one that was intermediate. This final group was the largest, and the volunteers within it all improved at the tasks as the experiment progressed, although only one-third of this group became as good as the top performers (Cognitive Psychology, vol 52, p 93).

To Thomas Wolbers, a neuroscientist at the University of Edinburgh, UK, findings like these point to a genetic component to navigation ability. Several studies have found signs of such a link in rodents, and Wolbers is currently looking for similar evidence in a sample of 50,000 people. He expects to get initial findings in about a year.

Regardless of whether all or just some of us are a navigational lost cause, psychologist Colin Ellard at the University of Waterloo in Ontario, author of You Are Here, argues that there is an upside to our lack of natural navigation skills. He suggests that losing our relationship with physical space, coupled with the unique human ability to imagine ourselves in another location, may have given us the freedom to create a reality of our own. What other species could comprehend the World Wide Web or contemplate exploring new worlds, he asks.

And while we may strug