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据每日健康新闻报报道，最新的嗅觉研究显示，常人的嗅觉在开阔地形对地面气味的敏感度，比大多数人所认为的要更为敏感。

这项由美国和以色列合作完成的研究，12月17日发表于网络版的《自然·神经科学》杂志。一般认为人的嗅觉灵敏度较差，但该研究发现人们确实能在某个空间环境下准确地靠嗅觉找到路-- 虽然成功率较少，加上如果他们一边鼻子不通的话，花费时间也比较长。该研究报告同时指出，事实上，人通过受训后，就可单纯地依靠嗅探地面气味来确保自己在不熟悉的地方也能对其方位了解得一清二楚。实际上，人们会本能地模仿某些动物的行为，包括单独使用每个鼻孔鉴别一些清楚的气味，然后再利用三角定位定出一条道路。

研究人员共开展了5项试验，目的在于评价人们跟踪气味的嗅觉能力。 试验地点选择在一个空旷地带，受试的男女对象被随机抽取参加这5项试验，最少一次是4人，最多多达32人。

试验1：受试者事先都被蒙眼以及塞住耳朵，之后就被要求沿着一条10米长的散发着“巧克力香精油”芬芳的路线行走。说是行走，其实是扮成“骑马打仗”的“马”，用戴着厚重手套的手和膝部爬行，并且鼻子紧贴地面，就这样闻香而行。3 分之2的受试者在这一测试中都没有偏离路线。 不过，当他们的两边鼻子被堵上，什么都闻不到时，每一个都偏离了路线。

试验2：为了验证“熟能生巧”的说法，研究人员随后对两男两女进行了训练，一天3次完成相同的路线行走，一连三天，为期两周。结果发现这类训练使得受试者能更快更准确地嗅探跟踪香精油路线。实际上，短短几天内，他们嗅探气味的速度就加快了一倍。研究人员认为训练越多，嗅探的效率就会越高。同时也发现，随着嗅探跟踪气味速度的提高，鼻子吸气的频率也也越快。研究人员指出，在吸气频率方面，狗要比人快得多，它们极为灵敏的嗅觉或许就是拜此所赐。

试验3：试验结果显示，人的两个鼻孔各自吸入不同的气味，这些气味来自于鼻子两边互不重叠的气体空间。研究人员指出，之前的研究显示，在空旷地带飘浮的气味通常就只固定于如此小范围的气体空间，以致于只有一侧的鼻孔才闻得到，而另一个则闻不到。

试验4：基于这一发现，研究人员在此试验中将受试者一侧的鼻孔堵起来，随后叫他们完成“闻香识路”测试。结果显示，单个鼻孔嗅探跟踪气味的准确率明显下降，比较于双鼻孔正常嗅探测试，为36％ 对66％，速度方面，则下降了26％。

试验5：研究人员使用了一种特殊的面罩。这种面罩不会妨碍两个鼻孔的呼吸，但是会迫使吸进来的空气在被吸入鼻子以前混在一起，形成单股的气流。研究人员发现这种方法形成的“统一鼻孔”，其嗅探速度比双鼻孔正常嗅探测试下降了24％，准确率也有显著下降。

这表明，人类的最佳嗅觉需要各个鼻孔分工俱细的合作，如此方能更好地辨别气味，要知道造物主造人可不是胡捏乱造，每个器官都是有其职所司的。研究人员最后对其研究下结论道：诚如我们在动物身上所看到的，人类的嗅觉能力同样能被加以善用从而发挥出强大作用。

对许多人来说，眼睛仍然是一扇重要的沟通世界的窗口。人类高度依赖视觉，而栖息于黑暗环境中的动物则主要依赖嗅觉。在我们的视觉和听觉变得如此敏锐的时候，我们的一些嗅觉能力却在丧失。不过这也许是我们对自己的嗅觉都有点爱理不理吧，其实嗅觉的作用机制所能产生的作用比我们所了解的恐怕要大得多。而且，如果我们刻意训练提升自己的嗅觉灵敏度，那么我们的空间方向感将得到很大改善。

在这方面，一位人体气味化学方面的专家也有同样看法。他说，人类的嗅觉天赋能通过后天开发能够变得越发灵敏。我们的嗅觉可能不象狗或者啮齿动物一样好，但是当我们用之得当时，它仍然相当敏锐。那些以嗅觉谋生的人，象是香水闻香师，就是把嗅觉用对地方了，而且闻香工作使他们的嗅觉会有意识地对香水味表现得更为敏感。

嗅觉在我们的日常生活中很重要，我们经常使用它，不仅用来评品佳肴，而且用来“嗅”出周围人对我们的看法。因此，我们人类的鼻子超乎想象地灵敏。

Human Sense of Smell Nothing to Sniff At
12.18.06, 12:00 AM ET

MONDAY, Dec. 18 (HealthDay News) -- Lost in the dark, without sight, sound, or clue? Follow your nose.

New olfactory research suggests that when it comes to tracking scent at ground-level on open terrain, the average human's sense of smell is stronger than most people believe.

"There's this general assumption that people have a bad sense of smell," said study lead author Jess Porter, a Ph.D. candidate in biophysics at the University of California at Berkeley. "But we found that people can certainly sniff their way accurately around a spatial context -- although less successfully and slower if they have only one nostril to work with."

The new American-Israeli study, published online Dec. 17 in Nature Neuroscience, reports that people can, in fact, be trained to rely exclusively on ground-level smelling to successfully navigate unknown territory. In fact, they instinctively mimic certain animal behaviors, including enlisting each nostril to independently identify distinct smells and "triangulate" a path.

Porter joined Berkeley psychology professor Noam Sobel and a team of colleagues. Together, they conducted five experiments aimed at assessing people's ability to track scents.

Enlisting anywhere from four to 32 male and female participants for the various tests, the researchers worked in an open field.

The subjects were first blindfolded and ear-plugged before being asked to follow a 10-meter trail scented with "chocolate essential oil." They followed the trial by moving close to the ground on their hands and knees and wearing thick gloves, with only their noses to guide them.

Two-thirds of the participants were able to do so. However, when their noses were plugged to cut off the ability to smell, none of them could follow the path.

To test if "practice makes perfect," two men and two women were subsequently trained to complete the same task three times a day for three days, stretched over a two-week period.

Porter and her team found that this type of training allowed subjects to track scent trails faster and with greater accuracy. In fact, their speed of execution doubled within a few days. The researchers believe more training might boost efficiency even higher.

Porter's group also found that as the speed of trained scent tracking increased, so did sniffing frequency. In this regard, they noted that dogs sniff much faster than humans, perhaps accounting for their superior tracking abilities.

A third experiment revealed that each of a person's two nostrils inhales distinct smells, pulled from non-overlapping regions in the air. The researchers pointed out that prior studies have shown that scent "plumes" in the open are often confined to such small areas that only one nostril will pick it up, while the other will not.

The fourth test followed up on this finding by asking 14 subjects to complete the field-tracking experiment, but with one nostril taped shut.

Single-nostril tracking was much less accurate (36 percent versus 66 percent) and 26 percent slower compared to using both nostrils.

Finally, the authors conducted a final test using a special mask that allowed both nostrils to inhale, but forced incoming air to join together into a single air stream inside the middle of the nose.

Porter and her associates found that this "unified nostril" method was 24 percent slower and much less accurate than tracking completed normally.

This shows that optimal human tracking requires the individual use of each nostril to better distinguish smells as people home in on an appropriate route.

The team concluded that, just as happens with animals, people's capacity to smell can be harnessed to great effect.

Still, for most people, eyes remain the key window on the world.

"I think it's fair to say that humans are very, very visual, whereas an animal that lives in the dark is primarily olfactory," noted Porter. "And people do have this idea that as our sense of vision and hearing has become so prominent, we've lost some of our olfactory capability."

That might not be the full story, however. "We think it's maybe that we don't place an emphasis on our sense of smell," Porter suggested. "Because the underlying mechanisms are still there -- to a greater extent than we maybe notice them. And if we place demands on them and train ourselves, our ability to follow a spatial path can improve a lot."

George Preti, a member of Monell Chemical Senses Center in Philadelphia, a research institute devoted the science of taste and smell, agreed that humans' olfactory talents can be honed with practice.

"Our sense of smell may not be as good as dogs or rodents, but it's still pretty acute when we use it correctly," he said. "I'm an expert in the chemistry of human odors, and I can tell you that folks that use it for a living, like perfumers, do improve their use of it and make themselves more consciously sensitive to that kind of input."

"Smell is important in our everyday life," Preti added. "And we use it a lot. Not just for evaluating food, but also for how we're perceived by the rest of the world. So, I'd say that humans certainly do have very sensitive noses -- regardless of what people might think."

http://www.forbes.com/forbeslife/health/feeds/hscout/2006/12/18/hscout600212.html

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