Bloodhounds are unlikely to be out of work just yet, but researchers have found humans can track a scent on the ground in the same way that dogs do. While humans are traditionally considered to have a poor sense of smell compared with many of their mammalian cousins, the new finding suggests this reputation may be unfair.
Jess Porter and colleagues first observed that 21 out of 32 participants were able to track a 10 metre trail of chocolate essential oil through an open field using their sense of smell alone. By contrast, none of them were able to track the scent when their nostrils were taped up. (watch film)
Moreover, it seems this latent ability is ripe for improvement through practice. In a second experiment the researchers asked four participants to practise tracking scents for three hours a day, for three days. Afterwards, the participants were more than twice as fast at tracking a scent, and they deviated less from the scent trail. The researchers said such improvements needn’t end there: "Our sense of smell is less keen partly because we put less demand on it", Porter said. "But if people practice sniffing smells, they can get really good at it.”
Next, in a move that opponents of animal experimentation would surely approve of, the researchers used human participants to find out more about how animals track scents. They wanted to know if such tracking is done by comparing odour intensity across the two nostrils, in much the same way that sound is localised by comparing across the ears. Some have argued the nostrils are spaced to close together to be used in this way, but it’s been a difficult issue to research with even in the most well-behaved dogs objecting to their nostrils being blocked.
So 14 human participants attempted to track a scent either with one nostril taped, or with both nostrils clear. Accuracy dropped to 36 per cent with a taped nostril (compared with 66 per cent with both nostrils clear) and speed dropped by 26 per cent. Another experiment used a special device that combined airflow so that both nostrils received the same information, and this was again found to impair performance.
“Here we find that mammals performing a scent-tracking task, freely able to move their nose and sample the olfactory environment in real time, reap added benefit from sampling via their two spatially offset nostrils”, the researchers concluded.
Porter, J., Craven, B., Khan, R.M., Chang, S-J., Kang, I., Judkewicz, B., Volpe, J., Settles, G. & Sobel, N. (2006). Mechanisms of scent tracking in humans. Nature Neuroscience, 10, 27-29.
Link to film showing human tracking scent.