Performance usually improves with practice, but not if training is arotten time. A new study shows that people's ability to identify noisesdeclines when the sounds are paired with putrid smells–a phenomenon thatmay allow our brain to detect danger more quickly.

In a study published in May in Nature Neuroscience,neurobiologist Rony Paz of the Weizmann Institute of Science in Rehovot,Israel, and his colleagues exposed volunteers to auditory tonespresented with no other stimuli or immediately followed by a rancid orfragrant odor delivered through a nose mask.

After this training session, the subjects were played a series oftone pairs—notes of very similar or identical frequencies—and askedwhether the tones in each pair were the same or different. The subjectsbecame better at distinguishing tones similar to those that had beenpresented alone or with a pleasant scent. But their ability todiscriminate tones resembling those linked to a foul stench worsened–aneffect that persisted one day later.

Such sensory confusion could be an adaptation that allows ourdefenses to rapidly mobilize. "This likely made sense in ourevolutionary past," Paz says. "If you've previously heard the sound of alion attacking, your survival might depend on a similar noise soundingthe same to you."