Old people have a reputation for producing a distinct stink that follows them around like, well, a bad odor. Now, chemo-sensory experts have found that people can indeed pick out the aged aroma -- and it's actually more pleasant and less intense than body odors from twentysomethings and middle-age folk.
The new study, published by the journal PLoS ONE, provides the first look at humans' ability to gauge age on the basis of smell -- even when they aren't aware of it. The inspiration came from a childhood memory, said Johan Lundstrom, a neuropsychologist at the Monell Chemical Senses Center in Philadelphia. Lundstrom's mother worked at a retirement home in Sweden, and as a boy he would visit. While giving a talk at a retirement home in Philadelphia, he was struck by the smell, which he said, "was identical ... two different continents, two different populations, but similar odor."
To see if this phenomenon held up in the lab, researchers asked 41 volunteers between ages 20 and 95 to spend five nights sleeping in T-shirts with nursing pads sewn into the armpits. A different group was asked to assess the odors in the jars, rating them according to intensity and pleasantness (or unpleasantness).
It turned out that the underarm odor of 75- to 95-year-olds was judged to be less intense and far more pleasant than the scent of either young or middle-age adults. The most intense -- and perhaps not coincidentally, the most unpleasant - odor came from 45-to-55-year-old men. Women in that age group, on the other hand, produced the most pleasant smell of everyone. On the whole, men generally smelled worse than women, but that distinction disappeared in old age -- likely because men's hormone levels change as they age, the researchers found.
Lundstrom said: "As you grow older, you smell more and more like a woman."
Infants are constantly trying to make sense of the world around them, and they do this by seeking out situations that are neither too simple nor too complex. Writing in the journal PLoS One, a team of researchers from the University of Rochester call it the "Goldilocks effect."
Babies "are seeking out the type of learning material from the world that's most efficient for them to learn from," said the study's lead author, Celeste Kidd, a cognitive scientist at the university.
Her team measured the attention patterns of 72 infants, ages 7 and 8 months, as they watched video animations while an eye-tracking device below the screen followed their gaze. The babies lost interest when the pattern of objects displayed on the screen became too predictable. And they also lost interest when the sequence became too surprising and random.
The study suggests that infants are much more actively engaged in seeking out information from the world than previously thought, Kidd said. And that means that they do not need fancy toys to learn, she said. A reasonably stimulating environment provides rich possibilities.
"Every parent wants to give their kid the best opportunities possible," she said. "But the child is playing with whatever is in front of them; they're doing the best with it they can."