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THIS WEEK
Mystery of the exploding continent Jeff Hecht
WAS there a Stone Age apocalypse or not? One theory has it that about 13,000 years ago a comet blasted North America, wiping out the continent’s megafauna – as well as its early settlers. It’s a compelling story that offers a simple explanation to the mystery of why mammoths, mastodons, and Clovis humans disappeared. But it’s highly
Their breath on your skin helps you hear DEPENDING on whose it is, breath on your neck may or may not feel good. Either way, now it seems that it can help you understand what someone is saying. The discovery could lead to hearing aids that emit puffs of air. We know that what we see affects what we hear. For example, if we hear “ba” while watching a person saying “ga” we think we’ve heard “da”. Bryan 16 | NewScientist | 28 November 2009
controversial, and new research suggests the impact was far too small to have done any serious damage. Doubts spring from the speed of extinctions, the fate of the Clovis culture and the presence, or lack, of supposed impact signatures. Advocates of the comet-blast theory say they will present new data at the American Geophysical Union (AGU) meeting in San Francisco,
Gick and colleagues at the University of British Columbia in Vancouver, Canada, wondered whether tactile sensations affect hearing too. In speech, the “aspirated” syllables “pa” and “ta” are accompanied by a puff of exhaled air, whereas “ba” and “da” are not. Such puffs aren’t always detected when someone is speaking, but Gick’s team reasoned that the brain might learn to use puffs to modify its perception of certain sounds. They had 66 volunteers listen to a male voice saying all four syllables against background noise that made it hard to distinguish them. At the
steadily between 14,800 and 13,700 years ago, making them rare 800 years before any comet strike. Williams says the work rules out a sudden, impact-driven extinction (Science, DOI: 10.1126/ science.1179504). However, geologist and impactadvocate James Kennett at the University of California, Santa Barbara, calls that “a classic case of over-interpretation” because the data came from only a small area rather than from different sites across the whole of North America. Some anthropologists are also unhappy with the suddenextinction theory, taking issue with claims that an impact wiped –Blasted out of existence?– out the Clovis people. It’s true that distinctive Cloviswhere they will share the stage style artefacts disappear at the with sceptics. start of a dramatic cooling event “Nothing special happened which began about 13,000 years 12,900 years ago,” says John ago, called the Younger Dryas. Williams at the University of But the people didn’t die out, Wisconsin-Madison. His data says Vance Holliday at the suggest that large mammals University of Arizona in Tucson. were already rare well before “An artefact style was replaced the purported blast. Williams by another style. You see that all and his colleagues searched over the world.” layered lake-bottom deposits Some Younger Dryas deposits in Indiana and New York State do contain residues similar to for the spores of the fungus those from the 1908 Tunguska Sporormiella found in the dung explosion over Siberia, says of large plant-eating mammals Adrian Melott of the University such as mammoths (pictured) of Kansas, Lawrence. He reckons and horses. there was a North American From a decline in the spore impact but that it was only counts, they conclude that the one-hundredth the scale of megafauna population dropped the proposed comet blast. ■
same time as some of the syllables, they delivered a puff of air to the hand or neck. Although many volunteers could not consciously feel the puffs, they were still more successful at correctly identifying “pa” and “ta” when these sounds were accompanied by air puffs. In contrast, air puffs made it less likely that they would correctly identify “ba” and “da” and more likely
“Hearing aids and headsets could be fitted with pneumatic devices that emit puffs of air”
that they would mistake these for sounds for “pa” and “ta” (Nature, DOI: 10.1038/nature08572). Gick says that we likely use puffs of air to make sense of speech. “It gets integrated into a single event in your mind,” he says. He envisions hearing aids or headsets fitted with devices that emit puffs of air when they detect an aspirated sound. These might help pilots struggling to make out communications in a noisy plane, he says. But John Foxe at the City University of New York says it is not clear that puffs would work “in realworld conditions”. Aria Pearson ■
THIS WEEK
Mystery of the exploding continent Jeff Hecht
WAS there a Stone Age apocalypse or not? One theory has it that about 13,000 years ago a comet blasted North America, wiping out the continent’s megafauna – as well as its early settlers. It’s a compelling story that offers a simple explanation to the mystery of why mammoths, mastodons, and Clovis humans disappeared. But it’s highly
Their breath on your skin helps you hear DEPENDING on whose it is, breath on your neck may or may not feel good. Either way, now it seems that it can help you understand what someone is saying. The discovery could lead to hearing aids that emit puffs of air. We know that what we see affects what we hear. For example, if we hear “ba” while watching a person saying “ga” we think we’ve heard “da”. Bryan 16 | NewScientist | 28 November 2009
controversial, and new research suggests the impact was far too small to have done any serious damage. Doubts spring from the speed of extinctions, the fate of the Clovis culture and the presence, or lack, of supposed impact signatures. Advocates of the comet-blast theory say they will present new data at the American Geophysical Union (AGU) meeting in San Francisco,
Gick and colleagues at the University of British Columbia in Vancouver, Canada, wondered whether tactile sensations affect hearing too. In speech, the “aspirated” syllables “pa” and “ta” are accompanied by a puff of exhaled air, whereas “ba” and “da” are not. Such puffs aren’t always detected when someone is speaking, but Gick’s team reasoned that the brain might learn to use puffs to modify its perception of certain sounds. They had 66 volunteers listen to a male voice saying all four syllables against background noise that made it hard to distinguish them. At the
steadily between 14,800 and 13,700 years ago, making them rare 800 years before any comet strike. Williams says the work rules out a sudden, impact-driven extinction (Science, DOI: 10.1126/ science.1179504). However, geologist and impactadvocate James Kennett at the University of California, Santa Barbara, calls that “a classic case of over-interpretation” because the data came from only a small area rather than from different sites across the whole of North America. Some anthropologists are also unhappy with the suddenextinction theory, taking issue with claims that an impact wiped –Blasted out of existence?– out the Clovis people. It’s true that distinctive Cloviswhere they will share the stage style artefacts disappear at the with sceptics. start of a dramatic cooling event “Nothing special happened which began about 13,000 years 12,900 years ago,” says John ago, called the Younger Dryas. Williams at the University of But the people didn’t die out, Wisconsin-Madison. His data says Vance Holliday at the suggest that large mammals University of Arizona in Tucson. were already rare well before “An artefact style was replaced the purported blast. Williams by another style. You see that all and his colleagues searched over the world.” layered lake-bottom deposits Some Younger Dryas deposits in Indiana and New York State do contain residues similar to for the spores of the fungus those from the 1908 Tunguska Sporormiella found in the dung explosion over Siberia, says of large plant-eating mammals Adrian Melott of the University such as mammoths (pictured) of Kansas, Lawrence. He reckons and horses. there was a North American From a decline in the spore impact but that it was only counts, they conclude that the one-hundredth the scale of megafauna population dropped the proposed comet blast. ■
same time as some of the syllables, they delivered a puff of air to the hand or neck. Although many volunteers could not consciously feel the puffs, they were still more successful at correctly identifying “pa” and “ta” when these sounds were accompanied by air puffs. In contrast, air puffs made it less likely that they would correctly identify “ba” and “da” and more likely
“Hearing aids and headsets could be fitted with pneumatic devices that emit puffs of air”
that they would mistake these for sounds for “pa” and “ta” (Nature, DOI: 10.1038/nature08572). Gick says that we likely use puffs of air to make sense of speech. “It gets integrated into a single event in your mind,” he says. He envisions hearing aids or headsets fitted with devices that emit puffs of air when they detect an aspirated sound. These might help pilots struggling to make out communications in a noisy plane, he says. But John Foxe at the City University of New York says it is not clear that puffs would work “in realworld conditions”. Aria Pearson ■