Study suggests brain handles tasks, perceptions differently

A brain-stumping illusion has a new explanation: Fingers may have a mind of their own.<br><br>When presented with two objects of equal weight but different size, most people think the smaller one is heavier,

Monday, June 26th 2000, 12:00 am

By: News On 6

A brain-stumping illusion has a new explanation: Fingers may have a mind of their own.

When presented with two objects of equal weight but different size, most people think the smaller one is heavier, and nothing can convince them otherwise. Earlier theories blamed the error on a discrepancy between expectation and reality: People expect the smaller object to weigh less, the theory goes, and their surprise at its actual mass adds weight to their mental judgment.

To test this theory, scientists from Queen's University, Ontario, put two boxes of the same weight but different sizes before 40 people. They asked each person to lift each box 20 times, then judge which weighed more. The scientists also measured the force people used for lifting. If the "heavier than expected" theory was correct, people should have used more force to lift the bigger (and seemingly heavier) object.

Instead, though lifters thought the smaller object was heavier after many repetitions, their fingers knew better. By the end of the experiment, people were using the same amount of force to lift boxes of both sizes.

These results suggest, the scientists write in the July issue of the journal Nature Neuroscience, that when the eyes send images to the brain, the brain deals with the information in a different way, depending on whether it is being used to perceive the world or to actually do something.

â€“ Emily Sohn

Feared Ebola infection found to sometimes lack symptoms

The Ebola virus, usually an agent of painful and dramatic death, can also cause a symptomless infection, a new report says.

African and European researchers studied 24 people who did not get sick in recent Ebola outbreaks, despite close contact with victims' body fluids. Ebola is one of the deadliest viruses known, swiftly killing more than 70 percent of those infected. It causes blood-vessel linings to collapse, leading to severe internal and external hemorrhages.

But some people apparently defeat Ebola before it causes damage. Of the 24 people who remained healthy, 11 were infected with the virus, blood tests showed. Researchers could find no genetic mutations in the virus â€“ it was as lethal as ever â€“ but they did find that those with silent infections had a strong immune reaction.

Asymptomatic infection does not appear to contribute to epidemics, the researchers wrote last week in the British journal The Lancet. But they said transmission through semen or donated blood "should be taken into consideration in public health policy."

â€“ Laura Beil

Researchers fear Navy sonar may interfere with whale song

Male whales changed their mating songs when they were exposed to noise from a new U.S. Navy sonar instrument, a new study has found. The National Marine Fisheries Service is investigating whether a similar instrument contributed to six whale deaths in the Bahamas in March.

Biologists from the Woods Hole Oceanographic Institution in Massachusetts recorded the songs of 16 humpback whales before, during and after the instrument was in use. When the sonar was turned on, the songs became longer. When it was shut off, the songs returned to their normal length.

The researchers think the whales may have lengthened their songs to compete with the sonar. The instrument produced one-minute signals of roughly 150 decibels. Worker safety standards for humans allow for 90 decibels (about one one-millionth of the sonar intensity) in an eight-hour period.

In the current issue of the journal Nature, the biologists express concern that changes in the songs might disrupt mating behavior.

The Navy was testing the same type of sonar when six whales with severe ear damage washed ashore in the Bahamas in March. Last month, the National Marine Fisheries Service asked the Navy to thoroughly assess potential environmental damage from the sonar before resuming testing.

â€“ Matthew Carr