LONDON: Vision researchers in the US have found that the human brain can keep track of the positions of eight moving objects at once.

The new finding is based on a study wherein the researchers showed volunteers a screen with many moving dots, and indicated which ones the subjects should focus on.

Previous studies had shown that the brain could accurately track the position of up to four dots.

"The magical number was thought to be four," New Scientist magazine quoted Steven Franconeri at Northwestern University in Evanston, Illinois, as saying.

However, Franconeri and his colleague George Alvarez at the Massachusetts Institute of Technology in Cambridge, Massachusetts believe that people can do much better at this task, depending upon the speed at which the dots moved.

A dozen students were recruited for the study, and were asked to track a specific number of the 16 moving dots appearing on the computer screen before them. Unlike in previous experiments, the dots came close to one another but did not touch.

The researchers found that the subjects could accurately follow eight dots over the course of a minute, when the dots on the screen half a metre away moved relatively slowly, about 0.01 metres per second.

Franconeri said that the participants could not keep track of more than eight objects at once, even when they moved at a glacial pace.

"At one point you reach the limit of the number of independent locations you can monitor at once," he said.

As the researchers sped up the movement of the dots on the screen, the number of dots that people could follow dropped precipitously, with the subjects tracking only one dot once when the screen moved at a rate of 0.15 metres per second.

Franconeri believes that the finding that a person can track only one or two objects when they move at high speeds may have implications for the design of video games, and technologies to visualise air traffic control in which people have to follow numerous objects at once.