Illustration: Cathy Wilcox
WITH seven wonders of the world, seven deadly sins, and seven days of the week, one could be forgiven for thinking the numeral seven had special significance to humans.
While such groupings may appear more than a coincidence, a Sydney scientist has challenged the long-held wisdom that seven is the ''magical'' number of new things the brain can process at one time.
When people were asked to repeat random list of letters, words or numbers, confusion set in after four, an analysis by University of NSW psychiatry professor Gordon Parker found.
''To remember a seven numeral phone number, say 6458937, we need to break it into four chunks: 64. 58. 93. 7,'' he said.
More than 50 year ago, the American psychologist George Miller published a study that measured people's mental recall of lists of new information.
Dr Miller concluded the brain's short-term memory capacity could absorb roughly seven pieces of information. The study become one of the most cited psychology articles in the world.
But when Professor Parker examined Miller's original data he found the results of his experiments showed the brain could handle only four chunks of information, not seven. Professor Parker believes the popularity of Miller's research came from its evocative title - The Magical Number Seven, Plus or Minus Two. Some Limits on Our Capacity for Processing Information.
''Psychologists don't usually operate to magic, they're usually very precise,'' he said.
As well as the recall experiments, Dr Miller also referred to the seven seas, seven ages of man, seven notes in a musical scale and seven primary colours as evidence there was ''something deep and profound'' behind these numerical events.
While there were plenty of examples of groupings of seven in society, there were equally as many references to four: four ancient elements, four seasons, four Gospels, four suits in a card pack and Olympic Games every four years, said Professor Parker, whose findings were published in the journal Acta Psychiatrica Scandinavica.
While there was still uncertainty about the processes behind the brain's storage capacity limits, the consensus supported the four over seven for the amount of information the brain could absorb, Professor Parker said. ''There may be no limit in storage capacity per se but [there is] a limit to the duration in which items can remain active in short-term memory.''