When it comes to the number of pieces of information the mind can cope with before confusion sets in, the "magic" number is seven, psychologists have long said. But did phone companies pick that because of the claim or did folk wisdom say it must be seven because that is what phone companies used?
In 1956, American psychologist George Miller published a paper, "The Magical Number Seven, Plus or Minus Two. Some Limits on Our Capacity for Processing Information", in Psychological Review, arguing the mind could cope with seven chunks of information.
7 plus or minus two felt like pretty good accuracy to psychology and so it became one of the most highly cited psychology articles and has been judged by the Psychological Review as its most influential paper of all time.
But professor of psychiatry Gordon Parker, from the University of NSW in Sydney, Australia, says a re-analysis of the experiments used by Miller shows even a range of 5 to 9 is wrong - Miller missed the correct number by a wide mark.
Writing in Acta Psychiatrica Scandinavica, Scientia, Parker says a closer look at the evidence shows the human mind copes with a maximum of four 'chunks' of information, not seven. "So to remember a seven numeral phone number, say 6458937, we need to break it into four chunks: 64. 58. 93. 7. Basically four is the limit to our perception. That's a big difference for a paper that is one of the most highly referenced psychology articles ever – nearly a 100 percent discrepancy."
Professor Parker says the success of the original paper lies "more in its multilayered title and Miller's evocative use of the word 'magic'," than in the science.
50 years after Miller there is still uncertainty about the nature of the brain's storage capacity limits: "There may be no limit in storage capacity per se but only a limit to the duration in which items can remain active in short-term memory.
"Regardless, the consensus now is that humans can best store only four chunks in short-term memory tasks," he says. Though it's not a good idea to throw that word 'consensus' around just yet.