Thinking and using an Internet search engine might seem to be two very different activities. But a study suggests they draw on similar principles.
When you type words into the popular Google search engine, it returns a list of webpages containing those words. The list isn’t ordered any old way: it’s ordered based on how “important” Google deems the pages to be. Google measures a page’s “importance” using a formula based on popularity. It takes into account how many other pages link to that page; how many others, in turn, link to those; and so on.
Now, psychologists have found that our brains return results in much the same way when given a simple task, such as to think of a list of words that start with A.
(Courtesy Google Inc.)
Thomas Griffiths of the University of California, Berkeley, and colleagues ranked the “importance” of over 5,000 words using the same basic Google formula, called PageRank. But instead of Internet links, the researchers tallied mental “links” between words as reflected in answers given in word-association games by people participating in previous studies.
The investigators found that a word’s “PageRank” was a good predictor of how often it would show up when people were asked to think of words that start with A, with B, and so on.
When it came predicting these results, “PageRank” beat two other seemingly reasonable ranking systems: tallies of how often words show up in ordinary writing; and a simple count of direct “links” to a word that doesn’t consider how many words, in turn, link to those linking words.
In the PageRank formula, a page gains “importance” based on how many other pages link to it. But links from pages that are themselves “important,” confer more importance than those that aren’t. Thus, importance can be thought of as flowing through the Web’s link network toward the most highly “linked-in” sites.
One explanation for the new findings, wrote Griffiths and colleagues, could be that connections among brain cells work similarly to Web links. Cells that are targets of many connections might become more active than others, in the same way that highly linked-in websites are deemed more important.
“Our approach indicates how one can obtain novel models of human memory by studying the properties of successful information-retrieval systems, such as Internet search engines,” the group wrote in the study, published in this month’s issue of the research journal Psychological Science. The study also suggests brain science might help design better search engines and data-retrieval systems, they added. “These problems are actively being explored in computer science,” they wrote, but “one might be equally likely to find good solutions by studying the mind.”