How many simple objects can you think about at once? Even though people feel they have rich visual experiences, researchers have found that the average person is only aware of about four items at a time.
This ability, say researchers at the University of Oregon, varies from person to person, and they've found that an individual's capacity of short-term memory is a strong predictor of IQ and scholastic achievement. People with high IQs can think about more things at once.
Because the capacity of the short-term memory system seems to underlie a core aspect of intelligence, cognitive psychologists have been interested in determining what causes a four-item limit for most people. One reasonable idea, which researchers have been tossing about, is that memory capacity might be influenced by the complexity of items being stored.
For example, a four-gigabyte iPhone, the popular new Apple cell phone, might be able to hold about 1,000 four-minute songs, but, of course, far fewer songs would fit in storage if the songs were all 20 minutes in length, explained UO psychology professors Edward Awh and Edward Vogel, co-authors with recent UO graduate Brian Barton on a study published in the July issue of Psychological Science.
Does human memory work the same way? Their study drew some surprising conclusions on the topic. Even when very complex objects had to be remembered by subjects participating in laboratory experiments, participants, who ranged in age from 18 to 30, still were able to hold four items in active memory. However, Awh said, the clarity of those items was not perfect, and some people had much clearer memories than others.
A second finding also surprised the UO team. "While it seems reasonable that people who think about more things at once might also have clearer memories than average, we found that this assumption was not the case," Vogel said.
According to Awh, the lead author on the study, the same people who can remember a lot of objects at one time do not necessarily have clearer memories of those objects. "Knowing the number of things a person can remember tells you nothing about how clear a person's memory may be," Awh said. "So even though people with high IQs can think about more things at once, there are not guarantees about how good those memories might be."
The National Institutes of Health and National Science Foundation supported the research through grants to Awh and Vogel, respectively.