Ever feel like you're trying to remember a thousand different things at once? Well, don't try too hard, since it might be impossible. 

A new study suggests the average person's short-term memory can only hold four items at a time.

Psychologists at the University of Oregon researched short-term memory capacity and a possible underlying link to general intelligence. They found individual short-term memory capacity varied from person to person, but that capacity was a strong indicator of IQ and scholastic aptitude. They also found people with high IQs could think about more things simultaneously.

The study's authors, Professors Edward Awh and Edward Vogel, also pursued a hypothesis that the complexity of memories may have an effect on capacity, but ended up with some surprising results.

While conducting laboratory experiments, they found participants, who ranged in age from 18 to 30, were able to hold four items in active memory regardless of how complex those items were. However, Awh said, the clarity of those items was not perfect, and some people had much clearer memories than others.

They also found a distinct difference between memory capacity and clarity. Awh, the lead author, said 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," he 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."