You may have guessed it, but now the science proves it: your cell phone is making you dumber.

Adam Radosavljevic, ThinkStock

A study recently published in Social Psychology discovered that the mere presence of a cell phone on their desk made people perform 20 percent worse on cognitive tasks, compared to those who had their phones stowed away.

Social psychologist Ron Friedman, author of "The Best Place to Work: The Art and Science of Creating an Extraordinary Workplace," said everyone has limited cognitive capacity and how we choose to use our attention is critical, but that choice is often made by the devices in our hands.

"We split our attention just having our cell phone in front of us," Friedman said. "It's because we're monitoring it constantly, even if it's just in our peripheral vision."

Friedman suggested cell phones have an "addictive quality," citing a squirt of dopamine in the brain every time you satisfy your curiosity by checking the phone and finding a new text message or "Words with Friends" alert.

Memory formation may also be negatively affected by cell phone usage. The brain needs rest to transfer information from short-term to long-term memory, but mental breaks are few and far between when every moment is spent checking for something new on the phone.

"We require distraction-free periods to do our best work," Friedman said.

If you want to be more effective in 2015, he said, put the phone out of reach when you need to focus, and turn off any audible alerts that may tempt you to check on your electronic sidekick.

"It's really like dieting. If you are trying to be effective at a diet, you don't want to sit all day at a pastry shop," Friedman said.

Recent research also found cell phones can interfere with the ability to form close relationships. In a lab experiment presented by the University of Essex, the presence of a cell phone caused stark differences in the quality of conversation among two strangers.