Distraction at the office is hardly new, but as screens multiply and managers push frazzled workers to do more with less, companies say the problem is worsening and is affecting business.

While some firms make noises about workers wasting time on the Web, companies are realizing the problem is partly their own fault.

Even though digital technology has led to significant productivity increases, the modern workday seems custom-built to destroy individual focus. Open-plan offices and an emphasis on collaborative work leave workers with little insulation from colleagues’ chatter. A ceaseless tide of meetings and internal emails means that workers increasingly scramble to get their “real work” done on the margins, early in the morning or late in the evening. And the tempting lure of social-networking streams and status updates make it easy for workers to interrupt themselves.

Not all workplace distractions harm productivity. Dr. Mark found that people tended to work faster when they anticipate interruptions, squeezing tasks into shorter intervals of time. Workers’ accuracy suffered little amid frequent interruptions, but their stress rose significantly.

Other studies have found that occasional, undemanding distractions, such as surfing the Web, can help increase creativity and reduce workplace monotony, which may help boost alertness.

Companies are experimenting with strategies to keep workers focused. Some are limiting internal emails—with one company moving to ban them entirely—while others are reducing the number of projects workers can tackle at a time.

The pair instructed workers to let the importance and complexity of their message dictate whether to use cellphones, office phones or email. Truly urgent messages and complex issues merited phone calls or in-person conversations, while email was reserved for messages that could wait.

After an internal study found that workers spent some two hours a day managing their inboxes, the company vowed to phase out internal email entirely.

Workers can still use email with outside customers, but managers have directed workers to communicate with colleagues via an internal social network, which the company began installing earlier this fall, says Robert Shaw, global program director for the “Zero Email” initiative.

Businesses have praised workers for multitasking, “but that isn’t necessarily a good thing,” says Mr. Keene. “When you are focused on just a few things, you tend to solve problems faster. You can’t disguise the problem by looking like you’re really busy.”