Meyer, of the University of Michigan, worries that the problem goes beyond poor grades. “There’s a definite possibility that we are raising a generation that is learning more shallowly than young people in the past,” he says. “The depth of their processing of information is considerably less, because of all the distractions available to them as they learn.”

Two years ago, Rosen and his colleagues conducted an information-age version of the marshmallow test. College students who participated in the study were asked to watch a 30-minute videotaped lecture, during which some were sent eight text messages while others were sent four or zero text messages. Those who were interrupted more often scored worse on a test of the lecture’s content; more interestingly, those who responded to the experimenters’ texts right away scored significantly worse than those participants who waited to reply until the lecture was over.

David Meyer, a psychology professor at the University of Michigan who’s studied the effects of divided attention on learning, takes a firm line on the brain’s ability to multitask: “Under most conditions, the brain simply cannot do two complex tasks at the same time. It can happen only when the two tasks are both very simple and when they don’t compete with each other for the same mental resources. An example would be folding laundry and listening to the weather report on the radio. That’s fine. But listening to a lecture while texting, or doing homework and being on Facebook—each of these tasks is very demanding, and each of them uses the same area of the brain, the prefrontal cortex.”

The moment of encoding is what matters most for retention, and dozens of laboratory studies have demonstrated that when our attention is divided during encoding, we remember that piece of information less well—or not at all.

Although the students had been told at the outset that they should “study something important, including homework, an upcoming examination or project, or reading a book for a course,” it wasn’t long before their attention drifted: Students’ “on-task behavior” started declining around the two-minute mark as they began responding to arriving texts or checking their Facebook feeds. By the time the 15 minutes were up, they had spent only about 65 percent of the observation period actually doing their schoolwork.

But evidence from psychology, cognitive science, and neuroscience suggests that when students multitask while doing schoolwork, their learning is far spottier and shallower than if the work had their full attention. They understand and remember less, and they have greater difficulty transferring their learning to new contexts.

One large survey found that 80 percent of college students admit to texting during class; 15 percent say they send 11 or more texts in a single class period.

1. Sleep. Using a laptop, cell phone, or iPad late at night can seriously mess with your sleep patterns and habits, potentially leaving you with a sleep disorder. Late night use is also associated with stress and depressive symptoms.

2. Depression. A Swedish study found that participants who felt the need to have their cell phones constantly accessible were more likely to report depressive mental health symptoms. 

3. Addiction. Several studies have actually suggested that the brains of technology abusers develop a certain pattern of change over time. Studies also suggest that the amount of times technology abusers check their gadgets are just enough to trigger the addiction-oriented parts of our brains. 

Frequent users of smartphones quickly get used to the “auto-complete” function of their devices—the way they need only type a few letters and the phone fills in the rest. Maybe too used to it, in fact. This handy function seems to make adolescent users faster, but less accurate, when responding to a battery of cognitive tests, according to research published in 2009 in the journal Bioelectromagnetics.

A study led by researchers at the University of Coventry in Britain surveyed a group of eight- to twelve-year-olds about their texting habits, then asked them to write a sample text in the lab. The scientists found that kids who sent three or more text messages a day had significantly lower scores on literacy tests than children who sent none

The ready availability of search engines is changing the way we use our memories, reported psychologist Betsy Sparrow of Columbia University in a study published in Science last year. When people expect to have future access to information, Sparrow wrote, “they have lower rates of recall of the information itself and enhanced recall instead for where to access it.” It’s good to know where to find the information you need—but decades of cognitive science research shows that skills like critical thinking and problem-solving can be developed only in the context of factual knowledge. In other words, you’ve got to have knowledge stored in your head, not just in your computer.