Whether you're writing a business proposal or playing with your dog, you assume you're focusing on what you're doing. But you're really not as aware as you think you are.

In fact, our attention pulses in and out of focus four times every second. That's according to a team of researchers from Princeton University and the University of California-Berkeley who studied how humans and monkeys pay attention.

"Our subjective experience of the visual world is an illusion," said study co-author Sabine Kastner, a professor of psychology at the Princeton Neuroscience Institute (PNI), in a statement. "Perception is discontinuous, going rhythmically through short time windows when we can perceive more or less."

Their research appears in back-to-back papers in the journal Neuron, with one study focusing on humans and the other on macaque monkeys.

The researchers compared our oscillating attention spans to a spotlight that changes in intensity. Coming on once every 250 milliseconds, this attention spotlight dims as the house lights come up. That's when you stop focusing on the action onstage and your brain notices everything else around you, the scientists say.

"The brain is wired to be somewhat distractible," Ian Fiebelkorn, Ph.D., first author on the macaque paper, told Inverse. "We focus in bursts, and between those bursts we have these periods of distractibility, that's when the brain seems to check in on the rest of the environment outside to see if there's something important going on elsewhere. These rhythms are affecting our behavior all the time."

We don't, of course, notice these jumps in perception. To us, it appears as if we're giving our undivided attention to whatever we're doing. And that's because, the researchers say, our brains fill in the gaps, turning all those disjointed fragments of information into one coherent movie.

Distraction helps us survive

All this makes sense from an evolutionary standpoint. To survive, you need to be aware of what's going on around you, looking out for potential threats.

"It's like if you're going after this shiny red apple in a tree, you want to know if something bigger or with sharper teeth is also going for that apple," Fiebelkorn tells Gizmodo. "Yeah, you're focused on the apple. But not so focused you don't see danger coming."

The teams behind both studies found nearly identical attention patterns in humans and macaques, which might be that the trait has been preserved because it provides such an important evolutionary advantage.

One disadvantage to the study, however, is that only people with epilepsy were included, offering a definite limitation, Gizmodo points out. The researchers counter, however, that because results were so similar between humans and macaques, it's likely that results would also be very much alike between human subjects who do and don't have epilepsy.

The study results may also be useful for studying attention deficit disorders. The researchers speculate that people who get distracted easily or who become hyper focused might be "stuck" in one of the two states of activity — spotlight or house lights — they describe.

Mary Jo DiLonardo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.

You think you're paying attention, but you're not
Our attention pulses in and out of focus four times every second. But researchers say that's OK, because being distracted has actually helped us survive.