NOW It’s something we create for ourselves over and over again, moment by moment."

It’s something we create for ourselves over and over again, moment by moment."

David Eagleman, a neuroscientist at Stanford University, said that we don't experience the world in real time, we're always living a little bit in the past. That's because when we perceive anything, we collect sensory inputs from all over our bodies and the world, and not all of these inputs are processed at the same speed. Sound is processed faster than light. An input from your toes has to travel all the way up your spinal cord, while a signal from your nose doesn't have as far to go.

Wittman explained that there are multiple "nows," comprising different layers of our experience. He outlined three: the functional now, the experienced moment, and mental presence.

The functional now we've touched on already. This is the very small time period in which your brain experiences sensory inputs at the same time. This is mostly unconscious—your brain waiting for the signal from your toe—and takes place in the milliseconds range.

The experienced moment is a more conscious, psychological sense of now, "a slightly longer period in which a single event seems to unfold," as Burdick wrote. This experienced moment has been found repeatedly to be around 2 to 3 seconds. In a paper in PLOS One, researchers looked into this by showing people movie clips—a representation of the kinds of multi-sensory experiences we have in the real world. They scrambled the sequence of events within and beyond intervals of 2 to 3 seconds. They found that within 2 to 3 seconds, the brain was able to fix the order. But above that timescale, there was a dramatic increase in an inability to understand the clips.

Two to 3 seconds for integration might be a “fundamental component of human cognition," the authors wrote, given that similar results have been seen across different tasks. It may "reflect a general organizing principle of human cognition—better defined as the ‘subjective present." Or in other words, “the phenomenal impression of ‘nowness.’”

Wittman said we can also see evidence of this in other places—like a metronome. If you listen to a metronome tick, the ticks are all the same and not being grouped in any particular way. But we do hear a grouping: either one-two, one-two, or if it’s faster, one-two-three, one-two-three. “Although these chunks are not in the metronome,” Wittman said, “our brain creates these units of perception.” For images that can be visually interpreted in different ways, like the duck-rabbit or vase/faces "such changes in perceptual content occur spontaneously, at roughly 3-second intervals," observed one study on the present.

But Wittman said that right now has to be able to do more, so that we can have an integrated whole experience. That's what he calls the third tier: mental presence. It's the right now rooted in the larger, narrative self, and it's built from the other, smaller nows. It's the functional nows and experienced nows linked together, with the help of our memories. This is how everything we see, hear, and feel seems to take place now and yet we also experience the fluid passage of time—our perception is, thankfully, not in static chunks of minute nowness, even as those blocks of right now lie at its core.

In 2007, neurologist Oliver Sacks wrote about a man named Clive Wearing, whose hippocampus, a region of the brain critical for forming new memories, was damaged after he contracted viral encephalitis. Wearing existed only in the “now." If he was holding something in his hand, a chocolate for example—it would constantly present itself as brand new. As his wife described in her memoir, Forever Today:

“Look!” he said. “It’s new!” He couldn’t take his eyes off it.

“It’s the same chocolate,” I said gently.

“No . . . look! It’s changed. It wasn’t like that before . . .” He covered and uncovered the chocolate every couple of seconds, lifting and looking.

“Look! It’s different again! How do they do it?”

The way we experience now is for our survival. We need to understand when things in the outside world happen at the same time, in what order they happened, and be able to use our memories to create a narrative through time