Time on the Brain: it has Already Happened.

"...The fun thing about neuroscience is that you can do the experiments on yourself. David Eagleman of the Baylor College of Medicine proceeded to treat us as his test subjects. By means of several visual illusions, he demonstrated that we are all living in the past: Our consciousness lags 80 milliseconds behind actual events. “When you think an event occurs it has already happened,” Eagleman said.

In one of these illusions, the flash-lag effect, a light flashes when an object moves past it, but we don’t see the two as coincident; there appears to be a slight offset between them. By varying the parameters of the experiment, Eagleman showed that this occurs because the brain tries to reconstruct events retroactively and occasionally gets it wrong. The reason, he suggested, is that our brains seek to create a cohesive picture of the world from stimuli that arrive at a range of times. If you touch your toe and nose at the same time, you feel them at the same time, even though the signal from your nose reaches your brain first. You hear and see a hand clap at the same time, even though auditory processing is faster than visual processing. Our brains also paper over gaps in information, such as eye blinks. “Your consciousness goes through all the trouble to synchronize things,” Eagleman said. But that means the slowest signal sets the pace.

The cost of hiding the logistical details of perception is that we are always a beat behind. The brain must strike a balance. Cognitive psychologist Alex Holcombe at Sydney has some clever demonstrations showing that certain forms of motion perception take a second or longer to register, and our brains clearly can’t wait that long. Our view of the world takes shape as we watch it.

The 80-millisecond rule plays all sorts of perceptual tricks on us. As long as a hand-clapper is less than 30 meters away, you hear and see the clap happen together. But beyond this distance, the sound arrives more than 80 milliseconds later than the light, and the brain no longer matches sight and sound. What is weird is that the transition is abrupt: by taking a single step away from you, the hand-clapper goes from in sync to out of sync. Similarly, as long as a TV or film soundtrack is synchronized within 80 milliseconds, you won’t notice any lag, but if the delay gets any longer, the two abruptly and maddeningly become disjointed. Events that take place faster than 80 milliseconds fly under the radar of consciousness..."