Our Brain Keeps Us 15 Seconds In Past To Help Us See A Stable World

Our eyes are continuously bombarded by an enormous amount of visual information: millions of shapes, colors, and movements constantly changing around us. For the brain, this is no easy task.

For one, the visual world is continually altered due to changes in light, point of view, and other factors. On the other hand, our visual information is constantly changing due to blinking and the fact that our eyes, head, and body are in constant motion.

Credit: 
Karen Nadine

To get a sense of the “noise” of this visual input, hold a phone in front of your eyes and record live video as you walk around and look at different things. The jittery, messy result is exactly what your brain faces at every moment of your viewing experience.

This can also be seen in the following video. The white circle on the right shows possible eye movements, and the blurred spot on the left reveals nervous visual input at each moment.

However, watching never feels like work to us. Instead of perceiving the fluctuations and visual noise that a video might record, we perceive a constantly stable environment. So how does our brain create this illusion of stability? This process has fascinated scientists for centuries and is one of the fundamental questions in the science of vision.

The Brain As A Time Machine

Now, new research led by psychology professors Mauro Manassi of the University of Aberdeen and David Whitney of the University of California at Berkeley has discovered a new mechanism that, among others, may explain this illusory stability.

“The brain automatically smooths out our visual input over time. Instead of analyzing each visual snapshot, we perceive at any given moment an average of what we saw in the last 15 seconds,” explains Manassi. “So by putting objects together to make them appear more similar to each other, our brain tricks us into perceiving a stable environment.”

This living “in the past” may explain why we don’t notice the subtle changes that occur over time.

In other words, the brain is like a time machine that takes us back in time. It’s like an app that consolidates our visual input every 15 seconds into an impression so we can handle everyday life.

“If our brains were always updating in real-time, the world would feel like a chaotic place with constant fluctuations of light, shadow, and movement. We would feel like we were hallucinating all the time,” says Whitney. “We created an illusion to illustrate how this stabilization mechanism works.”

Looking at the video below, the face on the left side ages slowly over 30 seconds, and yet it is very difficult to notice the full extent of the age change. In fact, observers perceive that the face ages are more slowly than it actually does.

To test this illusion, the researchers recruited hundreds of participants and asked them to watch close-ups of faces that morphed chronologically in an age in 30-second timelapse videos.

When asked to state the age of the face at the end of the video, participants almost consistently reported the age of the face that was presented 15 seconds earlier.

“As we watch the video, we are continuously biased towards the past and therefore the brain constantly sends us back to the previous 10 to 15 seconds (where the face was younger). Instead of seeing the latest image in real-time, humans actually see earlier versions because our brain’s update time is about 15 seconds. So this illusion demonstrates that visual smoothing over time can help stabilize perception,” says Manassi.

“What the brain is essentially doing is procrastinating. It’s too much work to constantly deal with every snapshot you get, so the brain sticks to the past because the past is a good predictor of the present,” he adds.

Basically, we recycle information from the past because it’s more efficient, faster, and requires less work.

This idea—which is also supported by other results—of mechanisms within the brain that continually bias our visual perception toward our past visual experience is known as continuity fields.

Our visual system sometimes sacrifices precision for the sake of a seamless visual experience of the world around us. This may explain why, for example, when watching a movie we don’t notice the subtle changes that occur over time, such as the difference between the actors and their doubles.

Repercussions

There are positive and negative implications for our brains to function with this slight delay when processing our visual world. Lag is great for keeping us from feeling bombarded by visual information every day, but it can also have life-or-death consequences when absolute precision is needed.

For example, radiologists review hundreds of images in batches and view several related images one after another. When looking at an X-ray, doctors are typically asked to identify any abnormalities and then classify them. During this visual search and recognition task, researchers found that radiologists’ decisions were based not only on the current image but also on previously viewed images, which could have serious consequences for patients.

The slowness of our visual system to update itself can make us blind to immediate changes because it clings to our first impression and pushes us back into the past. Ultimately, however, continuity fields further our experience of a stable world. At the same time, it’s important to remember that the judgments we make every day are not entirely based on the present, but rather rely heavily on what we’ve seen in the past.

Source: The Conversation


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