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Our brain delays visual inputs by 15 seconds to keep us stable

Our brains are constantly bombarded with incoming visual stimuli relating to the world around us. Just like our social media feeds, this stream of new and rich information needs to be kept in check so that we have a sense of continuity in our visual environment. The brain thus acts to “smooth out” small changes in what we perceive so that we get a sense of continuity. And it does this by focusing on what we saw 15 seconds ago.

Researchers at UC Berkeley have discovered that our brains do not update our visual surroundings in real time but rather present us with an image representing an average of what we saw in the past 15 seconds. This has the effect of downplaying the constant changes in light, movement and action that would otherwise add up to a confusing and chaotic visual input. 

“If our brains were always updating in real time, the world would be a jittery place with constant fluctuations in shadow, light and movement, and we’d feel like we were hallucinating all the time,” explained study senior author Professor David Whitney.

“Our brain is like a time machine. It keeps sending us back in time. It’s like we have an app that consolidates our visual input every 15 seconds into one impression so we can handle everyday life,” added study lead author Professor Mauro Manassi.

By merging together recent images and smoothing over subtle changes, our brain tricks us into perceiving a stable environment that is more manageable to process. However, living “in the past” also means that we will not always notice changes in what we see over time. The researchers refer to this phenomenon as “change blindness.”

In their study, published recently in the journal Science Advances, the researchers recruited nearly 100 people to view close-up images of faces which morphed subtly from young to older, or from male to female. The time-lapse videos lasted for just 30 seconds and only included a person’s eyes, brows, nose, mouth, chin, and cheeks – not their head or facial hair – meaning that few clues were given about the age or gender of the person in the image.

After watching the video, participants were asked to assess the age or gender of the image they had seen. The participants consistently picked an image they had viewed halfway through the video instead of the final one, which would have represented the most recent and accurate image.

“One could say our brain is procrastinating,” said Professor Whitney. “It’s too much work to constantly update images, so it sticks to the past because the past is a good predictor of the present. We recycle information from the past because it’s faster, more efficient and less work.”

Indeed, the results suggest the brain operates with a slight lag when processing visual stimuli, and this means that it sacrifices accuracy for a stable picture. This can have both positive and negative implications.

“The delay is great for preventing us from feeling bombarded by visual input in everyday life, but it can also result in life-or-death consequences when surgical precision is needed,” said Professor Manassi. “For example, radiologists screen for tumors and surgeons need to be able to see what is in front of them in real time; if their brains are biased to what they saw less than a minute ago, they might miss something.”

Furthermore, it is important that we understand our perceptions may actually not be an accurate representation of the physical world. Scientists rely on perception for their accuracy when collecting empirical data – the findings of this study indicate that we all have a perceptual bias that may affect our ability to perceive the physical world accurately.

The study provides new insights into what scientists call the mind’s “continuity field,” a function of human perception that involves mechanisms within the brain that continuously bias our visual perception towards our past visual experience. This explains why, for example, we don’t notice when an actor is replaced by a stunt double during the course of a movie. 

Such change blindness reveals how the continuity field is a purposeful function of consciousness and how it helps stabilize the chaotic visual world we live in. 

“We’re not literally blind,” said Professor Whitney. “It’s just that our visual system’s sluggishness to update can make us blind to immediate changes because it grabs on to our first impression and pulls us toward the past. Ultimately, though, the continuity field supports our experience of a stable world.”

By Alison Bosman, Staff Writer

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