Our eyes are continuously bombarded by an enormous amount of visual information – millions of shapes, colours and ever-changing motion all around us. For the brain, this is no easy feat. On the one hand, the visual world alters continuously because of changes in light, viewpoint and other factors. On the other hand, our visual input constantly changes due to blinking and the fact that our eyes, head and body are frequently in motion.
Yet, seeing never feels like work for us. Rather than perceiving the fluctuations and visual noise that a video might record, we perceive a consistently stable environment. So how does our brain create this illusion of stability? This process has fascinated scientists for centuries and it is one of the fundamental questions in vision science. In our latest research, we discovered a new mechanism that, among others, can explain this illusory stability.
Like our social media feeds, our brains are constantly uploading rich, visual stimuli. But instead of seeing the latest image in real time, we perceive in a given moment an average of what we saw in the past 15 seconds. So, by pulling together objects to appear more similar to each other, our brain tricks us into perceiving a stable environment.
We created a visual illusion to illustrate how this stabilisation mechanism works. A face slowly ages for 30 seconds, and yet, it is very difficult to notice the full extent of the change in age. In fact, observers perceive the face as ageing more slowly than it actually is. To test this illusion we recruited hundreds of participants and asked them to view close-ups of faces morphing chronologically in age in 30-second timelapse videos. When asked to tell the age of the face at the very end of the video, the participants almost consistently reported the age of the face that was presented 15 seconds before. As we watch the video, we are continuously biased towards the past and so the brain constantly sends us back to the past (where the face was younger).
In other words, the brain is like a time machine which keeps sending us back in time. If our brains were always updating in real time, the world would feel like a chaotic place with constant fluctuations in light, shadow and movement. We would feel like we were hallucinating all the time.
Our brain's slight delay in processing visual information has its pros and cons. It helps prevent us from feeling overwhelmed by daily visual input, but can be dangerous when precision is needed. For instance, radiologists examine hundreds of images in batches, and their decisions can be influenced by previous images, potentially affecting patient care. This lag can make us miss immediate changes, as we tend to stick with first impressions and past experiences. Our daily judgments are not just based on the present but are heavily influenced by what we have seen before.
Dr Mauro Manassi, School of Psychology
