Artwork by Ella Scriven
As Takaun Soho, the zen buddhist, said:
“Preoccupied with a single leaf, you won’t see the tree. Preoccupied with a single tree, you’ll miss the entire forest”.
But what if we wanted to see an interesting leaf?
How would our brain go about filtering out the trees, or even the other leaves? One key way our brain can accomplish this is something called visual gain control. You may ask “Can’t we just focus on everything?”. However, unfortunately, we aren’t quite there yet evolutionarily (at least not until cyborg brain microchips roll out!) Instead we focus with most of our brainpower on one thing at a time, switching quickly to another if required.
So what is visual gain control, and how does it work?
Visual gain control, simply put, is a way for different things to pop out. When we see something, it causes the nerves in our eyes to respond and fire an electrical signal. This signal travels along a pathway of neurons into the brain, eventually reaching a group of neurons associated with what was seen. With visual gain control, as this group of neurons receives the visual information, they process what is in your vision. When most of the group are processing the same thing, that is to say, the area of vision they are responsible for understanding looks the same, they tell each other to fire / send signals less. This happens so that when we see something different, the neurons processing that area are signalling more often than the ones that have seen a largely similar area. This results in the neurons processing that different area out-signalling the others, alerting other parts of your brain to pay more attention to this different area.
A good example of this is when something pops out at you because it has a different colour or texture to the things around it. Consider the example below from a research article on gain control:
Figure 1 here shows a circle, with broadly horizontal lines, except for a small area in the bottom right with a different texture.
Figure 1: An example of an image with two different textures(1)
Figure 2 below is how your neurons may respond to the different areas of figure 1, meaning how much they fire/signal after processing it. Bear in mind, a high response, would lead to more energy, resources, and time spent on focusing on that area. In the top row, we see that without gain control (more specifically “divisive gain control” which is where sensitivity to similar information is reduced(2) ) the entire circle has a high response. Whereas in the bottom row, with gain control, only the small area with a different texture results in a high response, signalling our brain to focus more on this specific “different” area only.
Figure 2, Neurons show selective high response to standout different textures when visual gain control is active (1).
Thanks to visual gain control we are able to focus on areas of vision with noticeable differences, which may be important in helping us with our decision making and learning. Visual gain control enables us to quickly assess and prioritise our attention, helping us respond to our environment. Evolutionarily, this may have helped hunters notice camouflaged animals, or gatherers notice small but bright berries on the forest floor. Visual gain control can also be taken advantage of via bold lettering to help direct readers attention!
Indeed, some form of gain control is present in all of our main senses, helping us filter everything we experience. This allows us to focus on important sounds, feelings, or visual cues without being overwhelmed by everything else. What’s more, gain control is also dysregulated in some mental health related conditions, such as schizophrenia (1) and ADHD(3), and is a promising avenue of research for future treatments to help manage symptoms.
So next time something interesting jumps out at you, be thankful that your brain is able to single it out, helping you to appreciate new/interesting things individually, instead of as part of an overwhelming mess!
References
- Butler PD, Silverstein SM, Dakin SC. Visual perception and its impairment in schizophrenia. Biol Psychiatry. 2008 Jul 1;64(1):40–7.
- Papasavvas CA, Trevelyan AJ, Kaiser M, Wang Y. Divisive gain modulation enables flexible and rapid entrainment in a neocortical microcircuit model. J Neurophysiol. 2020 Mar 1;123(3):1133–43.
- Hauser TU, Fiore VG, Moutoussis M, Dolan RJ. Computational Psychiatry of ADHD: Neural Gain Impairments across Marrian Levels of Analysis. Trends Neurosci. 2016 Feb;39(2):63–73.
