Monday, 29 October 2012

Selective attention

Today's post starts with a video. This video will take you through an activity. It takes about 90 seconds, and all the instructions and credits are on-screen. Have fun!

I didn't see it the first time I took the test. Now I can't not see it. When I visit kids' classrooms, I show this video every time I have an internet connection. In a class of 30, one or two kids will notice it. Maybe.

This video demonstrates a phenomenon called selective attention. Selective attention happens when we pay so much attention to one thing, that we miss other things going on around us. It's better known as the "cocktail party effect", because it describes how people at a party can focus on a single conversation, even though the room around them is filled with loud music, loads of voices, laughing kids, and who knows what else.

Let's pretend that you have a set of neurons that response to people in white shirts passing basketballs. Maybe you do and maybe you don't, but you definitely have neurons that respond to white, and neurons that respond to moving images, and neurons that respond to people. Let's put all those together to get a group of neurons that respond to people in white shirts passing moving basketballs.

If you're walking by a basketball court and you see someone in white passing a ball, those neurons will fire. (By "fire", I mean, send information in the form of action potentials.) But they won't fire much, because you're not very interested in that - you're more interested in the gorilla doing a jig on the sidelines. But let's say someone asks you to pay attention to the basketball player. "It is very, VERY important that you watch that basketball player," says the mysterious somebody. "The fate of the world depends on it." So you shift your attention to the basketball player. The neurons which respond to white-wearing-basketball-passers suddenly go berserk. They fire loads. And neurons that are firing loads are usually neurons that have something important to say, so you notice, and pay lots of attention to the basketball game.

But heavy firing of some neurons isn't the only thing going on. All your other groups of neurons - those that fire when you see trees, or barking dogs, or gorillas - they aren't firing as much. To the brain, they aren't as important. Your frontal lobe filters them out. It does this though inhibition.

The frontal lobe (in red) is responsible for directing attention, and for inhibiting information that isn't important. (picture from Wikimedia Commons)
Inhibition is a type of electrical activity in the brain. When a neuron is "inhibited", it slows down or stops sending electrical signals. In order to inhibit a neuron, a different neuron has to release inhibitory neurotransmitters. (Neurotransmitters are the chemicals neurons use to talk to each other.) When a neuron receives inhibitory neurotransmitters, it shuts down. The information it has can't go any further. If the brain doesn't want you to pay attention to something, like a gorilla, it inhibits the neurons that "see" and "hear" that gorilla. The information stops. It can't access the higher processing centers - the ones involved in consciousness and awareness. So even if there's a gorilla doing a dance on the basketball court, you don't notice.

The take-home message is this: Our brains are set up to magnify important information and ignore anything that isn't important. What this means is, we don't notice most of what's going on around us. Just think about how much you're missing!


  1. I always feel I miss a lot in different situations like watching a soccer or hockey game. While I'm watching one player or one bit of action I miss something important somewhere else. Thank goodness for instant replay.

    I always thought I missed things because I wasn't paying enough attention.

    It's good to know my brain is just doing what it should be.

    Thanks for an interesting blog.

  2. I have a lot of trouble not listening to all the ambient noise at social gatherings...

  3. It would be great to read more concerning that blog..!Thank you for posting this blog.