Hack41.Make Things Invisible Simply by Concentrating (on Something Else)

Hack 41. Make Things Invisible Simply by Concentrating (on Something Else)

What you pay attention to determines what you see, so much so that you can miss things that are immensely obvious to otherslike dancing gorillas, for instance.

Attention acts as a kind of filter, directing all resources to certain tasks and away from others. Nowhere is the impact of attention on what you actually see more evident than in the various experiments on inattention blindness.

Inattention blindness comes up when you're focusing as much attention as you can on a particular task and trying really hard to ignore distractions. It's the name given to the phenomenon of not noticing those distractions, however blatant and bizarre they become. In the most famous experiment on this subject, subjects had to watch a video of a crowd playing basketball. Concentrating on a spurious task, a good number of them were completely blind to the gorilla that walked into view halfway through the game.

3.9.1. In Action

You can watch the basketball video used in the gorilla experiment by Daniel Simons and Christopher Chabris.¹ Find it from the University of Illinois Visual Cognition Lab's page at http://viscog.beckman.uiuc.edu/media/mindhacks.html.²

OK, because you know what's going to happen, this isn't going to work for you, but here's the procedure anyway. Watch the basketball game, and count the number of passes made by the team in white shirts only. Find a friend and set her on the task.

If you were a subject in this experiment for real, counting those passes, what happens next would be completely unexpected: a woman in a gorilla suit walks through the group playing the game and stands in the middle of the screen before walking off again. About half the observers tested in Simons and Chabris's experiment missed the gorilla.

3.9.2. How It Works

Following the passes in the game and counting only some of them is a difficult task. There are two balls and six players, everyone's moving around, and the balls are often obscured. It's all your brain can do to keep up.

Actually, there's a little too much to keep up with. The bottleneck is in visual short-term memory, where the results of visual processing have to be stashed while the actual analysislooking for passes by players in white shirtshappens.

Visual short-term memory , or VSTM, can hold only a small amount of information. Its capacity is limited to the equivalent of about four objects. Now, there are tricks we can use to temporarily increase the size of short-term memory. Repeating a word over and over can lengthen the time it's remembered, for example. When two researchers at Vanderbilt University, J. Jay Todd and René Marois, performed experiments to measure the size of short-term memory,3 they devised their task in such a way that tricks weren't possible. Not only did subjects taking part have to do the memory experimentlooking at a pattern of colored dots and answering a question on it a second laterthey also had to speak numbers out loud for the duration, preventing the word repeating trick from being used. While the full load of the experiment was on VSTM, Todd and Marois looked at their subjects' brain activity using functional magnetic resonance imaging [Hack #4], a technique that produces images in which busy parts of the brain show up brighter.

What they found was a small area on the back surface, in a region called the posterior parietal cortex where the activity increased as the pattern presented in the experiment became more complex. They could see that, as the pattern contained more colored dots, the brain activity grew proportionatelybut only up to four dots. At that point, not only did activity reach its peak, but performance in the short-term memory task did too. This points to a real capacity limit in VSTM.

The capacity is a major factor in counting passes in the basketball game too. There's simply too much going on. That's where attention comes in. Attention is our everyday word for the mechanisms that prioritize processing of some objects, making sure they get into VSTM, and suppress irrelevant information. In this case, when you're watching the gorilla video you have no choice but to pay attention only to fast-moving people dressed in white and concentrate on the ball and whatever it goes behind. That automatically means you're discarding information about slow-moving objects, especially those colored blacklike the gorilla.

So when the dark gorilla suit slowly walks into the game, not only is your attention elsewhere, but also your visual processing system actively throws away information about it, to ensure the short-term memory doesn't get swamped. You don't even perceive the gorilla, despite the ball going behind it so that you're looking through it at some points.

To add a little proof to the pudding: when Simons and Chabris asked viewers to count the passes of the team dressed in black, they became significantly more likely to notice the gorilla, as this time the observation of it wasn't being activity discarded by the brain.

This example shows in a fun way just how powerfully attention affects our perception. It's also an example of the moment-by-moment way we allocate attention, picking some things to focus on and some to ignore, and how this is determined within an overall scheme of the priorities we've set ourselves. Psychologists call this the attentional set, which is the keyword phrase to use if you'd like to find out more.

3.9.3. End Notes

1. Simons, D. J., & Chabris, C. F. (1999). Gorillas in our midst: Sustained inattentional blindness for dynamic events. Perception, 28, 1059-1074. You can get a copy at http://viscog.beckman.uiuc.edu/reprints/index.php.

2. The Visual Cognition Lab (http://viscog.beckman.uiuc.edu/djs_lab) has additional research and demonstrations on inattentional blindness and on related topics.

3. Todd, J. J., & Marois, R. (2004). Capacity limit of visual short-term memory in human posterior parietal cortex. Nature, 428, 751-754.