Activity (Alternative) 7.6 The Attentional Bottleneck

The experiment demonstrated in this activity provides yet more proof that attention is a far scarcer commodity than we might think.

Activity Description
The user clicks the white square at left to start a trial. Half a second later, the square fills up with 20 red and green circles. Then, between 500–1000 ms later, one of the circles becomes brighter. At the same time, the color of the brightened disk may change, from red to green or from green to red. The user’s job at this point is to try to decide what color the probed disk was before it got brighter. Half the time the color will have changed, and half the time it will be the same. For example, a dark red disk might be replaced by a bright red disk or a bright green disk. In either case, the user clicks the button below the display to indicate that the disk was originally red.

After doing the activity many times, it becomes apparent that it is very difficult to accurately guess what color the dot was before it became brighter. Performance is usually close to 50% correct, which is chance level.

What's Going On Here?
Your visual system is great at detecting everything in front of your face—for example, you can see all 20 of the circles at the start of each trial in this experiment just fine. Likewise, your memory is (despite what you might think the day after taking your final exams) pretty darn good.

But getting a stimulus from the visual processes to the memory processes requires attention, and this is where the problem lies. It’s not that your attentional processes are faulty—when you do pay attention to a visual stimulus, you’re quite good at putting all aspects of the stimulus together to form a coherent, memorable whole. (Imagine, for example, that you saw just one circle instead of 20. In that case, you would be able to accurately report the color of the circle nearly every time.) Rather, as this and many other experiments show, attentional resources are limited.

This fact leads to the notion of an attentional bottleneck. If you happen to be looking at the circle that changes brightness at the exact time the change occurs, the circle will be likely to make it through the bottleneck into memory, and you will be able to say what color it was before the change. Otherwise, all you will remember is a bunch of green and red circles, and you will probably be deciding by chance what color the cued circle was before the change occurred.