Chapter 5 Bottom-up and top-down attention
In the previous chapter we learned that at any one time the sensory signals from only a few objects are being fully processed through the bottleneck(s) and thus are likely to enter memory.
Given the existence of the bottlenecks, we really need ways to prioritise what gets selected for high-level processing. How does your brain decide which objects to attentionally select?
Well, where and when attentional selection happens reflects a combination of factors. In the case of this text, you must have decided to read it. That is, your attentional selection of this text occurred because you gave yourself a task of reading it. While your brain is only able to read one, or at most two, words at a time, your eyes and attention hop along to select and fully process the successive words in this line of text.
We call this kind of selection top-down attention.
Top-down attention is typically voluntary, and thus guided by your expectations and desires, as represented by this inspector intentionally scrutinising individual bits of a crime scene.
Bottom-up attention is quite different - it’s when something in the world grabs your attention. This can sometimes happen even against your will when you are trying to concentrate on something else. The reason for bottom-up attention is a bit like why you have CTRL-C, ESC, or “Force quit” on your computer. After you give your computer a task, sometimes you need to interrupt it. Indeed, every responsive system needs interrupt signals to take them off task when something that might be even more important crops up. That is, no matter how strongly a person is concentrating on a task, there should always be a possibility for unexpected information to trigger attention so that the person remains responsive to unexpected dangers.
If you hear a sudden loud sound, your attention is likely to be taken off, at least momentarily, the task you are performing. This was useful throughout evolutionary history to ensure that our ancestors evaluated sudden movements or sounds that might mark the arrival of another animal such as a predator. Similarly, if someone taps on your shoulder, or another body part, that’s pretty likely to get your attention. We have evolved to be quite vigilant regarding possible threats to our body.
The art of concentration, and studying well, is in part knowledge of what distracts one’s attention, and placing oneself in situations where your attention won’t be distracted.
Unique visual objects in a scene also elicit bottom-up attention. For example, look at the image below - does something in it attract your attention?
The object with the unique color attracts your attention. This is an example of bottom-up attention. When they buy a car, some people deliberately pick an unusual color because they know that when they go shopping, if they forget where they parked their car, they will have little trouble finding it. A pink car will “stick out” conspicuously even in a sea of other cars, if those cars have the more typical colors of black, white, grey, and dark colors.
An object with unique motion direction can also summon attention, as you can see here.
However, not all unique objects in a scene will attract attention. In the below image, the animal whose back you see in the foreground is an elk. Can you find the mountain lion that is stalking it?
Mountain lions and other animals have evolved to have an appearance, and engage in behaviors, that won’t attract the attention of other animals. The next few chapters will be, in part, about what does and doesn’t attract attention.
Theeuwes, Jan. 2010. “Top–down and Bottom–up Control of Visual Selection.” Acta Psychologica 135 (2): 77–99. https://doi.org/10.1016/j.actpsy.2010.02.006.
Theeuwes, Jan, and Michel Failing. 2020. “Attentional Selection: Top-down, Bottom-up and History-Based Biases.” Elements in Perception. https://doi.org/10.1017/9781108891288.