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.

5.1 Bottom-up attention and top-down attention, together forever

The signals of bottom-up and top-down attention must be somehow combined to determine where your attention ends up going.

As described in the previous section, top-down attention reflects one’s current goals and task. Bottom-up attention reflects things in a scene that might grab our attention during almost any task, like a unique color. We don’t fully understand how these work together. Sometimes top-down and bottom-up factors compete with each other. This can be seen in the results of an experiment described by Theeuwes (2010).

In the experiment, participants searched for a green diamond presented among a variable number of circles and had to respond to the orientation (horizontal or vertical) of the line segment presented within the diamond shape. So, their task was to find the diamond and pay attention to only it.

In some of the displays, Theeuwes (2010) included a circle that was different in color from all of the rest of the items on the display. The uniqueness of this color tended to attract attention. Because that meant attention was attracted away from the diamond, the results was an elevation in response time for reporting the orientation of the line segment in the diamond.

The graph of the results, shown above, plots the average time to indicate what orientation was in the diamond. The horizontal axis shows that the more stimuli that are presented, the longer it takes people to respond. This is probably because the more objects there were, the longer it took to find the diamond. Also notice that the red line is above the black line. That means that trials with a uniquely-colored distractor slowed response time.

  • By how much, approximately, were responses slowed?

These results illustrate that what we attend to reflects a combination of what is important for our task and extraneous attention-grabbing signals. Objects or signals that grab bottom-up attention are sometimes called salient distractors or exogenous cues. Due to the changing influences of bottom-up and top-down attention, attention may rapidly shift among different stimuli, depending on a combination of task factors and salience of the items.

Some researchers think that top-down and bottom-up attention combine at a “priority map” that emerges from a distributed network involving frontal, partial, temporal areas. Top-down signals largely reflect frontal and parietal areas, while bottom-up attention reflects sensory brain areas. These brain areas’ signals feed into the priority map (possibly within the FEF), which ultimately determines selection.

A schematic, created by Theeuwes and Failing (2020), indicating brain areas that mediate bottom-up attention, top-down attention, and a priority map.

A schematic, created by Theeuwes and Failing (2020), indicating brain areas that mediate bottom-up attention, top-down attention, and a priority map.

5.2 Exercises

Answer these questions and relate them to the learning outcomes ( 2 )

  • What is top-down attention?
  • In the experiment described by Theeuwes (2010), a unique color was used to attract attention. Can you think of something else that might have been used to attract attention?

References

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.