Chapter 8 Binding takes time
The previous chapter explained that we can set our attention to process individual locations, or individual features. But we do poorly with combinations of features. The difficulty with encoding combinations of features, but not individual features, can be quite striking in some simple animations, as you will see below.
If the animation above doesn’t work, watch it here.
What’s going on in that animation should be easy to perceive - the color is alternating between green and red, and the left side edge is alternating between leftward-tilted and rightward-tilted. You can also easily see how the features are paired; that is, when the left side is leftward-tilted, the right side is red.
If we speed up the alternation of the two frames, however, we can reveal the difficulty our brain has with combining features (A. O. Holcombe and Cavanagh 2001).
If the above movie doesn’t work on your web browser, watch the same speeded-up version here. It is still easy to see that the individual features are red/green and left/right, but it’s hard to judge which occur at the same time. The brain takes too long to identify combinations of features to know which were presented simultaneously.
The previous chapter explained that we can select objects in the scene by certain individual features such as by location and by color. For example, we can think “red” and our attention will process all the locations containing red more. However, this doesn’t work for combinations of features such as red and leftward-tilted. The present chapter showed another side of our trouble with combinations of features - simply identifying pairs of features can be quite time-consuming.
To experience that more, watch the below two-frame animation. This time, the challenge is to combine two different orientations. At the slow rate (top row), you can do it. But in the middle row, you don’t have enough time. If the below animation doesn’t work in your web browser, try watching it here
Binding can also be time-consuming for color with motion direction, as illustrated by the animation below.
While at the slow rate of the top row, it is easy to judge the pairing of motion direction and white/black color, it is very difficult in the middle row, where the speed is slightly faster.
In each case, the reason for the slow limit on binding, we believe, is that early visual processing stages work very quickly and process the multiple features in parallel. In contrast, determining the pairing of features requires applying limited-capacity resources (there’s a bottleneck!). These processes work more slowly. Possibly, attention must select first one location, and then the other location, to bring the features together before the animation changes. I have set the animations’ playback speed to a rate fast enough that attentional selection is too slow to get this done (Alex O. Holcombe 2009).
In the previous chapter you learned that our brain has a process for attentional selection of an individual feature, but not for combinations of features. In this chapter you learned that combining features can be done, but is time-consuming. In the next chapter, we will put these ideas together to better understand classic findings from visual search experiments that you learned about in first-year psychology.
Answer these questions:
- What do the slow limit on pairing simultaneous features have in common with what was said in the previous chapter about selection?
- How do the demonstrations above relate to Learning Outcome #6 (2)?