How We Make Quick Decisions About the Number of Objects We See

Source: Generated with AI on September 9, 2024

You often have to make quick judgments about the number of objects you encounter in the world. You might see a group of people walking toward you. It is useful to know whether there are roughly five, 10, or 20. You see some toys on the floor, it is helpful to judge the approximate number that are there.

When there are more than about five objects, you won’t get an exact count, you’re generally pretty good at making rough estimates. As a result, psychologists have studied the factors that drive this sense of perceived numerosity (that is the number of things you’re seeing).

The number of distinct objects that are visible clearly plays a role, though our judgments are really approximate. In addition, the less chaotic the set of objects, the more of them there appear to be.

A 2024 paper by Chuyan Qu, Michael Bonner, Nicholas DeWind, and Elizabeth Brannon published in the Journal of Experimental Psychology: General examined this phenomenon in more detail. They were focused on two questions. First, if the objects in a group feel like they belong together, does that affect your judgments of how many there are? If so, what aspect of your ability to see affects that judgment?

They showed people pairs of groups of objects, where each group had between eight and 16 objects. They would flash the pair for 750 milliseconds (three-quarters of a second) and then ask whether the group on the left or the right had more objects in it. If the difference in number is large (say, eight on the left and 16 on the right), then this task is easy. If the difference is small (say 11 on the left and 13 on the right), then this task is hard.

In the first study, they varied whether the objects in the group tended to be found together in real life. A group of flowers, plants, and small animals tend to be found together. That is, these groups are coherent. A group of flowers, medical equipment, and trucks does not tend to be found together. These groups are not coherent. In this study, groups were constructed that different in how coherent the group of objects was.

The researchers were interested in whether more coherent groups are seen as larger than less coherent groups. If so, then when people are faced with two groups that have a similar number of objects, but the groups differ in coherence, they should often select the group that is more coherent as the larger group. In fact, that is what they found. People generally recognized which group was larger, but when they were close (or equal) in number, there was a bias to select the group that was more coherent.

How do people do that?

One possibility is that people identify the objects and use the conceptual relationships between them to figure out the degree of coherence. However, people are making these judgments quickly. Remember, they see the pair of groups for under a second.

So, perhaps they are responding based on simpler visual features of the objects. In a second study, they compared pictures of the objects to blurred objects that were harder to identify to see whether the coherence effect was still obtained. In a third study, they looked to see whether they could still get this coherence effect when the objects were completely scrambled so that you had information about color and some of the component shapes, but could not identify the object at all.

Surprisingly, in both cases, the coherence effect was still obtained. That is, the more coherent set of objects was still seen as more numerous, even when the objects themselves could not be identified.

How is that possible?

In natural scenes, coherent sets of objects often have similar kinds of low-level visual properties. The kinds of plants, leaves, and small animals that appear in a forest scene have a similar set of colors and organic shapes. Those visual features differ from what you would see in a city scene or in a hospital. Over years of being in different kinds of situations, your visual system has actually learned what kinds of simple visual properties tend to go together. These properties then alert you to the kind of situation you’re in.

Why would an array of objects that is coherent seem larger than an array that is not? How in general might you make judgments about the relative size of groups that you see quickly? In real-world scenes, you have to pick out a group from among a number of other objects that are not part of that group. For example, you might see a group of people walking dogs in a park. You want to count the people and dogs, but not the trees, fountains, and benches. So, having similar kinds of organic forms pop out as part of a group would be helpful. Similarly, if there were lots of coins on your desk, you would want to separate them quickly from pens, desk toys, or books.

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So, isolating things with similar properties helps us to make judgments all the time. We group things that we think are probably going to go together. Doing this just on the basis of simple visual features will lead us to make some mistakes that we may have to correct later by using slower mental processes like identifying each object and counting. But, most of the time, we’ll make pretty reasonable judgments quickly, which will enable us to act efficiently.