The human brain is skilled at categorizing. People can quickly recognize a new variation of something they’ve seen before, like a dog, a chair, a jacket, or a lamp. We do this even when we’ve received very little explicit teaching about what distinguishes such categories.
How the brain builds this category knowledge hasn’t been well understood. Drs. Layla Unger and Vladimir Sloutsky from Ohio State University designed a set of experiments to learn how incidental exposure to new things shapes later learning about categories.
The experiments had two phases: an exposure phase and an explicit learning phase. In both phases, participants saw images of imaginary creatures with body parts such as heads, tails, and antennae in various shapes and colors.
In the exposure phase, volunteers played a video game in which a creature appeared in the center, disappeared, and then jumped to the right or left. Participants had to indicate which way the creature jumped, but weren’t told anything about the creatures. Some participants saw creatures made up of random combinations of body parts. Others saw creatures that belonged to different categories, sharing body parts of specific shapes and colors.
For some who saw creatures that belonged to categories, creatures from the same category had many body parts in common. These are called dense categories. For others, the creatures belonged to sparse categories. That is, they had only a few body parts in common, such as having only the same head and tail color. In both cases, creatures in different categories jumped in different directions. This meant that, if participants started to recognize the categories on their own, they could perform the game faster. This let researchers track whether implicit learning had occurred.
After playing this game, participants were told that the creatures belonged to two categories, called “flurps” and “jalets,” and received explicit training on how to tell them apart. The researchers then measured how incidental exposure to the categories affected their explicit learning. Results of the study, which was funded by NIH, were published on May 26, 2022, in Psychological Science.
During the exposure phase, participants who saw flurps and jalets during the game had scores that were similar to those exposed to creatures with random combinations of body parts. This showed that they weren’t recognizing the categories and using them to improve their response times.
However, when it came to explicit learning, prior exposure mattered. Participants exposed to the dense categories learned faster when explicitly taught about them. Exposure to the sparse categories or unrelated creatures didn’t result in faster learning later.
The team repeated the experiments in different ways, making it harder to focus on the categories during the implicit exposure phase. For example, in one they had volunteers focus on a sound during the game instead of a picture.
The researchers found that prior exposure to the dense categories still primed the brain for learning. This study is one of the first to show that people learn from incidental exposure to new things.
“We often observe new things out in the real world without a goal of learning about them,” Sloutsky says. “But we found that simply being exposed to them makes an impression in our mind and leads us to be ready to learn about them later.”
