Perception Study Explains Why We Overestimate a Problem’s Persistence

What is "prevalence-induced concept change? And how does it affect our perceptions of a problem or a threat? | Science

Law enforcement officials seek out suspicious or criminal behavior just as medical doctors search for cases of disease, and both do so to make their communities and patients healthier. When they succeed at doing so — as crime rates decline and diseases are cured — they should conclude their work is done. According to a new study in the June 29 issue of Science, however, many may fail to recognize the success of their own hard work.

Harvard University's David Levari, the study's lead author, and colleagues investigate the phenomenon of "prevalence-induced concept change," an idea that explains how people can be deceived by their perceptions into thinking that problems persist even when they have, in fact, become much less frequent.

"Our studies suggest that people find it difficult to draw that conclusion simply because their conceptualization of what they are looking for naturally expands as the things they are looking for disappear," said Daniel Gilbert, a professor of psychology at Harvard and co-author of the paper.

The study's results reveal just how susceptible people are to expanding their definitions of a threat or a problem, a phenomenon that could potentially impact a variety of important policy decisions related to issues of health, education, poverty, and violence.

"Wouldn't it be ironic if success tends to erase evidence of itself?" asked Gilbert.

Psychologists have long known that people make judgments in a highly relative context. The things we perceive to be harmful or threatening, for example, depend largely on a person's harmful or threatening experiences. These experiences help define our concepts of what is and what isn't harmful or threatening. However, these concepts are malleable and prone to expansion.

As acts of physical aggression, for example, become less common, people may respond by expanding their concept of physically aggressive behavior, the authors said. For instance, a previously ignored accidental jostle in a crowded room may now be seen as an act of outright aggression. Due to our expanding concept of what physical aggression is, we are likely to conclude its prevalence has remained constant, blinded by our own perception to its actual decline.

Levari and colleagues designed a series of experiments, ranging in complexity, to better understand just how susceptible people are to prevalence-induced concept change.

In one of the experiments, participants in two groups were shown a series of 1,000 dots, which varied in color on a spectrum from purple to blue, and asked to determine whether each dot was blue or not. Eventually, the number of blue dots was decreased for one group and remained unchanged in the other. In the group where blue dots became more scarce, participants began to report purple dots as blue — their concept of a blue dot expanded to include those with a more violet hue.

Additional trials using the dots revealed that the perception deception remained throughout other trials, when the participants were told the number of blue dots would decline, when the decrease happened suddenly and even when participants were offered money to identify and report the decrease.

In similar experiments, the researchers asked participants to rate faces as either "neutral" or "threatening," and to assess the ethics of research proposals. As threatening faces became rarer, participants started to perceive neutral faces as more threatening. When the prevalence of unethical research proposals declined, the participants perceived innocuous proposals as far more questionable.

"Many of the decisions we must make in modern life require that we hold our standards constant and apply them consistently," said Gilbert. However, he said, the results of the study show that people find it difficult to hold their standards constant and that prevalence-induced concept change is remarkably resistant to eradication.

To Gilbert, overcoming the tendency to be duped by ever-shifting perceptions starts with clearly defining a concept to ensure that its definition cannot change or shift in unintended directions.

"If we can say exactly what counts as a suspicious demeanor or a harassing behavior, then we can identify and eliminate those things without worrying that we will inadvertently keep redefining them in the process," Gilbert said.