We have a problem, people: Even though we’re supposed to put the right stuff in the blue bin, a lot of recyclable material nevertheless winds up crammed into landfills. One of the most noteworthy of these is paper: While 64.6 percent of paper and paperboard got recycled in 2012, that still left 24.26 million tons of the stuff discarded, according to the EPA.

Clearly, this is in part because some people still don’t recycle. But our failure to recycle, suggests a new study, is also driven by a cognitive processes that lead us to instinctively miscategorize recyclable objects when they change their shapes or appearances, and thus wrongly throw them out. And that’s a mistake that can be made even by people who are conscientious recyclers in general.

More specifically, the research finds that we’re more likely to recycle flat, pristine paper than balled up or cut up paper. This makes no physical sense, and no environmental sense — but it does make human sense, if you understand the workings of the brain.

The new study, by Remi Trudel, Jennifer Argo, and Matthew Meng of Boston University and the University of Alberta, is in the journal Environment and Behavior. And to understand it, you really need to know one core thing about the human brain: We are hardwired to automatically categorize objects, places, people, things. This is highly important — from knowing who’s your friend and who’s your enemy, to knowing the difference between beds and couches, we need categorization to get around in the world.

Sometimes, though, our categories fail us. We may treat them as more real or “essential” than they actually are — when in fact, they’re often arbitrary constructs. Or, we may put objects into the wrong mental categories based on attributes that mislead us. The latter seems to be the case with our category of “trash” and the attributes that we perceive in crumpled or cut up paper.

Thus in the study, the researchers found that consumers tend to misperceive paper as a non-recyclable object if it has been “distorted” in some way — having lost its basic, pristine shape. Or as the authors put it:

It appears as though the same product (i.e., paper) may have different categorical representations in memory depending on the degree of distortion….Our conceptual explanation is that a piece of paper that has been cut into smaller pieces is more prototypical of garbage or trash and is automatically categorized as trash because of the alterations to its size and form.

The researchers conducted four separate experiments to demonstrate these errant categorization processes at work. In one, 150 college students were divided into three groups — members of one group sat at a computer next to a full sized piece of 8 1/2″ x 11″ paper, members of another sat at a machine next to a crumpled up piece of the same size, and members of a third group sat at a computer next to a smaller 2″ x 4″ piece of paper. The result: those receiving the large and uncrumpled piece of paper said that they were more likely to recycle it, and less likely to put it in the trash, than those in the two other groups said of their own pieces of paper.

Several additional experiments confirmed this result, albeit with a number of variations. Thus, in one study, some participants were given a pair of scissors and a full sized  sheet of paper describing the scissors, while others were given the same but instructed to cut the paper into 8 pieces (to test the scissors’ functioning, supposedly).

Again, participants were more likely to throw out (rather than recycle) the cut paper upon leaving the room. “Once a full sheet of paper is cut into smaller parts, each part exhibits its own individual properties making it more similar to trash and increasing the likelihood that it gets treated as such,” the researchers observed.

And then, there’s how we treat crumpled paper. The experiment on this was really clever: 130 research subjects received a piece of paper with a number printed on it, and were told to memorize the number. Then, some subjects were told to crumple up the paper (so they couldn’t see the number) while others were merely told to turn the paper over (again, so they couldn’t see the number).

A variety of diversionary, “unrelated studies” ensued, and then at their completion, all participants were told to “dispose of all paper on the way out.” A trash bin was near the door, a recycling bin was farther away. The result? Full sheets of paper were recycled 77.4 percent of the time, whereas crumpled paper was only recycled 7.8 percent of the time.

“We consistently show that consumers’ decision to recycle the same product depends on whether the product is intact (i.e., whole) or distorted (i.e., crumpled, cut),” write the authors.

Fortunately, the researchers did find, in their last study, that showing people a sign — depicting the recycling of balled up paper — helped to correct the category errors observed in prior studies. The sign “drastically increased the recycling rates of distorted paper,” they found.

So in short, the research points out two things: That our brains are probably to blame for a lot of paper winding up in landfills, rather than being recycled — and that we need a lot more signage and other forms of communication to correct and dismantle this cognitive error.