Thinking Outside the Grid

What crossword puzzles tell us about how reasoning and memory work

When Dr. Fill, a crossword-solving program, took on the 600 contestants in this year’s American Crossword Puzzle Tournament, its creator predicted it would probably finish among the top 50. Seven expert-level puzzles later, it placed 141st.

The programmer has vowed to bring Dr. Fill back for the 2013 tournament, so it may be premature to say that humans rule the grid. After all, computers have been able to beat world-class chess players and Jeopardy! champions. But Dr. Fill’s less-than-stellar performance—particularly on the quirkier puzzles in the competition—highlights the psychologically complex process behind the enduring pastime of crosswords. Getting from 1 across to 59 down involves a variety of cognitive processes, and for scientists, those processes can reveal intriguing details about memory, recall, language and reasoning and how they work together.

“What’s fascinating is when you think about solving crossword puzzles, you get lots of hints as to how the mind works,” says Raymond Nickerson, G65, a research professor of psychology in the School of Arts and Sciences. Nickerson, an avid crossword puzzle solver, examined the subject in an essay published last year in the journal Psychonomic Bulletin and Review.

“The point of the paper was to illustrate that crosswords do rely on quite a number of cognitive processes,” he says. “I don’t do research on crosswords per se, but it occurred to me that crosswords intersect with a great number of things that I’m interested in, particularly reasoning and memory.”

For example, Nickerson is investigating the concept of conditional reasoning—drawing a conclusion based on an “if…then” proposition (“If it’s Tuesday, this must be Belgium”).

“I believe that in problem solving, we tend to assume that we have found the solution, and once we do, that it’s the only solution to be found,” he says. “Typically, we don’t think further about the problem and discover that there may be other solutions.”

That’s similar to what happens with crossword puzzles: if we’re looking for a noun, we don’t think to look for a verb. And if we find a noun that fits, we don’t explore other possibilities. “That’s somewhat characteristic of the way we solve problems in general,” Nickerson says.

A Four-letter Word Ending in “BT”

As much as science has uncovered about the mind, “there are still a lot of mysteries there,” says Nickerson. “For instance, how does one search memory? That’s not very well known.”

In a crossword puzzle, there are a variety of clues for each word: definitions (some more subtle or tricky than others) or length of the word. Perhaps some of the letters derived from an intersecting clue—known as “orthogonal words,” from a mathematical term meaning to form a right angle. Seasoned solvers also know to look for hints contained within the clues, such as use of question marks or abbreviations. They’re also aware of the unwritten rules most crosswords follow: for example, a clue and its answer are usually expressed in the same part of speech.

And yet, we have no idea how each individual brain goes about the process of combing its database of knowledge to find an answer, Nickerson says. “Say you’re looking for a five-letter word of a particular meaning. You know one or two of the letters. You’re able to search your memory and find the target you’re looking for. How did you do that search?”

The answer, Nickerson says, illustrates the many ways we can search our memories. We can look for words by meaning, by partial length, by observing letters in certain positions, by visual cues, by auditory cues or by some combination of those. For instance: think of a four-letter word ending in “BT.” It isn’t hard for most people to think instantly of the word “DEBT.”

“How is it that __BT gets so quickly to presumably the only four-letter word ending in BT that is in my lexicon?” he asks. “It seems unlikely that a search of my entire lexicon, or anything close to that, is required.” And, he continues, “I am aware of only one common five-letter word ending in BT. I suspect most readers will bring it to mind easily.* It is not at all clear, however, how one goes about retrieving this word.”

And, for that matter, do we even search for words at all? It might be easier to search our memory on the basis of letters, syllables, phonemes (units of sound that distinguish one word from another) or morphemes (meaningful linguistic units of a word).

Sleep on It

Crosswords also raise the tantalizing question, How do we keep track of our mental inventory? With some clues, an answer quickly and unexpectedly bubbles to the surface, surprising even the puzzle solver, Nickerson says. Possibly more intriguing—and certainly frustrating—is the “tip-of-the-tongue” phenomenon that puzzles can evoke. “It is often the case that I am not immediately able to call the target to mind, but I have a strong sense that I will be able to do so with the help of additional clues or, perhaps, just with the passage of time. Author of 'The Ugly Ducking would evoke that feeling for me,” Nickerson writes.

Crossword guru Will Shortz, who edits the puzzles for the New York Times, agrees that sometimes the best strategy for when you’re stumped is to leave the puzzle and come back later. “Perhaps the brain works subconsciously on problems in the interim,” he writes in a piece titled How to Solve the New York Times Crossword Puzzle. “A fresh look at a tough puzzle almost always brings new answers.”

Sometimes the brain will inexplicably continue working on a puzzle even if the solver’s conscious mind does not. Nickerson writes about encountering a puzzle with a six-letter clue, “Former Dolphins quarterback.” Based on intersecting clues, he believed the fourth and sixth letters were both E, but did not immediately know the answer. He left the puzzle unfinished. “Several days later, the name GRIESE came, uninvited, to mind,” he recounts. “I was not thinking about the puzzle at the time and have no recollection of ever consciously trying to think of the name.”

This phenomenon is, of course, not limited to crossword puzzles. “There are a lot of anecdotes in the scientific literature of people working very hard on a problem and not getting very far, and then deciding to just leave it alone, and then coming back to discover they can solve it instantly,” Nickerson says. One example is Dmitri Mendeleyev, who supposedly had the insight for his periodic table of elements in a dream. In psychological terms, this stage of creative problem-solving, in which the mind continues to work on a problem below the level of awareness, is known as “incubation.”

Compulsive Cruciverbalists

Nickerson is quick to point out that while he has been doing crosswords as long as he can remember, he is not compulsive about it—surely not in the league of the characters featured in Wordplay, the 2006 documentary film about devoted puzzlers and cruciverbalists—otherwise known as constructors—or of the hundreds who have been turning out since 1978 for the annual American Crossword Puzzle Tournament.

In fact, Nickerson’s 2011 crossword “think-piece,” as he prefers to call it, was out of academic character. “It was a pretty unorthodox paper. Frankly, I was a little surprised the journal took it. It’s not something I expect to follow up on with my research,” he says.

Both the scientific literature and popular media have looked at the idea that mental gymnastics such as doing crossword puzzles keep the brain agile and can help ward off dementia and Alzheimer’s disease. An observational study by medical researchers of 101 elderly New Yorkers published last year, for example, found that “late life crossword puzzle participation, independent of education, was associated with delayed onset of memory decline in persons who developed dementia.”

“I tend to believe it, because I want to believe that doing crosswords is a way to postpone the ravages of time,” Nickerson says. “In the meantime, whether it works or not, it’s still pleasurable.”

*For those still looking for the five-letter word, it’s DOUBT.

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