Basically, the researchers showed the subjects a series of words (half concrete words and half abstract) and non-words and asked them to identify whether or not they were real words as quickly as possible. There were three test groups in the experiment: a group of undergraduates, a group of competitive Scrabble players recruited from a tournament, and a third group of subjects chosen to have the same age distribution as the Scrabble players (with an average age of 57). Additionally, some words were displayed horizontally (like normal words) and others were displayed vertically (like on a Scrabble board).
The researchers found that the undergraduates were the fastest at responding to the word identification tasks (what the journal article terms "lexical decision tasks"), followed by the Scrabble players, and then the age-matched control group. Everyone was slower at identifying abstract words than concrete words, but the Scrabble players had the smallest added delay (120 ms for Scrabble experts versus 270 ms for the control group). The reason that this is interesting is that the added delay for abstract words is believed by some to indicate that people are thinking about the meanings of words when identifying them, and that abstract words take longer to verify due to the extra processing. (A previous study using fMRI scans showed that while certain regions of the brain light up with activity when the subjects are recognizing concrete words, extra regions of the brain come on line when recognizing abstract words.)
The fact that the Scrabble players could recognize abstract words with little additional delay suggests that they are not thinking about word meaning during the word recognition process. This is actually a well-established phenomenon called the concreteness effect.
The two groups of older subjects were far more accurate at identifying words than the undergraduates. Interestingly, Scrabble players and the age-matched group identified horizontal words with quite similar accuracies and speeds, but when the words were arranged vertically, the Scrabble players took a little longer, but had about the same accuracy. The control group took 35-40% longer (though the error bars are big), and made considerably more errors in recognizing words.
The paper then carefully analyzes these results:
The facility with vertical presentation shown by competitive Scrabble players in the present study may be attributable to experience processing words in vertical orientation on the Scrabble board. It is also possible, however, that this facility is due to the extensive word list practice that Scrabble players complete, or to strong word recognition skills that preceded the Scrabble experience. The nature of our design has not allowed us to infer causation.
The subjects were also given a variety of mental tests, and the Scrabble players only did especially well in the Scrabble-related skills (anagramming words and generating words that start with a particular letter). They were able to successfully anagram 3 times more words than the control group and 14 times more words than the undergrads.
The authors conclude the paper well by saying:
The behavior of these visual word recognition experts highlights the experience-driven nature of visual word recognition and pushes the bounds on what we previously considered the endpoint of development of the word recognition system.
So I am inferring from this study that either competitive Scrabble players learn to switch off the parts of the brain that think about the meanings of abstract words or else people who have this skill are preferentially drawn to Scrabble. Either way, someone should rustle up some more Scrabble experts and perform brain scans on them to verify this.