A “granny summary” of the article by Dror Dotan, Ilya Breslavskiy, Haneen Copty-Diab, and Vivian Yousefi
Syntactic priming reveals an explicit syntactic representation of multi-digit verbal numbers
Are multi-digit numbers more than a sequence of number words? To understand this question, let’s take a look at an example from another domain – language. Think about the following two sentences: “Ervin put the car in Dave’s chest” and “Dave put the chest in Ervin’s car”. Both sentences include precisely the same words, yet each sentence has a completely different meaning, because the different word order results in a particular word having different roles in each sentence. For example, in the first sentence, “car” denotes the object being placed, whereas in the second sentence it denotes where an object was placed. The role of each word is determined by the syntactic structure of the sentence, which determines how each word relates to each other word in the sentence. Essentially, the syntactic structure tells us who did what to whom – it’s the “glue” that turns a list of unrelated words into a sentence.
Syntax is not just for grammar classes; our brain can represent the syntactic structures of sentences. Some people have trouble representing such syntactic structures – e.g., because they have an innate learning disorder or because they’ve had a brain injury. This phenomenon is called agrammatism; and while these people can understand words, they will have difficulty in understanding and saying sentences, at least those with complex syntactic structures. To get a feeling of how difficult and frustrating this can be, try figuring out who did what to whom in the sentence “the general who claimed that the policeman who said that the man who heard the boy who shouted played fell retired”.
Back to our topic: numbers have a syntactic structure too. This structure enables us knowing, for example, that ninety-seven is a grammatically valid number whereas seven-ninety is not. Obviously, this reflects the grammatical rules of the number system in English. The interesting question, the one that we examined in the present study, is whether our brain can represent this syntactic structure explicitly, similar to how it can represent the syntactic structure of sentences.
To test this, we used one of the most common research methods in cognitive psychology: priming. This method is based on a simple idea: it’s easier for our brain to do something the second time than it was the first time. For example, if I ask you to say the word “dog” and then say it again, you’ll say it faster the second time. Priming works even if you don’t repeat the same precise word but say a related word. For example, it may take you less time to say “dog” if you’ve just said “bark”, “leash”, or “tail”. This is called semantic priming – the meaning of the second word was similar to the first word. Similarly, there is phonological priming (the sounds of the two words are similar), orthographic priming (the letters of the two words are similar), and so on. The critical point, and the reason for which cognitive researchers use this method, is that if we observed a priming effect – for example, semantic priming (i.e., you said a word faster if the preceding word was semantically related) – this shows that you understood the meaning of the two words, and that your brain represented their meanings. Namely, a priming effect of a particular type is a proof that the brain represents this particular type of information.
In our study, we used a slightly rarer type of priming – syntactic priming: understanding a sentence is easier if you’ve just heard a sentence with the same syntactic structure. Syntactic priming is one kind of evidence indicating that the brain indeed represents syntactic structures. In another variant of syntactic priming, the participants in an experiment are asked to say something; often enough, they will say a sentence having the same syntactic structure as the one they just heard.
Our experiment went as follows: the participant heard a number between 1 and 9,999, and responded by saying a random number in the same range. This hear-and-say procedure was repeated many times. Of course, we didn’t tell them that this was a syntactic priming experiment – we made up some cover story. And sure enough, we found a syntactic priming effect: the syntactic structure of the participants’ responses was similar to the syntactic structure of the number they heard a second earlier. We concluded that their brain understood the syntactic structure of the number, represented it, and stored it in memory for a short period (from the moment they heard the number until they responded).
Our study not only showed that a syntactic representation exists; it also enabled us to start understanding how this syntactic representation works. An interesting finding was that different words in the number had different impact on the syntactic priming effect: the first word in the number had the strongest impact on the priming effect; the second word had a slightly weaker impact; the third word – an even weaker impact; and the fourth word had the weakest impact. This pattern, a decreasing effect of later words, is typical to situations affected by short-term memory (e.g., if I say a list of words and ask you to repeat it in the same order, you’ll remember the first words in the list better than subsequent words). We concluded that our participants represented the syntactic structure using some short-term memory mechanism, and this created the monotonously-decreasing performance pattern.
Why is all this important? From a theoretical point of view, knowing how our brain processes multi-digit numbers, and more generally how it processes various types of syntactic structures, is interesting. For example, because many researchers believe that the ability to process complex syntactic structures is one of the main things that set apart the human brain from the animal brain. But our study is important not only theoretically, but also from an educational point of view. We want to know how our brain represents number syntax because so many children and adults find it extremely difficult to do so, and this may be one of the reasons for which they have difficulties in math. Precisely how many people? Our lab is working on answering this question, but our current estimate is that we’re talking about something like 1 of 7 people. That’s a lot. If we understand better how people without learning disorders process the syntactic structure of numbers, we hope this will help us to characterize the learning disorders that impair this ability, and consequently – to diagnose them and to treat them.
Interested to know more? The full article is here.