An in-depth summary of “Beyond words: Pragmatic inference in behavioral variant frontotemporal degeneration” by Spotorno et al. (2015).

Language is a governing aspect of our everyday interactions; to communicate effectively, we must be able to interpret what other people are saying correctly. This ability to interpret the intention of a speaker becomes essential when meaning is not explicit. Recently, researchers at the Penn FTD Center investigated how patients with the behavioral variant of frontotemporal dementia (bvFTD) may struggle to interpret meaning.

When we listen to someone speak, we infer their meaning based on context. For example, compare the statement “Some of our friends are at the party” to the statement “All of our friends are at the party.” The speaker’s choice of a weaker term like “some” suggests that there is a known reason the speaker chose not to use a stronger term like “all” (e.g. the speaker already knows that their friends Bill and Jack are not at the party).

Researchers at the Penn FTD Center investigated how patients with bvFTD interpreted sentences with the scalar terms “all” and “some.” While distinguishing between “all” and “some” may seem like a simple and automatic interpretation, in actuality, it requires the ability to generate alternative scenarios. Though language skills in bvFTD patients are largely in tact, their social deficits may impair their ability to generate alternative meaning and correctly interpret subtle differences in meaning.

To understand how bvFTD patients might make these inferences, researchers conducted two experiments. In the first experiment, patients were shown one picture. The task was to decide whether or not a given sentence was a good description of the picture. In the second experiment, patients were asked to match a given sentence with one of two pictures. For example, patients were given the sentence “some of the cats are in the box” and given the choice between a picture with some but not all of the cats in the box and a picture with all of the cats in the box. The results from these two experiments show that patients are able to make the correct interpretation when given two alternatives to choose from. However, when patients are only presented with one picture, they will often accept an inappropriate interpretation (for example, accepting that “some of the cats is in the box” is a good description of a picture with all of the cats in the box). How could this be?

Dr. Nicola Spotorno explains,

“In the first scenario, the patients have another picture…specifically, a picture with all of the cats in the box next to another picture with some of the cats in the box. In this situation, the patients have another standard, they have another situation to compare to. In this case, the patient can make a more literal distinction. In the second scenario, however, where they have to agree or disagree with just one picture, they cannot imagine another situation unlike the one that is presented to them. Therefore, even if there is a picture with ‘all of the cats in a box’, they will agree with the statement that ‘some cats are in a box,’ because they cannot imagine other situation where the alternative use of the word ‘some’ would be true. Here, it is difficult for them to make an implied distinction between ‘some’ and ‘all.’”

So, what does this all mean? Taken together, these two complementary experiments suggest that, while bvFTD patients understand the difference in meaning between “some” and “all” statements, they will not make this distinction when left to their own devices. Importantly, this deficit appears to be an inability to generate alternative interpretations, rather than a complete inability to understand complex or subtle language.

This study also explored the brain regions that are necessary to perform this sort of task. If you want to read more about this study, please visit: http://www.ncbi.nlm.nih.gov/pubmed/26150205

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