Can pupil dilation reliably measure linguistic salience?

In the field of linguistics, the term salience – how much something stands out – is frequently used to explain a wide range of processes. Examples include the order in which we learn a language and which aspects of a language are most susceptible to change. In these cases, this so-called salience means that some linguistic aspects catch our attention more easily than others.

However, the concept of salience does not have a clear definition, meaning that the term is used in many different ways. In his research, PhD student Vincent Boswijk aimed to determine whether different existing operationalizations of the term could be quantified. His experiment consisted of measuring participants’ pupil dilation while they were listening to spoken sentences. Pupils reflect cognitive processes, for instance when something catches a person’s attention. Pupil dilation also yields insight into the cognitive load that is involved in processing sentences.

The experiment aimed to find a potential common factor in the different definitions of salience. A better understanding of the concept could lead to a better comprehension of language variation and change.

The main finding of the experiment was that half of the data showed that categories that ‘stood out’ resulted in greater pupil dilation than ‘neutral’ categories. This greater pupil dilation points to increased brain activity, likely due to those sentences being more surprising and catching the attention of the participants more often than other sentences. In other words: these sentences were more salient.

Electroencephalography (EEG)
In future research, the experiment will be repeated using electroencephalography (EEG). This method measures brain activity, meaning that cognitive processes can be measured more accurately. Further research will also examine whether the concept of salience can be stripped down even more and will attempt to devise an all-encompassing, workable definition of the concept for the field of linguistics.

Vincent Boswijk is a PhD student in the flagship Culture, Language and Technology. His first article, Salience is in the eye of the beholder: Pupil size reflects acoustically salient variables, has been published with open access on ScienceDirect.