Effortful listening is experienced by listeners when speech is hard to understand because it is degraded or masked by environmental noise. Pupillometry (i.e., measure of pupil size) can detect effortful listening: pupil size increases when speech is degraded compared to when it is clear. However, the pupil responds to a range of cognitive demands, including linguistic challenges such as syntactic complexity. Here I investigate whether it responds to the need to disambiguate words with more than one meaning, such as ‘bark’ or ‘bank’. Semantic ambiguity is common in English, and previous work indicates that it imposes a processing load. We combine this with an acoustic challenge in a factorial design so the pupil response to these two types of challenge can be directly compared. I found main effects of noise and semantic ambiguity on the pupillary area, indicating that pupil dilation can reflect processes associated with semantic disambiguation as well as noise. Pupil size reflect demands imposed by ambiguity both in the acoustic form of words (i.e. due to degradation) and in word meaning
