Comparative illusions are evidence of rational inference in language comprehension

During language comprehension, people sometimes accept sentences that are ungrammatical or semantically implausible and the cognitive mechanism underlying this language illusion is understudied. In this paper, we study the “comparative illusion” (CI) phenomenon where people believe the sentence "More people have been to Russia than I have" to be acceptable while in fact it is semantically ill-formed. We provide a potential explanation for the reasons behind the language illusion from the noisy-channel framework. We hypothesize that comprehenders make rational inference over the perceived sentence by entertaining alternative plausible interpretations and weighing the likelihood of the plausible interpretation being produced with errors. In four experiments, we identified the construction that elicited the most salient illusion effect, established the range of the plausible interpretations, and found that the probability for comprehenders to assign a certain plausible interpretation to the CI sentence is proportional to how likely they think that that interpretation is encapsulated into the CI sentence during speech production. This finding is consistent with the noisy-channel predictions and provides another example supporting the rational behavior underlying language comprehension.