Eyes on the Pupil Size: Pupillary Response During Sentence Processing in Aphasia

Individuals with chronic agrammatic aphasia demonstrate real-time sentence processing difficulties at the lexical and structural levels. Research using time-sensitive measures, such as priming and eye-tracking, have associated these difficulties with temporal delays in accessing semantic representations that are needed in real time during sentence structure building. In this study, we examined the real-time processing effort linked to sentence processing in individuals with aphasia and neurotypical, age-matched control participants as measured through pupil reactivity (i.e., pupillometry). Specifically, we investigated whether a semantically biased lexical cue (i.e., adjective) influences the processing effort while listening to complex noncanonical sentences.

In this eye-tracking while listening study (within-subjects design), participants listened to sentences that either contained biased or unbiased adjectives (e.g., venomous snake vs. voracious snake) while viewing four images, three related to nouns in the sentence and one unrelated, but a plausible match for the unbiased adjective. Pupillary responses were collected every 17 ms throughout the entire sentence.

While age-matched controls demonstrated increased pupil response throughout the course of the sentence, individuals with aphasia showed a plateau in pupil response early on in the sentence. Nevertheless, both controls and individuals with aphasia demonstrated reduced processing effort in the biased adjective condition.

Individuals with aphasia are sensitive to lexical-semantic cues despite impairments in real-time lexical activation during sentence processing.