Informational masking modulates semantic processing during recognition of syntactically complex speech: evidence from pupillometry.

Introduction: Speech perception in adverse listening environments depends not only on the quality of the acoustic signal but also on listeners' ability to recruit higher-level linguistic information. Although semantic constraints are known to influence recognition of syntactically complex speech, it remains unclear how informational masking, in which competing speech interferes with target-speech processing beyond peripheral acoustic overlap, influences the use of these cues during spoken sentence processing. The present study examined the effects of animacy-based semantic constraints on recognition of subject- and object-relative sentences presented in either an original two-talker speech masker or a time-reversed version of the same masker. Methods: Thirty-seven young adults with normal hearing completed a sentence repetition task while pupil size was recorded continuously. Speech recognition was analyzed using generalized linear mixed-effects models, and pupil responses were analyzed using generalized additive mixed models (GAMMs). Results: Consistent with previous findings, semantic effects were substantially greater for syntactically complex object-relative sentences than for subject-relative sentences. Masker type did not produce a significant overall effect on recognition accuracy, nor did it significantly modify the behavioral semantic effect. In the pupil data, however, semantic condition interacted significantly with masker type: the magnitude and direction of the animacy effect differed between the original- and reversed-speech masker conditions, whereas the corresponding time-varying interaction did not reach significance. Discussion: These findings suggest that informational masking alters how semantic information contributes to processing demands during sentence recognition rather than simply increasing overall listening effort. More broadly, the results demonstrate the value of combining behavioral and pupillometric measures to examine how perceptual and linguistic demands jointly shape spoken language processing.