Impact of background noise and sentence complexity on cognitive processing effort

Speech comprehension in adverse listening conditions requires cognitive pro- cessing demands. Processing demands can increase with acoustically degraded speech but also depend on linguistic aspects of the speech signal, such as syntactic complexity. In the present study, pupil dilations were recorded in 19 normal-hearing participants while processing sentences that were either syntactically simple or complex and presented in either high- or low-level background noise. Furthermore, the participants were asked to rate the sub- jectively perceived difficulty of sentence comprehension. The results showed that increasing noise levels had a greater impact on the perceived difficulty than sentence complexity. In contrast, the processing of complex sentences resulted in greater and more prolonged pupil dilations. The results suggest that while pupil dilations may correlate with cognitive processing demands, acoustic noise has a greater impact on the subjective perception of difficulty.