Phonological Mismatch Makes Aided Speech Recognition in Noise Cognitively Taxing Mary Rudner, 1,2 Catharina Foo, 2 Jerker Ro ¨ nnberg, 1,2 and Thomas Lunner 1,3,4 Objectives: The working memory framework for Ease of Language Understanding predicts that speech processing becomes more effortful, thus re- quiring more explicit cognitive resources, when there is mismatch between speech input and pho- nological representations in long-term memory. To test this prediction, we changed the compression release settings in the hearing instruments of expe- rienced users and allowed them to train for 9 weeks with the new settings. After training, aided speech recognition in noise was tested with both the trained settings and orthogonal settings. We postu- lated that training would lead to acclimatization to the trained setting, which in turn would involve establishment of new phonological representations in long-term memory. Further, we postulated that after training, testing with orthogonal settings would give rise to phonological mismatch, associ- ated with more explicit cognitive processing. Design: Thirty-two participants (mean  70.3 years, SD  7.7) with bilateral sensorineural hearing loss (pure-tone average  46.0 dB HL, SD  6.5), bilater- ally fitted for more than 1 year with digital, two- channel, nonlinear signal processing hearing in- struments and chosen from the patient population at the Linko ¨ ping University Hospital were ran- domly assigned to 9 weeks training with new, fast (40 ms) or slow (640 ms), compression release set- tings in both channels. Aided speech recognition in noise performance was tested according to a design with three within-group factors: test occasion (T1, T2), test setting (fast, slow), and type of noise (un- modulated, modulated) and one between-group fac- tor: experience setting (fast, slow) for two types of speech materials—the highly constrained Hager- man sentences and the less-predictable Hearing in Noise Test (HINT). Complex cognitive capacity was measured using the reading span and letter moni- toring tests. Prediction: We predicted that speech recognition in noise at T2 with mismatched experience and test settings would be associated with more explicit cog- nitive processing and thus stronger correlations with complex cognitive measures, as well as poorer perfor- mance if complex cognitive capacity was exceeded. Results: Under mismatch conditions, stronger cor- relations were found between performance on speech recognition with the Hagerman sentences and reading span, along with poorer speech recog- nition for participants with low reading span scores. No consistent mismatch effect was found with HINT. Conclusions: The mismatch prediction generated by the working memory framework for Ease of Lan- guage Understanding is supported for speech rec- ognition in noise with the highly constrained Hag- erman sentences but not the less-predictable HINT. (Ear & Hearing 2007;28;879– 892) The working memory framework for Ease of Lan- guage Understanding (ELU) (Ro ¨nnberg 2003a) pre- dicts that speech understanding requires more mental effort, or cognitive resources, when speech input can- not be easily matched to memory representations. This is referred to as mismatch. We postulate that if the signal processing parameters in the hearing in- strument of an experienced user are changed, a mis- match situation will arise, because the acoustic signal delivered by the hearing instrument will no longer match established memory representations. To test the mismatch hypothesis, we investigated aided speech recognition in noise performance under match and mismatch conditions and its relationship with cognitive processing. Speech Understanding and Explicit Cognitive Processing In an optimum listening situation, the speech signal is processed effortlessly and automatically. This means that the cognitive processing involved is largely unconscious and implicit. However, listening situations are often suboptimum, which means that implicit cognitive processes are insufficient to un- lock the meaning in the speech stream. Resolving ambiguities among previous speech elements and constructing expectations of prospective exchanges in the dialogue are examples of the complex pro- cesses that may arise. These processes are effortful and conscious and thus involve explicit cognitive processing. The listening situation may be suboptimum be- cause cognitive resources are engaged elsewhere, 1 The Swedish Institute for Disability Research, 2 Departments of Behavioural Sciences and Learning, and 3 Technical Audiology, Linko ¨ ping University, Sweden; and 4 Oticon A/S, Research Centre Eriksholm, Snekkersten, Denmark. 0196/0202/07/2806-0879/0 • Ear & Hearing • Copyright © 2007 by Lippincott Williams & Wilkins • Printed in the U.S.A. 879