Speech masking speech in everyday communication The role of inhibitory control and working memory capacity

Age affects hearing and cognitive abilities. Older people, with and without hearing impairment (HI), exhibit difficulties in hearing speech in noise. Older individuals show greater difficulty in segregating target speech from distracting background noise, especially if the noise is competing speech with meaningful contents, so called informational maskers. Working memory capacity (WMC) has proven to be a crucial factor in comprehending speech in noise, especially for people with hearing loss. In auditory scenes where speech is disrupted by competing speech, high WMC has proven to facilitate the ability to segregate target speech and inhibit responses to irrelevant information. People with low WMC are more prone to be disrupted by competing speech and exhibit more difficulties in hearing target speech in complex listening environments. Furthermore, older individuals with a HI experience more difficulties in switching attention between wanted and irrelevant stimuli, and they employ more resources and time to attend to the stimuli than do normally hearing (NH) younger adults. This thesis investigated the importance of inhibitory control and WMC for speech recognition in noise, and perceived listening effort. Four studies were conducted. In the first study, the aim was to develop a test of inhibitory control for verbal responses, and to investigate the relation between inhibitory control and WMC, and how these two abilities related to speech recognition in noise, in young normally hearing (YNH) individuals. In the second study the aim was to investigate the same relationship as in the first study to further strengthen the validity of the inhibitory test developed, as well as the importance of lexical access. It was also an aim to investigate the influence of age and hearing status on lexical access and WMC, and their respective roles for speech recognition in noise in both YNH and older HI (OHI) individuals. Study one and two showed that, for YNH, inhibitory control was related to speech recognition in noise, indicating that inhibitory control can help to predict speech recognition in noise performance. The relationship between WMC and speech recognition in noise in YNH shifted in the studies, suggesting that this relationship is multifaceted and varying. Lexical access was of little importance for YNH, although for OHI individuals, both WMC and lexical access was of importance for speech