The aim of the present study was to evaluate the influence of age, hearing loss, and cognitive ability on the cognitive processing load during listening to speech presented in noise. Cognitive load was assessed by means of pupillometry (i.e., examination of pupil dilation), supplemented with subjective ratings.
Two groups of subjects participated: 38 middle-aged participants (mean age = 55 yrs) with normal hearing and 36 middle-aged participants (mean age = 61 yrs) with hearing loss. Using three Speech Reception Threshold (SRT) in stationary noise tests, we estimated the speech-to-noise ratios (SNRs) required for the correct repetition of 50%, 71%, or 84% of the sentences (SRT50%, SRT71%, and SRT84%, respectively). We examined the pupil response during listening: the peak amplitude, the peak latency, the mean dilation, and the pupil response duration. For each condition, participants rated the experienced listening effort and estimated their performance level. Participants also performed the Text Reception Threshold (TRT) test, a test of processing speed, and a word vocabulary test. Data were compared with previously published data from young participants with normal hearing.
Hearing loss was related to relatively poor SRTs, and higher speech intelligibility was associated with lower effort and higher performance ratings. For listeners with normal hearing, increasing age was associated with poorer TRTs and slower processing speed but with larger word vocabulary. A multivariate repeated-measures analysis of variance indicated main effects of group and SNR and an interaction effect between these factors on the pupil response. The peak latency was relatively short and the mean dilation was relatively small at low intelligibility levels for the middle-aged groups, whereas the reverse was observed for high intelligibility levels. The decrease in the pupil response as a function of increasing SNR was relatively small for the listeners with hearing loss. Spearman correlation coefficients indicated that the cognitive load was larger in listeners with better TRT performances as reflected by a longer peak latency (normal-hearing participants, SRT50% condition) and a larger peak amplitude and longer response duration (hearing-impaired participants, SRT50% and SRT84% conditions). Also, a larger word vocabulary was related to longer response duration in the SRT84% condition for the participants with normal hearing.
The pupil response systematically increased with decreasing speech intelligibility. Ageing and hearing loss were related to less release from effort when increasing the intelligibility of speech in noise. In difficult listening conditions, these factors may induce cognitive overload relatively early or they may be associated with relatively shallow speech processing. More research is needed to elucidate the underlying mechanisms explaining these results. Better TRTs and larger word vocabulary were related to higher mental processing load across speech intelligibility levels. This indicates that utilizing linguistic ability to improve speech perception is associated with increased listening load.
This study evaluated the relation between age, hearing loss, cognitive abilities, and cognitive processing load during listening. Middle-aged listeners with normal hearing and middle-aged listeners with hearing loss performed speech reception thresholds tests at 50%, 71%, and 84% sentence intelligibility. Cognitive processing load, as measured by the pupil response, systematically increased with decreasing speech intelligibility. Aging and hearing loss were associated with less “release from effort” at increasing speech intelligibility levels. Better linguistic ability was related to higher mental processing load across speech intelligibility levels.
ENT/Audiology and the EMGO+ Institute for Health and Care Research, VU University Medical Center, Amsterdam, The Netherlands.
This work was supported by grants from Stichting Het Heinsius-Houbolt Fonds.
Address for correspondence: Adriana A. Zekveld, ENT/Audiology and the EMGO+ Institute for Health and Care Research, VU University medical center, P.O. Box 7057, 1007 MB Amsterdam, The Netherlands. E-mail: firstname.lastname@example.org.
Received April 16, 2010; accepted October 28, 2010.