Carina Pals

Validation of a simple response-time measure of listening effort

This study compares two response-time measures of listening effort that can be combined with a clinical speech test for a more comprehensive evaluation of total listening experience; verbal response times to auditory stimuli (RT(aud)) and response times to a visual task (RTs(vis)) in a dual-task paradigm. The listening task was presented in five masker conditions; no noise, and two types of noise at two fixed intelligibility levels. Both the RTs(aud) and RTs(vis) showed effects of noise. However, only RTs(aud) showed an effect of intelligibility. Because of its simplicity in implementation, RTs(aud) may be a useful effort measure for clinical applications.

Cognitive Compensation of Speech Perception With Hearing Impairment, Cochlear Implants, and Aging: How and to What Degree Can It Be Achieved?

External degradations in incoming speech reduce understanding, and hearing impairment further compounds the problem. While cognitive mechanisms alleviate some of the difficulties, their effectiveness may change with age. In our research, reviewed here, we investigated cognitive compensation with hearing impairment, cochlear implants, and aging, via (a) phonemic restoration as a measure of top-down filling of missing speech, (b) listening effort and response times as a measure of increased cognitive processing, and (c) visual world paradigm and eye gazing as a measure of the use of context and its time course. Our results indicate that between speech degradations and their cognitive compensation, there is a fine balance that seems to vary greatly across individuals. Hearing impairment or inadequate hearing device settings may limit compensation benefits. Cochlear implants seem to allow the effective use of sentential context, but likely at the cost of delayed processing. Linguistic and lexical knowledge, which play an important role in compensation, may be successfully employed in advanced age, as some compensatory mechanisms seem to be preserved. These findings indicate that cognitive compensation in hearing impairment can be highly complicated—not always absent, but also not easily predicted by speech intelligibility tests only.

Effects of Additional Low-pass–filtered Speech on Listening Effort for Noise-band–vocoded Speech in Quiet and in Noise

Objectives: Residual acoustic hearing in electric–acoustic stimulation (EAS) can benefit cochlear implant (CI) users in increased sound quality, speech intelligibility, and improved tolerance to noise. The goal of this study was to investigate whether the low-pass–filtered acoustic speech in simulated EAS can provide the additional benefit of reducing listening effort for the spectrotemporally degraded signal of noise-band–vocoded speech. Design: Listening effort was investigated using a dual-task paradigm as a behavioral measure, and the NASA Task Load indeX as a subjective self-report measure. The primary task of the dual-task paradigm was identification of sentences presented in three experiments at three fixed intelligibility levels: at near-ceiling, 50%, and 79% intelligibility, achieved by manipulating the presence and level of speech-shaped noise in the background. Listening effort for the primary intelligibility task was reflected in the performance on the secondary, visual response time task. Experimental speech processing conditions included monaural or binaural vocoder, with added low-pass–filtered speech (to simulate EAS) or without (to simulate CI). Results: In Experiment 1, in quiet with intelligibility near-ceiling, additional low-pass–filtered speech reduced listening effort compared with binaural vocoder, in line with our expectations, although not compared with monaural vocoder. In Experiments 2 and 3, for speech in noise, added low-pass–filtered speech allowed the desired intelligibility levels to be reached at less favorable speech-to-noise ratios, as expected. It is interesting that this came without the cost of increased listening effort usually associated with poor speech-to-noise ratios; at 50% intelligibility, even a reduction in listening effort on top of the increased tolerance to noise was observed. The NASA Task Load indeX did not capture these differences. Conclusions: The dual-task results provide partial evidence for a potential decrease in listening effort as a result of adding low-frequency acoustic speech to noise-band–vocoded speech. Whether these findings translate to CI users with residual acoustic hearing will need to be addressed in future research because the quality and frequency range of low-frequency acoustic sound available to listeners with hearing loss may differ from our idealized simulations, and additional factors, such as advanced age and varying etiology, may also play a role.