Master of Science
Johnsrude, Ingrid S.
Challenges such as background noise may increase “listening effort.” This construct has been operationalized as the recruitment of cognitive resources during listening (objective effort) or as the self-reported feeling of effort (subjective effort). In the current study, I compared these two dimensions of listening effort directly. Normal-hearing adults listened to highly intelligible passages across several signal-to-noise ratios (SNRs), with reaction time on a secondary task (objective effort) and effort ratings (subjective effort) measured in separate blocks. As the SNR became less favourable, subjective effort appeared to increase continuously, while objective effort only began to increase at a much less favourable SNR. This suggests that although listening effort increases with cognitive demand, these two dimensions may respond differently. However, the greater responsiveness of subjective effort may be due to participants rating the difficulty rather than effort. Further, listening effort appeared to increase before speech intelligibility decreased, suggesting that effort helps maintain intelligibility.
Summary for Lay Audience
Have you ever struggled to have a conversation in a noisy environment like a busy café? If so, you likely experienced “listening effort”—the phenomenon of working hard to understand speech. Quite often, people complain of high listening effort even if they can understand speech well, and even if they appear to have normal hearing. Ideally, clinicians would be able to measure listening effort when assessing patients, but no standard method currently exists. This is in part due to the confusion around the definition of listening effort. Some researchers consider it how hard the brain is working to listen (which I call objective listening effort), while others consider it how hard listeners feel like they are working (which I call subjective listening effort). In fact, many argue that these are two distinct dimensions of listening effort. In this study, I compare objective and subjective effort directly. To do this, I had participants with normal hearing listen to many speech passages with noise in the background, which varied from very favourable to unfavourable. In one half of the experiment, I used a cognitive task to measure participants’ objective effort, and in the other half, I used a questionnaire to measure subjective effort. I found that as the intensity of the noise increased, subjective effort (participants’ feeling of effort) increased continuously. In contrast, objective effort (how hard participants’ brains were working) started fairly stable and only began to increase at a much higher noise level. This suggests that both dimensions of listening effort increase as listening difficulty increases, but that they may respond differently. In particular, it appears that subjective effort can be high even when objective effort is not. This was a surprising result, and it may suggest that participants were actually rating how hard the task was rather than the effort they felt. In addition, listening effort appeared to increase before speech understanding dropped, which suggests that people may invest listening effort as a way to keep speech understandable. More knowledge of listening effort may help clinicians to diagnose and treat more cases of hearing loss.
Rovetti, Joseph E., "Listening effort: Separating the subjective from the objective" (2022). Electronic Thesis and Dissertation Repository. 8756.
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