Benefit of binaural listening as revealed by speech intelligibility and listening effort

Abstract

In contrast to the well-known benefits for speech intelligibility, the advantage afforded by binaural stimulus presentation for reducing listening effort has not been thoroughly examined. This study investigated spatial release of listening effort and its relation to binaural speech intelligibility in listeners with normal hearing. Psychometric functions for speech intelligibility of a frontal target talker masked by a stationary speech-shaped noise were estimated for several different noise azimuths, different degrees of reverberation, and by maintaining only interaural level or time differences. For each of these conditions, listening effort was measured using a categorical scaling procedure. The results revealed that listening effort was significantly reduced when target and masker were spatially separated in anechoic conditions. This effect extended well into the range of signal-to-noise ratios (SNRs) in which speech intelligibility was at ceiling, and disappeared only at the highest SNRs. In reverberant conditions, spatial release from listening effort was observed for high, but not low, direct-to-reverberant ratios. The findings suggest that listening effort assessment can be a useful method for revealing the benefits of spatial separation of sources under realistic listening conditions comprising favorable SNRs and low reverberation, which typically are not apparent by other means. V

Energetic and Informational Components of Speech-on-Speech Masking in Binaural Speech Intelligibility and Perceived Listening Effort

“…Interestingly, this benefit was generally larger when unmasking cues were combined than it was for isolated cues. The increased listening effort benefit for conditions with spatially separated maskers is in agreement with data of Rennies and Kidd (2018), who reported a significant spatial release from listening effort for speech masked by stationary noise. This benefit extended well into the range of high SNRs, at which speech intelligibility was at ceiling.…”

“…The present data allowed us to compare speech intelligibility and listening effort measured in the same subjects for a variety of SOS masking conditions. The functions of speech intelligibility versus listening effort data measured at the same SNRs (Figure 7) showed a similar relation as was observed previously for speech-in-noise conditions (Rennies & Kidd, 2018), that is, most data points were within ±1 ESCU (i.e., one category on the 13-point scale) of a sigmoidal function fitted to the data in the range where both intelligibility and effort were below ceiling. Another similarity to the data of Rennies and Kidd (2018) was the saturated speech intelligibility up to about 5 to 8 ESCU where listening effort varied but intelligibility remained at ceiling.…”

“…For all combinations of cues, this benefit was largest at low SNRs but was reduced or eliminated at high SNRs. The dependence of unmasking benefit on SNR was also observed for spatial unmasking of speech in stationary noise (Rennies & Kidd, 2018) and seems intuitive given that, at a high enough SNR, listening effort will be dominated by SNR and become independent of other unmasking cues. However, the release from listening effort relative to the reference condition extended well into the range of positive SNRs (see Figure 6), and it is important to point out that these effects were unlikely to have been affected by energetic advantages as was observed for the speech intelligibility data.…”

“…Listeners with normal hearing often are able to overcome these adverse effects and may recognize and comprehend the speech of a target voice even at very unfavorable signal-to-noise ratios (SNRs). In a previous study investigating speech in noise perception (Rennies & Kidd, 2018), we found that spatial separation between target and nonspeech noise not only improved speech intelligibility but also reduced listening effort, even in conditions when speech intelligibility was at ceiling, that is, when 100% of the words could be correctly identified. The relationship between improvements in intelligibility and listening effort has important implications for many real-world listening situations, such as those in which the listener uses assistive listening devices (e.g., hearing aids or cochlear implants) to improve spoken communication.…”

“…This ensured that they heard about two entire target sentences before making their choice. The response scale was the same as used in previous studies (Krueger, Schulte, Brand, & Holube, 2017a; Krueger et al., 2017b; Rennies & Kidd, 2018; Rennies, et al, 2014; Schepker et al., 2016) and consisted of 13 listening effort ratings with the seven named categories no effort (1 effort scaling categorical unit, ESCU), very little effort (3 ESCU), little effort (5 ESCU), moderate effort (7 ESCU), considerable effort (9 ESCU), very high effort (11 ESCU), and extreme effort (13 ESCU), as well as six unnamed categories in between. In addition, a 14th category labeled I cannot understand the target talker at all was provided for conditions in which subjects could not hear any target speech (and hence an assessment of listening effort would not be meaningful, see Krueger et al., 2017a).…”