Speech intelligibility for target and masker with different spectra

The speech intelligibility index (SII) calculation is based on the assumption that the effective range of signal-to-noise ratio (SNR) regarding speech intelligibility is [− 15 dB; +15 dB]. In a specific frequency band, speech intelligibility would remain constant by varying the SNRs above + 15 dB or below − 15 dB. These assumptions were tested in four experiments measuring speech reception thresholds (SRTs) with a speech target and speech-spectrum noise, while attenuating target or noise above or below 1400 Hz, with different levels of attenuation in order to test different SNRs in the two bands. SRT varied linearly with attenuation at low-attenuation levels and an asymptote was reached for high-attenuation levels. However, this asymptote was reached (intelligibility was not influenced by further attenuation) for different attenuation levels across experiments. The − 15-dB SII limit was confirmed for high-pass filtered targets, whereas for low-pass filtered targets, intelligibility was further impaired by decreasing the SNR below − 15 dB (until − 37 dB) in the high-frequency band. For high-pass and low-pass filtered noises, speech intelligibility kept improving when increasing the SNR in the rejected band beyond + 15 dB (up to 43 dB). Before reaching the asymptote, a 10-dB increase of SNR obtained by filtering the noise resulted in a larger decrease of SRT than a corresponding 10-dB decrease of SNR obtained by filtering the target (the slopes SRT/attenuation were different depending on which source was filtered). These results question the use of the SNR range and the importance function adopted by the SII when considering sharply filtered signals

Real-Time Contrast Enhancement to Improve Speech Recognition

An algorithm that operates in real-time to enhance the salient features of speech is described and its efficacy is evaluated. The Contrast Enhancement (CE) algorithm implements dynamic compressive gain and lateral inhibitory sidebands across channels in a modified winner-take-all circuit, which together produce a form of suppression that sharpens the dynamic spectrum. Normal-hearing listeners identified spectrally smeared consonants (VCVs) and vowels (hVds) in quiet and in noise. Consonant and vowel identification, especially in noise, were improved by the processing. The amount of improvement did not depend on the degree of spectral smearing or talker characteristics. For consonants, when results were analyzed according to phonetic feature, the most consistent improvement was for place of articulation. This is encouraging for hearing aid applications because confusions between consonants differing in place are a persistent problem for listeners with sensorineural hearing loss

Age-Related Changes of Myelin Basic Protein in Mouse and Human Auditory Nerve

Age-related hearing loss (presbyacusis) is the most common type of hearing impairment. One of the most consistent pathological changes seen in presbyacusis is the loss of spiral ganglion neurons (SGNs). Defining the cellular and molecular basis of SGN degeneration in the human inner ear is critical to gaining a better understanding of the pathophysiology of presbyacusis. However, information on age-related cellular and molecular alterations in the human spiral ganglion remains scant, owing to the very limited availably of human specimens suitable for high resolution morphological and molecular analysis. This study aimed at defining age-related alterations in the auditory nerve in human temporal bones and determining if immunostaining for myelin basic protein (MBP) can be used as an alternative approach to electron microscopy for evaluating myelin degeneration. For comparative purposes, we evaluated ultrastructural alternations and changes in MBP immunostaining in aging CBA/CaJ mice. We then examined 13 temporal bones from 10 human donors, including 4 adults aged 38–46 years (middle-aged group) and 6 adults aged 63–91 years (older group). Similar to the mouse, intense immunostaining of MBP was present throughout the auditory nerve of the middle-aged human donors. Significant declines in MBP immunoreactivity and losses of MBP+ auditory nerve fibers were observed in the spiral ganglia of both the older human and aged mouse ears. This study demonstrates that immunostaining for MBP in combination with confocal microscopy provides a sensitive, reliable, and efficient method for assessing alterations of myelin sheaths in the auditory nerve. The results also suggest that myelin degeneration may play a critical role in the SGN loss and the subsequent decline of the auditory nerve function in presbyacusis

Cueing listeners to attend to a target talker progressively improves word report as the duration of the cue-target interval lengthens to 2000 ms

Endogenous attention is typically studied by presenting instructive cues in advance of a target stimulus array. For endogenous visual attention, task performance improves as the duration of the cue-target interval increases up to 800 ms. Less is known about how endogenous auditory attention unfolds over time or the mechanisms by which an instructive cue presented in advance of an auditory array improves performance. The current experiment used five cue-target intervals (0, 250, 500, 1000, and 2000 ms) to compare four hypotheses for how preparatory attention develops over time in a multi-talker listening task. Young adults were cued to attend to a target talker who spoke in a mixture of three talkers. Visual cues indicated the target talker’s spatial location or their gender. Participants directed attention to location and gender simultaneously (‘objects’) at all cue-target intervals. Participants were consistently faster and more accurate at reporting words spoken by the target talker when the cue-target interval was 2000 ms than 0 ms. In addition, the latency of correct responses progressively shortened as the duration of the cue-target interval increased from 0 to 2000 ms. These findings suggest that the mechanisms involved in preparatory auditory attention develop gradually over time, taking at least 2000 ms to reach optimal configuration, yet providing cumulative improvements in speech intelligibility as the duration of the cue-target interval increases from 0 to 2000 ms. These results demonstrate an improvement in performance for cue-target intervals longer than those that have been reported previously in the visual or auditory modalities