Jennifer B. Tufts

Integration efficiency for speech perception within and across sensory modalities by normal-hearing and hearing-impaired individuals.

In face-to-face speech communication, the listener extracts and integrates information from the acoustic and optic speech signals. Integration occurs within the auditory modality (i.e., across the acoustic frequency spectrum) and across sensory modalities (i.e., across the acoustic and optic signals). The difficulties experienced by some hearing-impaired listeners in understanding speech could be attributed to losses in the extraction of speech information, the integration of speech cues, or both. The present study evaluated the ability of normal-hearing and hearing-impaired listeners to integrate speech information within and across sensory modalities in order to determine the degree to which integration efficiency may be a factor in the performance of hearing-impaired listeners. Auditory-visual nonsense syllables consisting of eighteen medial consonants surrounded by the vowel [a] were processed into four nonoverlapping acoustic filter bands between 300 and 6000 Hz. A variety of one, two, three, and four filter-band combinations were presented for identification in auditory-only and auditory-visual conditions: A visual-only condition was also included. Integration efficiency was evaluated using a model of optimal integration. Results showed that normal-hearing and hearing-impaired listeners integrated information across the auditory and visual sensory modalities with a high degree of efficiency, independent of differences in auditory capabilities. However, across-frequency integration for auditory-only input was less efficient for hearing-impaired listeners. These individuals exhibited particular difficulty extracting information from the highest frequency band (4762-6000 Hz) when speech information was presented concurrently in the next lower-frequency band (1890-2381 Hz). Results suggest that integration of speech information within the auditory modality, but not across auditory and visual modalities, affects speech understanding in hearing-impaired listeners.

Perception of dissonance by people with normal hearing and sensorineural hearing loss.

The purpose of this study was to determine whether the perceived sensory dissonance of pairs of pure tones (PT dyads) or pairs of harmonic complex tones (HC dyads) is altered due to sensorineural hearing loss. Four normal-hearing (NH) and four hearing-impaired (HI) listeners judged the sensory dissonance of PT dyads geometrically centered at 500 and 2000 Hz, and of HC dyads with fundamental frequencies geometrically centered at 500 Hz. The frequency separation of the members of the dyads varied from 0 Hz to just over an octave. In addition, frequency selectivity was assessed at 500 and 2000 Hz for each listener. Maximum dissonance was perceived at frequency separations smaller than the auditory filter bandwidth for both groups of listners, but maximum dissonance for HI listeners occurred at a greater proportion of their bandwidths at 500 Hz than at 2000 Hz. Further, their auditory filter bandwidths at 500 Hz were significantly wider than those of the NH listeners. For both the PT and HC dyads, curves displaying dissonance as a function of frequency separation were more compressed for the HI listeners, possibly reflecting less contrast between their perceptions of consonance and dissonance compared with the NH listeners.

Relationships between the modified rhyme test and objective metrics of speech intelligibility.

Relationships between the modified rhyme test (MRT) and the speech transmission index (STI), and MRT and the speech intelligibility index (SII), have been obtained for additive stationary noise and nonlinear distortion of the speech signal. The former was speech‐spectrum shaped noise, white noise, or −3‐dB/octave noise presented at speech signal‐to‐noise ratios ranging from −25 to +10 dB. The speech distortions were peak clipping or center clipping, with clipping thresholds from 2% to 98% of the cumulative magnitude histogram. Subjects (4 male, 4 female) with normal hearing were seated in an anechoic chamber. Speech was reproduced by a small, high‐fidelity loudspeaker located 2.4 m to the center‐of‐head and the inter‐aural axis. Noise was reproduced by four‐loudspeaker systems and processed to simulate a diffuse field at the ear in the horizontal plane. The revised STI was computed using the standardized test signal [IEC 60268‐16 (2003)] and the speech signal. The SII was calculated using coherence to est...

Perception of roughness by listeners with sensorineural hearing loss

The perception of auditory roughness presumably results from imperfect spectral or temporal resolution. Sensorineural hearing loss, by affecting spectral resolution, may therefore alter roughness perception. In this study, normal-hearing and hearing-impaired listeners estimated the roughness of amplitude-modulated tones varying in carrier frequency, modulation rate, and modulation depth. Their judgments were expected to reflect effects of impaired spectral resolution. Instead, their judgments were similar, in most respects, to those of normally-hearing listeners, except at very slow modulation rates. Results suggest that mild-to-moderate sensorineural hearing loss increases the roughness of slowly fluctuating signals.

The Relationship Between Hearing Acuity and Operational Performance in Dismounted Combat

The ability to detect, identify, and localize sounds is critical for successful execution of military operations. However, very little quantitative data are available to determine the minimum hearing levels needed to execute complex military tasks. In this experiment, wearable hearing loss simulation systems were used to evaluate the effect of audibility on combat effectiveness in a paintball-based simulated military exercise. The results indicate that impaired hearing has a greater impact on the offensive capabilities of dismounted personnel than it does on their survival in combat, likely due to the tendency for individuals with simulated impairment to adopt a more conservative behavioral strategy than those with normal hearing. These preliminary results provide valuable insights into the impact of impaired hearing on combat effectiveness, with implications for the development of improved auditory fitness-for-duty standards, the establishment of performance requirements for acquiring hearing protection technologies, and the refinement of strategies to train military personnel on how to use hearing protection in combat environments.

Attenuation as a function of the canal length of custom-molded earplugs

The fit of a custom-molded earplug (CMEP) and the amount of attenuation it provides can be affected by variables related to the original earmold impression and the subsequent manufacturing process. One variable thought to affect the amount of attenuation is the length of the canal portion of the CMEP. In this pilot study, we systematically examined the relationship between CMEP canal length and attenuation in four human subjects. Two men and two women were fitted with CMEPs extending past the second bend of the ear canal. The attenuation provided by the CMEPs was measured over four visits to the laboratory. Prior to each visit, the canal portion of the subjects test CMEP was shortened by 2mm. As expected, attenuation decreased as canal length decreased for all subjects. However, the rate and pattern of decrease varied markedly. Anecdotal reports of comfort as a function of canal length also varied markedly. Results suggest that the critical region/s in the ear canal for maintaining a good acoustic seal m...

Attenuation as a function of the canal length of custom-molded earplugs: a pilot study.

Custom-molded earplugs (CMEPs) whose canal segments extend beyond the second bend of the ear canal can provide excellent attenuation but can sometimes be uncomfortable. Attenuation was measured for CMEPs whose canal segments were shortened in 2-mm increments. The within-subjects design permitted illustration of the form of the function relating attenuation to canal segment length for individuals. Reduction of attenuation due to canal segment shortening was generally more pronounced for frequencies ≤1000 Hz. Some regions of the canal segments were more critical than others in maintaining attenuation. The relationship between comfort and canal segment length was not straightforward.

Examining the noisy life of the college musician: weeklong noise dosimetry of music and non-music activities

Abstract Objective: To examine the contribution of all daily activities, including non-music activities, to the overall noise exposure of college student musicians, and to compare their “noise lives” with those of non-musician college students. Design: Continuous week-long dosimetry measurements were collected on student musicians and non-musicians. During the measurement period, participants recorded their daily activities in journals. Study sample: 22 musicians and 40 non-musicians, all students (aged 18–24 years) at the University of Connecticut. Results: On every day of the week, musicians experienced significantly higher average exposure levels than did non-musicians. Nearly half (47%) of the musicians’ days exceeded a daily dose of 100%, compared with 10% of the non-musicians’ days. When the exposure due to music activities was removed, musicians still led noisier lives, largely due to participation in noisier social activities. For some musicians, non-music activities contributed a larger share of their total weekly noise exposure than did their music activities. Conclusions: Compared with their non-musician peers, college student musicians are at higher risk for noise-induced hearing loss (NIHL). On a weekly basis, non-music activities may pose a greater risk to some musicians than music activities. Thus, hearing health education for musicians should include information about the contribution of lifestyle factors outside of music to NIHL risk.

Evidence of noise-induced subclinical hearing loss using auditory brainstem responses and objective measures of noise exposure in humans

ABSTRACT Exposure to loud sound places the auditory system at considerable risk, especially when the exposure is routine. The current study examined the impact of routine auditory overexposure in young human adults with clinically‐normal audiometric thresholds by measuring the auditory brainstem response (ABR), an electrophysiological measure of peripheral and central auditory processing. Sound exposure was measured objectively with body‐worn noise dosimeters over a week. Participants were divided into low‐exposure and high‐exposure groups, with the low‐exposure group having an average daily noise exposure dose of ˜11% of the recommended exposure limit compared to the high‐exposure group average of nearly 500%. Compared to the low‐exposure group, the high‐exposure group had delayed ABRs to suprathreshold click stimuli and this prolongation was evident at ABR waves I and III but strongest for V. When peripheral differences were corrected using the I‐V interpeak latency, the high‐exposure group showed greater taxation at faster stimulus presentation rates than the low‐exposure group, suggestive of neural conduction inefficiencies within central auditory structures. Our findings are consistent with the hypothesis that auditory overexposure affects peripheral and central auditory structures even before changes are evident on standard audiometry. We discuss our findings within the context of the larger debate on the mechanisms and manifestations of subclinical hearing loss. HighlightsBody‐worn dosimeters were used to objectively measure sound exposure for one week.Noise‐induced damage is evident in the ABR before it manifests in standard audiometric measures.Routine auditory overexposure affects peripheral and central auditory structures.

The effects of elevated hearing thresholds on performance in a paintball simulation of individual dismounted combat

Abstract Objective: To examine the relationship between hearing acuity and operational performance in simulated dismounted combat. Design: Individuals wearing hearing loss simulation systems competed in a paintball-based exercise where the objective was to be the last player remaining. Four hearing loss profiles were tested in each round (no hearing loss, mild, moderate and severe) and four rounds were played to make up a match. This allowed counterbalancing of simulated hearing loss across participants. Study sample: Forty-three participants across two data collection sites (Fort Detrick, Maryland and the United States Military Academy, New York). All participants self-reported normal hearing except for two who reported mild hearing loss. Results: Impaired hearing had a greater impact on the offensive capabilities of participants than it did on their “survival”, likely due to the tendency for individuals with simulated impairment to adopt a more conservative behavioural strategy than those with normal hearing. Conclusions: These preliminary results provide valuable insights into the impact of impaired hearing on combat effectiveness, with implications for the development of improved auditory fitness-for-duty standards, the establishment of performance requirements for hearing protection technologies, and the refinement of strategies to train military personnel on how to use hearing protection in combat environments.