Establishment of open web platform based on 3D head model for product adaptability analysis and evaluation.

With improved living conditions, the demand for wearable products has increased, particularly for headwear. Traditionally, the dimensions of headwear products are designed according to 1D anthropometric data, such as head length, width, and eye width. However, this design method, applied to fit the 3D human head, results in differences in adaptability, which affect the wearing comfort of the user. Hence, this study aimed to develop an aided design platform based on a three-dimensional standard head shape to evaluate the virtual wearing of headwear products and adaptability testing. Specifically, a WebGL-based service, named the Chinese Headwear Adaptability Testing (CHAT) platform, was established. Validation and user studies were then conducted using an eye massager device. After the product was redesigned according to evaluation by the proposed system, the results show that the comfort and adaptability of the redesigned eye massager were significantly improved. The findings suggest that using the CHAT platform to design headwear products can help achieve a better wearing fit for the products.

Pitch Perception With the Temporal Limits Encoder for Cochlear Implants.

The temporal-limits-encoder (TLE) strategy has been proposed to enhance the representation of temporal fine structure (TFS) in cochlear implants (CIs), which is vital for many aspects of sound perception but is typically discarded by most modern CI strategies. TLE works by computing an envelope modulator that is within the temporal pitch limits of CI electric hearing. This paper examines the TFS information encoded by TLE and evaluates the salience and usefulness of this information in CI users. Two experiments were conducted to compare pitch perception performance of TLE versus the widely-used Advanced Combinational Encoder (ACE) strategy. Experiment 1 investigated whether TLE processing improved pitch discrimination compared to ACE. Experiment 2 parametrically examined the effect of changing the lower frequency limit of the TLE modulator on pitch ranking. In both experiments, F0 difference limens were measured with synthetic harmonic complex tones using an adaptive procedure. Signal analysis of the outputs of TLE and ACE strategies showed that TLE introduces important temporal pitch cues that are not available with ACE. Results showed an improvement in pitch discrimination with TLE when the acoustic input had a lower F0 frequency. No significant effect of lower frequency limit was observed for pitch ranking, though a lower limit did tend to provide better outcomes. These results suggest that the envelope modulation introduced by TLE can improve pitch perception for CI listeners.

Utilizing True Wireless Stereo Earbuds in Automated Pure-Tone Audiometry.

True wireless stereo (TWS) earbuds have become popular and widespread in recent years, and numerous automated pure-tone audiometer applications have been developed for portable devices. However, most of these applications require specifically designed earphones to which the public may not have access. Therefore, the present study investigates the accuracy of automated pure-tone audiometry based on TWS earbuds (Honor FlyPods). The procedure for developing an automated pure-tone audiometer is reported. Calibration of the TWS earbuds was accomplished by electroacoustic measurements and establishing corrected reference equivalent threshold sound pressure levels. The developed audiometer was then compared with a clinical audiometer using 20 hearing-impaired participants. The average signed and absolute deviations between hearing thresholds measured using the two audiometers were 3.1 dB and 6.7 dB, respectively. The overall accuracy rate in determining the presence/absence of hearing loss was 81%. The results show that the proposed procedure for an automated air-conduction audiometer based on TWS earbuds is feasible, and the system gives accurate hearing level estimation using the reported calibration framework.

Speech intelligibility for various head orientations of a listener in an automobile using the speech transmission index.

As well as background noise and the acoustic conditions of the given space, speech intelligibility (SI) is affected by the binaural effect (BE), which is sensitive to the head orientation (HO) of the listener, especially in a small enclosed space such as an automobile. This study uses the speech transmission index (STI) to systematically investigate and predict SI for various HOs of the listener in an automobile. To explore the combined effects of reflections and BE on the auditory perception of speech, several groups of binaural room impulse responses for different speaker locations and HOs are measured in a listening room and an automobile, with the left-side front window (LFW) closed and open, and these are used to calculate the STI. The SI for various configurations is evaluated indirectly using a Chinese STI-SI model. The results show that reflections in the automobile help to increase the STI of the contralateral ear rather than the ipsilateral ear. The LFW is an important reflective boundary but does not always play a dominant role in the STI (SI). Moreover, the STI (SI) can be improved when the listener in the driver seat turns their head inward, i.e., at a negative HO.

A Graphical-User-Interface-Based Azimuth-Collection Method in Autonomous Auditory Localization of Real and Virtual Sound Sources.

Auditory localization of spatial sound sources is an important life skill for human beings. For the practical application-oriented measurement of auditory localization ability, the preference is a compromise among (i) data accuracy, (ii) the maneuverability of collecting directions, and (iii) the cost of hardware and software. The graphical user interface (GUI)-based sound-localization experimental platform proposed here (i) is cheap, (ii) can be operated autonomously by the listener, (iii) can store results online, and (iv) supports real or virtual sound sources. To evaluate the accuracy of this method, by using 12 loudspeakers arranged in equal azimuthal intervals of 30° in the horizontal plane, three groups of azimuthal localization experiments are conducted in the horizontal plane with subjects with normal hearing. In these experiments, the azimuths are reported using (i) an assistant, (ii) a motion tracker, or (iii) the newly designed GUI-based method. All three groups of results show that the localization errors are mostly within 5-12°, which is consistent with previous results from different localization experiments. Finally, the stimulus of virtual sound sources is integrated into the GUI-based experimental platform. The results with the virtual sources suggest that using individualized head-related transfer functions can achieve better performance in spatial sound source localization, which is consistent with previous conclusions and further validates the reliability of this experimental platform.

Binaural speech transmission index with spatialized virtual speaker in near field: Distance and direction dependence.

As well as background noise and reverberation, speaker-to-listener relative location affects the binaural speech transmission index (BSTI) considerably, especially in the near field. To highlight how speaker location influences the BSTI, binaural room impulse responses measured in a low-reverberation listening room are used to obtain the BSTI indirectly and analyze its near-field dependence on distance and direction. The results show that the BSTI based on the better-ear rule is higher when the virtual speaker is located laterally rather than in the anterior or posterior. When the distance-dependent intensity factor is introduced, the distance is the dominant factor, not the azimuth.

A New Approach for Noise Suppression in Cochlear Implants: A Single-Channel Noise Reduction Algorithm.

The cochlea "translates" the in-air vibrational acoustic "language" into the spikes of neural "language" that are then transmitted to the brain for auditory understanding and/or perception. During this intracochlear "translation" process, high resolution in time-frequency-intensity domains guarantees the high quality of the input neural information for the brain, which is vital for our outstanding hearing abilities. However, cochlear implants (CIs) have coarse artificial coding and interfaces, and CI users experience more challenges in common acoustic environments than their normal-hearing (NH) peers. Noise from sound sources that a listener has no interest in may be neglected by NH listeners, but they may distract a CI user. We discuss the CI noise-suppression techniques and introduce noise management for a new implant system. The monaural signal-to-noise ratio estimation-based noise suppression algorithm "eVoice," which is incorporated in the processors of Nurotron® EnduroTM, was evaluated in two speech perception experiments. The results show that speech intelligibility in stationary speech-shaped noise can be significantly improved with eVoice. Similar results have been observed in other CI devices with single-channel noise reduction techniques. Specifically, the mean speech reception threshold decrease in the present study was 2.2 dB. The Nurotron society already has more than 10,000 users, and eVoice is a start for noise management in the new system. Future steps on non-stationary-noise suppression, spatial-source separation, bilateral hearing, microphone configuration, and environment specification are warranted. The existing evidence, including our research, suggests that noise-suppression techniques should be applied in CI systems. The artificial hearing of CI listeners requires more advanced signal processing techniques to reduce brain effort and increase intelligibility in noisy settings.

Time-compression thresholds for Mandarin sentences in normal-hearing and cochlear implant listeners.

Faster speech may facilitate more efficient communication, but if speech is too fast it becomes unintelligible. The maximum speeds at which Mandarin words were intelligible in a sentence context were quantified for normal hearing (NH) and cochlear implant (CI) listeners by measuring time-compression thresholds (TCTs) in an adaptive staircase procedure. In Experiment 1, both original and CI-vocoded time-compressed speech from the MSP (Mandarin speech perception) and MHINT (Mandarin hearing in noise test) corpora was presented to 10 NH subjects over headphones. In Experiment 2, original time-compressed speech was presented to 10 CI subjects and another 10 NH subjects through a loudspeaker in a soundproof room. Sentences were time-compressed without changing their spectral profile, and were presented up to three times within a single trial. At the end of each trial, the number of correctly identified words in the sentence was scored. A 50%-word recognition threshold was tracked in the psychophysical procedure. The observed median TCTs were very similar for MSP and MHINT speech. For NH listeners, median TCTs were around 16.7 syllables/s for normal speech, and 11.8 and 8.6 syllables/s respectively for 8 and 4 channel tone-carrier vocoded speech. For CI listeners, TCTs were only around 6.8 syllables/s. The interquartile range of the TCTs within each cohort was smaller than 3.0 syllables/s. Speech reception thresholds in noise were also measured in Experiment 2, and were found to be strongly correlated with TCTs for CI listeners. In conclusion, the Mandarin sentence TCTs were around 16.7 syllables/s for most NH subjects, but rarely faster than 10.0 syllables/s for CI listeners, which quantitatively illustrated upper limits of fast speech information processing with CIs.

Influence of Audiovisual Training on Horizontal Sound Localization and Its Related ERP Response.

The objective was to investigate the influence of audiovisual training on horizontal sound localization and the underlying neurological mechanisms using a combination of psychoacoustic and electrophysiological (i.e., event-related potential, ERP) measurements on sound localization. Audiovisual stimuli were used in the training group, whilst the control group was trained using auditory stimuli only. Training sessions were undertaken once per day for three consecutive days. Sound localization accuracy was evaluated daily after training, using psychoacoustic tests. ERP responses were measured on the first and last day of tasks. Sound localization was significantly improved in the audiovisual training group when compared to the control group. Moreover, a significantly greater reduction in front-back confusion ratio for both trained and untrained angles was found between pre- and post-test in the audiovisual training group. ERP measurement showed a decrease in N1 amplitude and an increase in P2 amplitude in both groups. However, changes in late components were only found in the audiovisual training group, with an increase in P400 amplitude and decrease in N500 amplitude. These results suggest that the interactive effect of audiovisual localization training is likely to be mediated at a relatively late cognitive processing stage.

Near-field head-related transfer-function measurement and database of human subjects.

Near-field head-related transfer functions (HRTFs) of human subjects are essential to those researching spatial hearing. By using a carefully designed measurement system, near-field HRTFs of human subjects were measured and a database was constructed. The database includes 56 Chinese human subjects, seven source distances from 0.2 to 1.0 m, and 685 directions at each distance for each subject. In the present work, the technique of near-field HRTF measurement is outlined, the performance of the measurement system is assessed and validated, and the resultant database is reported. The database can provide fundamental data for future research.

Auditory Spatial Discrimination and the Mismatch Negativity Response in Hearing-Impaired Individuals.

The aims of the present study were to investigate the ability of hearing-impaired (HI) individuals with different binaural hearing conditions to discriminate spatial auditory-sources at the midline and lateral positions, and to explore the possible central processing mechanisms by measuring the minimal audible angle (MAA) and mismatch negativity (MMN) response. To measure MAA at the left/right 0°, 45° and 90° positions, 12 normal-hearing (NH) participants and 36 patients with sensorineural hearing loss, which included 12 patients with symmetrical hearing loss (SHL) and 24 patients with asymmetrical hearing loss (AHL) [12 with unilateral hearing loss on the left (UHLL) and 12 with unilateral hearing loss on the right (UHLR)] were recruited. In addition, 128-electrode electroencephalography was used to record the MMN response in a separate group of 60 patients (20 UHLL, 20 UHLR and 20 SHL patients) and 20 NH participants. The results showed MAA thresholds of the NH participants to be significantly lower than the HI participants. Also, a significantly smaller MAA threshold was obtained at the midline position than at the lateral position in both NH and SHL groups. However, in the AHL group, MAA threshold for the 90° position on the affected side was significantly smaller than the MMA thresholds obtained at other positions. Significantly reduced amplitudes and prolonged latencies of the MMN were found in the HI groups compared to the NH group. In addition, contralateral activation was found in the UHL group for sounds emanating from the 90° position on the affected side and in the NH group. These findings suggest that the abilities of spatial discrimination at the midline and lateral positions vary significantly in different hearing conditions. A reduced MMN amplitude and prolonged latency together with bilaterally symmetrical cortical activations over the auditory hemispheres indicate possible cortical compensatory changes associated with poor behavioral spatial discrimination in individuals with HI.