The detection of 'virtual' objects using echoes by humans: Spectral cues.

Some blind people use echoes to detect discrete, silent objects to support their spatial orientation/navigation, independence, safety and wellbeing. The acoustical features that people use for this are not well understood. Listening to changes in spectral shape due to the presence of an object could be important for object detection and avoidance, especially at short range, although it is currently not known whether it is possible with echolocation-related sounds. Bands of noise were convolved with recordings of binaural impulse responses of objects in an anechoic chamber to create 'virtual objects', which were analysed and played to sighted and blind listeners inexperienced in echolocation. The sounds were also manipulated to remove cues unrelated to spectral shape. Most listeners could accurately detect hard flat objects using changes in spectral shape. The useful spectral changes for object detection occurred above approximately 3 kHz, as with object localisation. However, energy in the sounds below 3 kHz was required to exploit changes in spectral shape for object detection, whereas energy below 3 kHz impaired object localisation. Further recordings showed that the spectral changes were diminished by room reverberation. While good high-frequency hearing is generally important for echolocation, the optimal echo-generating stimulus will probably depend on the task.

Development and evaluation of the British English coordinate response measure speech-in-noise test as an occupational hearing assessment tool.

OBJECTIVE: The studies described in this article outline the design and development of a British English version of the coordinate response measure (CRM) speech-in-noise (SiN) test. Our interest in the CRM is as a SiN test with high face validity for occupational auditory fitness for duty (AFFD) assessment. DESIGN: Study 1 used the method of constant stimuli to measure and adjust the psychometric functions of each target word, producing a speech corpus with equal intelligibility. After ensuring all the target words had similar intelligibility, for Studies 2 and 3, the CRM was presented in an adaptive procedure in stationary speech-spectrum noise to measure speech reception thresholds and evaluate the test-retest reliability of the CRM SiN test. STUDY SAMPLE: Studies 1 (n = 20) and 2 (n = 30) were completed by normal-hearing civilians. Study 3 (n = 22) was completed by hearing impaired military personnel. RESULTS: The results display good test-retest reliability (95% confidence interval (CI) < 2.1 dB) and concurrent validity when compared to the triple-digit test (r ≤ 0.65), and the CRM is sensitive to hearing impairment. CONCLUSION: The British English CRM using stationary speech-spectrum noise is a "ready to use" SiN test, suitable for investigation as an AFFD assessment tool for military personnel.

Use of binaural and monaural cues to identify the lateral position of a virtual object using echoes.

Under certain conditions, sighted and blind humans can use echoes to discern characteristics of otherwise silent objects. Previous research concluded that robust horizontal-plane object localisation ability, without using head movement, depends on information above 2 kHz. While a strong interaural level difference (ILD) cue is available, it was not clear if listeners were using that or the monaural level cue that necessarily accompanies ILD. In this experiment, 13 sighted and normal-hearing listeners were asked to identify the right-vs.-left position of an object in virtual auditory space. Sounds were manipulated to remove binaural cues (binaural vs. diotic presentation) and prevent the use of monaural level cues (using level roving). With low- (<2 kHz) and high- (>2 kHz) frequency bands of noise, performance with binaural presentation and level rove exceeded that expected from use of monaural level cues and that with diotic presentation. It is argued that a high-frequency binaural cue (most likely ILD), and not a monaural level cue, is crucial for robust object localisation without head movement.

Simulating the effect of interaural mismatch in the insertion depth of bilateral cochlear implants on speech perception.

A bilateral advantage for diotically presented stimuli has been observed for cochlear implant (CI) users and is suggested to be dependent on symmetrical implant performance. Studies using CI simulations have not shown a true "bilateral" advantage, but a "better ear" effect and have demonstrated that performance decreases with increasing basalward shift in insertion depth. This study aimed to determine whether there is a bilateral advantage for CI simulations with interaurally matched insertions and the extent to which performance is affected by interaural insertion depth mismatch. Speech perception in noise and self-reported ease of listening were measured using matched bilateral, mismatched bilateral and unilateral CI simulations over four insertion depths for seventeen normal hearing listeners. Speech scores and ease of listening reduced with increasing basalward shift in (interaurally matched) insertion depth. A bilateral advantage for speech perception was only observed when the insertion depths were interaurally matched and deep. No advantage was observed for small to moderate interaural insertion-depth mismatches, consistent with a better ear effect. Finally, both measures were poorer than expected for a better ear effect for large mismatches, suggesting that misalignment of the electrode arrays may prevent a bilateral advantage and detrimentally affect perception of diotically presented speech.

Identification of the lateral position of a virtual object based on echoes by humans.

Echolocation offers a promising approach to improve the quality of life of people with blindness although little is known about the factors influencing object localisation using a 'searching' strategy. In this paper, we describe a series of experiments using sighted and blind human listeners and a 'virtual auditory space' technique to investigate the effects of the distance and orientation of a reflective object and the effect of stimulus bandwidth on ability to identify the right-versus-left position of the object, with bands of noise and durations from 10-400 ms. We found that performance reduced with increasing object distance. This was more rapid for object orientations where mirror-like reflection paths do not exist to both ears (i.e., most possible orientations); performance with these orientations was indistinguishable from chance at 1.8 m for even the best performing listeners in other conditions. Above-chance performance extended to larger distances when the echo was artificially presented in isolation, as might be achieved in practice by an assistive device. We also found that performance was primarily based on information above 2 kHz. Further research should extend these investigations to include other factors that are relevant to real-life echolocation.

Early detection of non-organic hearing loss using a simple tone-in-noise test.

Early detection of non-organic hearing loss (NOHL) is important in order to ensure appropriate management decisions. One possible audiometric test for achieving this is the tone-in-noise (TIN) test although its current format is not widely applicable and may not optimize accuracy. We sought to investigate a modified TIN test, using narrowband noise, and the influence of different noise levels and alternative approaches to determining the outcome. Seventy-five normal-hearing and 8 hearing-impaired subjects were asked to feign or exaggerate a hearing loss. The shift in genuine or exaggerated/feigned thresholds with the introduction of ipsilateral noise was determined. The TIN test was able to accurately separate between genuine and feigned thresholds when using narrowband noise presented at the effective masking level corresponding to the apparent tone threshold and using a 'fail' criterion of a repeatable threshold shift of ≥ 10 dB at one or more frequencies. It also produced similar shifts in exaggerated thresholds. In conclusion, this modified TIN test is a potentially accurate method to rapidly identify unilateral and bilateral NOHL in a wide range on contexts and could be applied to automated audiometry.

Lateralization of high-frequency pure tones with interaural phase difference and bone conduction.

This study tested the prediction that interaural phase differences (IPDs) are converted to interaural level differences (ILDs) with bilateral bone-conduction stimulation due to the effects of acoustic interference arising from transcranial transmission. Seven normal-hearing listeners judged the lateral position of 3000-6000-Hz pure tones, presented via bone vibrators on the mastoids, as a function of IPD. Evidence for lateralization was obtained in five listeners despite humans being insensitive to IPD in pure tones at these frequencies. The direction of lateralization depended on frequency, as well as IPD, for three listeners. It is argued that these findings are consistent with the conversion of external IPD to internal ILD during transcranial transmission. Inter-individual variation in lateralization was apparent and no evidence of lateralization was found in two listeners at the frequency tested, which may reflect, at least in part, inter-individual variation in transcranial transmission properties. The notion that external IPD within the waveform fine-structure at high-frequencies does not influence localization with air conduction may not apply to bone conduction due to the acoustic interference effects.

Learning to discriminate interaural time differences: an exploratory study with amplitude-modulated stimuli.

The advent of bilateral cochlear implants (CIs) has increased interest in learning on binaural tasks, and studies in normal-hearing listeners provide important background information. However, few studies have considered learning with discrimination of interaural time difference (ITD). Here, learning with ITD was explored using stimuli that are more relevant to bilateral CIs than used previously. Inexperienced listeners were trained with envelope-based ITD using high-frequency amplitude-modulated tones with or without an interaural carrier frequency difference (IFD), the former to simulate asymmetrical bilateral CI insertions. All were tested with and without IFD before and after training. In most listeners, ITD thresholds improved substantially with training, not necessarily reaching asymptote after 3,000 trials. In these, the magnitude and time-course of learning was larger than anticipated from a previous study with low-frequency ITD. Learning generalized across IFD and the effect of IFD on ITD thresholds at post-test was smaller than reported previously. These results have implications for studies of bilateral CIs, such as the need to provide extensive training to avoid over-estimating any apparent 'impairment'.

Comparison of Levitt- and Zwislocki-type adaptive procedures for stimulus placement in human listeners.

The "3-down, 1-up" adaptive stimulus placement rules attributed to Levitt and Zwislocki were compared in the context of human interaural time difference discrimination, employing otherwise commonly used procedures (e.g., averaging reversals to estimate threshold). The Zwislocki rule typically accumulated over three more reversals than the Levitt rule but the rules were approximately equally efficient. This may be because the additional reversals did not provide additional information or that any additional information was countered by other factors, such as the lower theoretical asymptotic response probability (0.75 vs 0.794). Relative bias between rules was also explored with the aid of a simulation.