Daniel Rowan

Identification of auditory cues utilized in human echolocation - objective measurement results

We present objective measurements of source-to-ear responses obtained in a previously established human echolocation experimental paradigm. We identify the auditory cues that allow humans to perform echolocation tasks in that specific scenario and we discuss the salience of those cues with respect to more complex scenarios. This work allows us to formulate an experimental protocol for conducting more detailed and informative subjective listening test experiments in human echolocation.

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 3000 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’. Sumario El advenimiento de los implantes cocleares bilaterales (CI) ha aumentado el interés en aprender sobre tareas binauriculares, y los estudios en sujetos oyentes normales han aportado importante información pertinente. Sin embargo, pocos estudios han considerado el estudio del aprendizaje con base en la discriminación de diferencias interauriculares de tiempo (ITD). Aquí, el aprendizaje con ITD fue explorado utilizando estímulos más relevantes para los CI bilaterales que los usados previamente. Se entrenó a oyentes sin experiencia con una ITD con base en envolventes que comprendían tonos de alta frecuencia de amplitud modulada, con o sin diferencia interauricular de la frecuencia portadora (IFD), esta última para simular inserciones bilaterales asimétricas de CI. Todos fueron evaluados con y sin IFD antes y después del entrenamiento, sin alcanzar necesariamente la asíntota después de 3000 intentos. En ellos, la magnitud y el tiempo del aprendizaje fue mayor de lo anticipado en un estudio con una ITD de baja frecuencia. El aprendizaje en general en todas las IFD y el efecto de la IFD sobre los umbrales de ITD después de la prueba fue similar a los reportes previos. Estos resultados tienen implicaciones en los estudios de CI bilaterales, tales como la necesidad de proveer amplio entrenamiento para evitar la sobre-estimación de cualquier ‘impedimento’ aparente.

Learning to discriminate interaural time differences at low and high frequencies.

This study investigated learning, in normal-hearing adults, associated with training (i.e. repeated practice) on the discrimination of ongoing interaural time difference (ITD). Specifically, the study addressed an apparent disparity in the conclusions of previous studies, which reported training-induced learning at high frequencies but not at low frequencies. Twenty normal-hearing adults were trained with either low- or high-frequency stimuli, associated with comparable asymptotic thresholds, or served as untrained controls. Overall, trained listeners learnt more than controls and over multiple sessions. The magnitudes and time-courses of learning with the low- and high-frequency stimuli were similar. While this is inconsistent with the conclusion of a previous study with low-frequency ITD, this previous conclusion may not be justified by the results reported. Generalization of learning across frequency was found, although more detailed investigations of stimulus-specific learning are warranted. Overall, the results are consistent with the notion that ongoing ITD processing is functionally uniform across frequency. These results may have implications for clinical populations, such as users of bilateral cochlear implants.

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.

Fit for the frontline? A focus group exploration of auditory tasks carried out by infantry and combat support personnel

In order to preserve their operational effectiveness and ultimately their survival, military personnel must be able to detect important acoustic signals and maintain situational awareness. The possession of sufficient hearing ability to perform job-specific auditory tasks is defined as auditory fitness for duty (AFFD). Pure tone audiometry (PTA) is used to assess AFFD in the UK military; however, it is unclear whether PTA is able to accurately predict performance on job-specific auditory tasks. The aim of the current study was to gather information about auditory tasks carried out by infantry personnel on the frontline and the environment these tasks are performed in. The study consisted of 16 focus group interviews with an average of five participants per group. Eighty British army personnel were recruited from five infantry regiments. The focus group guideline included seven open-ended questions designed to elicit information about the auditory tasks performed on operational duty. Content analysis of the data resulted in two main themes: (1) the auditory tasks personnel are expected to perform and (2) situations where personnel felt their hearing ability was reduced. Auditory tasks were divided into subthemes of sound detection, speech communication and sound localization. Reasons for reduced performance included background noise, hearing protection and attention difficulties. The current study provided an important and novel insight to the complex auditory environment experienced by British infantry personnel and identified 17 auditory tasks carried out by personnel on operational duties. These auditory tasks will be used to inform the development of a functional AFFD test for infantry personnel.

The detection of ‘virtual’ objects using echoes by humans: spectral cues

Abstract 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. HighlightsSighted and blind listeners had to detect virtual objects using echoes.Most listeners could use changes in spectral shape across a wide bandwidth.Changes in spectral shape are diminished by room reverberation.Good high‐frequency hearing is generally important for echolocation.The optimal echo‐generating stimulus will probably depend on the task.

Fit for the frontline? Identification of mission-critical auditory tasks (MCATs) carried out by infantry and combat-support personnel

The ability to listen to commands in noisy environments and understand acoustic signals, while maintaining situational awareness, is an important skill for military personnel and can be critical for mission success. Seventeen auditory tasks carried out by British infantry and combat-support personnel were identified through a series of focus groups conducted by Bevis et al. For military personnel, these auditory tasks are termed mission-critical auditory tasks (MCATs) if they are carried in out in a military-specific environment and have a negative consequence when performed below a specified level. A questionnaire study was conducted to find out which of the auditory tasks identified by Bevis et al. satisfy the characteristics of an MCAT. Seventy-nine British infantry and combat-support personnel from four regiments across the South of England participated. For each auditory task participants indicated: 1) the consequences of poor performance on the task, 2) who performs the task, and 3) how frequently the task is carried out. The data were analysed to determine which tasks are carried out by which personnel, which have the most negative consequences when performed poorly, and which are performed the most frequently. This resulted in a list of 9 MCATs (7 speech communication tasks, 1 sound localization task, and 1 sound detection task) that should be prioritised for representation in a measure of auditory fitness for duty (AFFD) for these personnel. Incorporating MCATs in AFFD measures will help to ensure that personnel have the necessary auditory skills for safe and effective deployment on operational duties.

Investigations of mammalian echolocation

Active echolocation is a sensory modality possessed by a variety of mammals and is used for the identification, classification and localization of objects. A multi stage model of the bat echolocation process has been used with recordings of rotated disks to plot frequency spectrums of the signals reaching each of the bats’ ears. Recordings from objects made within the human audible frequency range have also been made for use in psychoacoustic experiments aimed at validating preliminary studies that have shown some human ability to localize objects using echolocation.

Development and evaluation of the British English Coordinate Response Measure Speech-In-Noise Test as an occupational hearing assessment tool

Abstract 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.

Reference data for the multi-centre study of a synchronised bilateral cochlear implant system

Abstracts of the British Society of Audiology annual conference (incorporating the Experimental and Clinical Short papers meetings)s of the British Society of Audiology annual conference (incorporating the Experimental and Clinical Short papers meetings) September xx–xx, 2012, NIHR National Biomedical Research Unit in Hearing, Nottingham Trent University, UK Fortnum H, Hall D, Smith S (eds)