Sound Source Selection Based on Head Movements in Natural Group Conversation.

To optimally improve signal-to-noise ratio in noisy environments, a hearing assistance device must correctly identify what is signal and what is noise. Many of the biosignal-based approaches to solving this question are themselves subject to noise, but head angle is an overt behavior that may be possible to capture in practical devices in the real world. Previous orientation studies have demonstrated that head angle is systematically related to listening target; our study aimed to examine whether this relationship is sufficiently reliable to be used in group conversations where participants may be seated in different layouts and the listener is free to turn their body as well as their head.

Negative impacts from latency masked by noise in simulated beamforming.

Those experiencing hearing loss face severe challenges in perceiving speech in noisy situations such as a busy restaurant or cafe. There are many factors contributing to this deficit including decreased audibility, reduced frequency resolution, and decline in temporal synchrony across the auditory system. Some hearing assistive devices implement beamforming in which multiple microphones are used in combination to attenuate surrounding noise while the target speaker is left unattenuated.

A framework for designing head-related transfer function distance metrics that capture localization perception.

Linear comparisons can fail to describe perceptual differences between head-related transfer functions (HRTFs), reducing their utility for perceptual tests, HRTF selection methods, and prediction algorithms. This work introduces a machine learning framework for constructing a perceptual error metric that is aligned with performance in human sound localization. A neural network is first trained to predict measurement locations from a large database of HRTFs and then fine-tuned with perceptual data.

Speech intelligibility with various head-related transfer functions: A computational modelling approach.

Speech intelligibility (SI) is known to be affected by the relative spatial position between target and interferers. The benefit of a spatial separation is, along with other factors, related to the head-related transfer function (HRTF). The HRTF is individually different and thus, the cues that affect SI might also be different.

Conversation in small groups: Speaking and listening strategies depend on the complexities of the environment and group.

Many conversations in our day-to-day lives are held in noisy environments - impeding comprehension, and in groups - taxing auditory attention-switching processes. These situations are particularly challenging for older adults in cognitive and sensory decline. In noisy environments, a variety of extra-linguistic strategies are available to speakers and listeners to facilitate communication, but while models of language account for the impact of context on word choice, there has been little consideration of the impact of context on extra-linguistic behaviour.

Angle-Dependent Distortions in the Perceptual Topology of Acoustic Space.

By moving sounds around the head and asking listeners to report which ones moved more, it was found that sound sources at the side of a listener must move at least twice as much as ones in front to be judged as moving the same amount. A relative expansion of space in the front and compression at the side has consequences for spatial perception of moving sounds by both static and moving listeners. An accompanying prediction that the apparent location of static sound sources ought to also be distorted agrees with previous work and suggests that this is a general perceptual phenomenon that is not limited to moving signals.

Psychophysical evidence for auditory motion parallax.

Distance is important: From an ecological perspective, knowledge about the distance to either prey or predator is vital. However, the distance of an unknown sound source is particularly difficult to assess, especially in anechoic environments. In vision, changes in perspective resulting from observer motion produce a reliable, consistent, and unambiguous impression of depth known as motion parallax.

Real-time estimation of horizontal gaze angle by saccade integration using in-ear electrooculography.

The manuscript proposes and evaluates a real-time algorithm for estimating eye gaze angle based solely on single-channel electrooculography (EOG), which can be obtained directly from the ear canal using conductive ear moulds. In contrast to conventional high-pass filtering, we used an algorithm that calculates absolute eye gaze angle via statistical analysis of detected saccades. The estimated eye positions of the new algorithm were still noisy.

The minimum monitoring signal-to-noise ratio for off-axis signals and its implications for directional hearing aids.

The signal-to-noise ratio (SNR) benefit of hearing aid directional microphones is dependent on the angle of the listener relative to the target, something that can change drastically and dynamically in a typical group conversation. When a new target signal is significantly off-axis, directional microphones lead to slower target orientation, more complex movements, and more reversals. This raises the question of whether there is an optimal design for directional microphones.

Egocentric and allocentric representations in auditory cortex.

A key function of the brain is to provide a stable representation of an object's location in the world. In hearing, sound azimuth and elevation are encoded by neurons throughout the auditory system, and auditory cortex is necessary for sound localization. However, the coordinate frame in which neurons represent sound space remains undefined: classical spatial receptive fields in head-fixed subjects can be explained either by sensitivity to sound source location relative to the head (egocentric) or relative to the world (allocentric encoding).

Auditory compensation for head rotation is incomplete.

Hearing is confronted by a similar problem to vision when the observer moves. The image motion that is created remains ambiguous until the observer knows the velocity of eye and/or head. One way the visual system solves this problem is to use motor commands, proprioception, and vestibular information.

The Effects of Hearing Impairment, Age, and Hearing Aids on the Use of Self-Motion for Determining Front/Back Location.

Background: There are two cues that listeners use to disambiguate the front/back location of a sound source: high-frequency spectral cues associated with the head and pinnae, and self-motion-related binaural cues. The use of these cues can be compromised in listeners with hearing impairment and users of hearing aids.

Purpose: To determine how age, hearing impairment, and the use of hearing aids affect a listener's ability to determine front from back based on both self-motion and spectral cues.

In vitro characterization of cationic copolymer-complexed recombinant human butyrylcholinesterase.

Effective use of exogenous human BChE as a bioscavenger for organophosphorus toxicants (OPs) is hindered by its limited availability and rapid clearance. Complexes made from recombinant human BChE (rhBChE) and copolymers may be useful in addressing these problems. We used in vitro approaches to compare enzyme activity, sensitivity to inhibition, stability and bioscavenging capacity of free enzyme and copolymer-rhBChE complexes (C-BCs) based on one of nine different copolymers, from combinations of three molecular weights (MW) of poly-L-lysine (PLL; high MW, 30-70 kDa; medium MW, 15-30 kDa; low MW, 4-15 kDa) and three grafting ratios of poly(ethylene glycol) (PEG; 2:1, 10:1, 20:1).

Biomimetic direction of arrival estimation for resolving front-back confusions in hearing aids.

Sound sources at the same angle in front or behind a two-microphone array (e.g., bilateral hearing aids) produce the same time delay and two estimates for the direction of arrival: A front-back confusion.

The moving minimum audible angle is smaller during self motion than during source motion.

our heads rotate in three axes and move in three dimensions, constantly varying the spectral and binaural cues at the ear drums. In spite of this motion, static sound sources in the world are typically perceived as stable objects. This argues that the auditory system-in a manner not unlike the vestibulo-ocular reflex-works to compensate for self motion and stabilize our sensory representation of the world.

The effect of hearing aid microphone mode on performance in an auditory orienting task.

Objectives: Although directional microphones on a hearing aid provide a signal-to-noise ratio benefit in a noisy background, the amount of benefit is dependent on how close the signal of interest is to the front of the user. It is assumed that when the signal of interest is off-axis, users can reorient themselves to the signal to make use of the directional microphones to improve signal-to-noise ratio. The present study tested this assumption by measuring the head-orienting behavior of bilaterally fit hearing-impaired individuals with their microphones set to omnidirectional and directional modes.

The contribution of head movement to the externalization and internalization of sounds.

Background: When stimuli are presented over headphones, they are typically perceived as internalized; i.e., they appear to emanate from inside the head.

The internal representation of vowel spectra investigated using behavioral response-triggered averaging.

Listeners presented with noise were asked to press a key whenever they heard the vowels [a] or [i:]. The noise had a random spectrum, with levels in 60 frequency bins changing every 0.5 s.

The role of head movements and signal spectrum in an auditory front/back illusion.

We used a dynamic auditory spatial illusion to investigate the role of self-motion and acoustics in shaping our spatial percept of the environment. Using motion capture, we smoothly moved a sound source around listeners as a function of their own head movements. A lowpass filtered sound behind a listener that moved in the direction it would have moved if it had been located in the front was perceived as statically located in front.

Undirected head movements of listeners with asymmetrical hearing impairment during a speech-in-noise task.

It has long been understood that the level of a sound at the ear is dependent on head orientation, but the way in which listeners move their heads during listening has remained largely unstudied. Given the task of understanding a speech signal in the presence of a simultaneous noise, listeners could potentially use head orientation to either maximize the level of the signal in their better ear, or to maximize the signal-to-noise ratio in their better ear. To establish what head orientation strategy listeners use in a speech comprehension task, we used an infrared motion-tracking system to measure the head movements of 36 listeners with large (>16 dB) differences in hearing threshold between their left and right ears.

Auditory and visual orienting responses in listeners with and without hearing-impairment.

Head movements are intimately involved in sound localization and may provide information that could aid an impaired auditory system. Using an infrared camera system, head position and orientation was measured for 17 normal-hearing and 14 hearing-impaired listeners seated at the center of a ring of loudspeakers. Listeners were asked to orient their heads as quickly as was comfortable toward a sequence of visual targets, or were blindfolded and asked to orient toward a sequence of loudspeakers playing a short sentence.

Patterned tone sequences reveal non-linear interactions in auditory spectrotemporal receptive fields in the inferior colliculus.

Linear measures of auditory receptive fields do not always fully account for a neuron's response to spectrotemporally-complex signals such as frequency-modulated sweeps (FM) and communication sounds. A possible source of this discrepancy is cross-frequency interactions, common response properties which may be missed by linear receptive fields but captured using two-tone masking. Using a patterned tonal sequence that included a balanced set of all possible tone-to-tone transitions, we have here combined the spectrotemporal receptive field with two-tone masking to measure spectrotemporal response maps (STRM).

On the prediction of sweep rate and directional selectivity for FM sounds from two-tone interactions in the inferior colliculus.

Two-tone stimuli have traditionally been used to reveal regions of inhibition in auditory spectral receptive fields, particularly for neurons with low spontaneous rates. These techniques reveal how different frequencies excite or suppress the response to an excitatory frequency of a cell, but have often been assessed at a fixed masker-probe time interval. We used a variation of this methodology to determine whether two-tone spectrotemporal interactions can account for rate-dependent directional selectivity for frequency modulations (FM) in the mustached bat inferior colliculus (IC).

Directional selectivity for FM sweeps in the suprageniculate nucleus of the mustached bat medial geniculate body.

Mustached bats emit echolocation and communication calls containing both constant frequency (CF) and frequency-modulated (FM) components. Previously we found that 86% of neurons in the ventral division of the external nucleus of the inferior colliculus (ICXv) were directionally selective for linear FM sweeps and that selectivity was dependent on sweep rate. The ICXv projects to the suprageniculate nucleus (Sg) of the medial geniculate body.