Contralateral influences of wideband inhibition on the effect of onset asynchrony as a cue for auditory grouping

Onset asynchrony is an important cue for segregating sound mixtures. A harmonic of a vowel that begins before the other components contributes less to vowel quality. This asynchrony effect can be partly reversed by accompanying the leading portion of the harmonic with an octave-higher captor tone. The original interpretation was that the captor and leading portion formed a perceptual group, but it has recently been shown that the captor effect depends on neither a common onset time nor harmonic relations with the leading portion. Instead, it has been proposed that the captor effect depends on wideband inhibition in the central auditory system. Physiological evidence suggests that such inhibition occurs both within and across ears. Experiment 1 compared the efficacy of a pure-tone captor presented in the same or opposite ear to the vowel and leading harmonic. Contralateral presentation was at least as effective as ipsilateral presentation. Experiment 2 used multicomponent captors in a more comprehensive evaluation of harmonic influences on captor efficacy. Three captors with different fundamental frequencies were used, one of which formed a consecutive harmonic series with the leading harmonic. All captors were equally effective, irrespective of the harmonic relationship. These findings support and refine the inhibitory account. © 2007 Acoustical Society of America.

Inhibitory influences on asynchrony as a cue for auditory segregation

A harmonic that begins before the other harmonics contributes less than they do to vowel quality. This reduction can be partly reversed by accompanying the leading portion with a captor tone. This effect is usually interpreted as reflecting perceptual grouping of the captor with the leading portion. Instead, it has recently been proposed that the captor effect depends on broadband inhibition within the central auditory system. A test of psychophysical predictions based on this proposal showed that captor efficacy is (a) maintained for noise-band captors, (b) absent when a captor accompanies a harmonic that continues after the vowel, and (c) maintained for 80 ms or more over a gap between captor offset and vowel onset. These findings support and refine the inhibitory account. PsycINFO Database Record © 2006 APA, all rights reserved.

Auditory training and adult rehabilitation:a critical review of the evidence

Auditory Training (AT) describes a regimen of varied listening exercises designed to improve an individual’s ability to perceive speech. The theory of AT is based on brain plasticity (the capacity of neurones in the central auditory system to alter their structure and function) in response to auditory stimulation. The practice of repeatedly listening to the speech sounds included in AT exercises is believed to drive the development of more efficient neuronal pathways, thereby improving auditory processing and speech discrimination. This critical review aims to assess whether auditory training can improve speech discrimination in adults with mild-moderate SNHL. The majority of patients attending Audiology services are adults with presbyacusis and it is therefore important to evaluate evidence of any treatment effect of AT in aural rehabilitation. Ideally this review would seek to appraise evidence of neurophysiological effects of AT so as to verify whether it does induce change in the CAS. However, due to the absence of such studies on this particular patient group, the outcome measure of speech discrimination, as a behavioural indicator of treatment effect is used instead. A review of available research was used to inform an argument for or against using AT in rehabilitative clinical practice. Six studies were identified and although the preliminary evidence indicates an improvement gained from a range of AT paradigms, the treatment effect size was modest and there remains a lack of large-sample RCTs. Future investigation into the efficacy of AT needs to employ neurophysiological studies using auditory evoked potentials in hearing-impaired adults in order to explore effects of AT on the CAS.

Asynchrony and the grouping of vowel components:captor tones revisited

Asynchrony is an important grouping cue for separating sound mixtures. A harmonic incremented in level makes a reduced contribution to vowel timbre when it begins before the other components. This contribution can be partly restored by adding a captor tone in synchrony with, and one octave above, the leading portion of the incremented harmonic [Darwin and Sutherland, Q. J. Exp. Psychol. A 36, 193-208 (1984)]. The captor is too remote to evoke adaptation in peripheral channels tuned to the incremented harmonic, and so the restoration effect is usually attributed to the grouping of the leading portion with the captor. However, results are presented that contradict this interpretation. Captor efficacy does not depend on a common onset, or harmonic relations, with the leading component. Rather, captor efficacy is influenced by frequency separation, and extends to about 1.5 oct above the leading component. Below this cutoff, the captor effect is equivalent to attenuating the leading portion of the incremented harmonic by about 6 dB. These results indicate that high-level grouping does not govern the captor effect. Instead, it is proposed that the partial restoration of the contribution of an asynchronous component to vowel timbre depends on broadband inhibition within the central auditory system. © 2006 Acoustical Society of America.

Neural population coding is optimized by discrete tuning curves

The sigmoidal tuning curve that maximizes the mutual information for a Poisson neuron, or population of Poisson neurons, is obtained. The optimal tuning curve is found to have a discrete structure that results in a quantization of the input signal. The number of quantization levels undergoes a hierarchy of phase transitions as the length of the coding window is varied. We postulate, using the mammalian auditory system as an example, that the presence of a subpopulation structure within a neural population is consistent with an optimal neural code.

A hierarchy of phase transitions in optimal neuronal coding:from binary to M-ary discrete optimal codes

We have investigated how optimal coding for neural systems changes with the time available for decoding. Optimization was in terms of maximizing information transmission. We have estimated the parameters for Poisson neurons that optimize Shannon transinformation with the assumption of rate coding. We observed a hierarchy of phase transitions from binary coding, for small decoding times, toward discrete (M-ary) coding with two, three and more quantization levels for larger decoding times. We postulate that the presence of subpopulations with specific neural characteristics could be a signiture of an optimal population coding scheme and we use the mammalian auditory system as an example.

Exploring novel auditory displays for supporting accelerated skills acquisition and enhanced performance in motorsport

This paper explores the design, development and evaluation of a novel real-time auditory display system for accelerated racing driver skills acquisition. The auditory feedback provides concurrent sensory augmentation and performance feedback using a novel target matching design. Real-time, dynamic, tonal audio feedback representing lateral G-force (a proxy for tire slip) is delivered to one ear whilst a target lateral G-force value representing the ‘limit’ of the car, to which the driver aims to drive, is panned to the driver’s other ear; tonal match across both ears signifies that the ‘limit’ has been reached. An evaluation approach was established to measure the efficacy of the audio feedback in terms of performance, workload and drivers’ assessment of self-efficacy. A preliminary human subject study was conducted in a driving simulator environment. Initial results are encouraging, indicating that there is potential for performance gain and driver confidence enhancement based on the audio feedback.