Variable Venting Valve for Earmolds

The frequency response and loudness reduction characteristics of earmolds with variable venting valves (VVV) were investigated. Both side-branch and laterally vented earmolds were employed. Sound pressures were measured at 44 frequencies from 100 to 4 000 Hz in a modified HA-2 coupler with the VVV in four stages of opening: closed; ? open; ? open and 3/3 open

The effect of venting is primarily in the low frequencies. Little or no reduction in intensity is observed in the ‘speech frequency’ range and a modest amount is noted in the higher frequencies. The side-branch vented earmolds were more effective than the laterally vented earmolds. Calculated loudness reductions in phons were small. The effectiveness of the VVV, whether assessed by the frequency response or loudness reduction characteristics, is achieved within the first ? of opening: further opening has little effect. The utility of the VVV, especially to the geriatric hearing aid user, is questionable     

N1 Latencies of the Slow Auditory Evoked Potential

Several studies have been published concerning the relation between stimulus level and amplitude of the slow auditory evoked response. Little attention has, however, been given to the relation between level and latency of the N₁ component (100-200 ms). A mathematical model of such a relation is proposed based on the assumption of an exponential relationship. The model has been tested on normally hearing subjects as well as on patients with sensorineural lesions, cochlear as well as retrocochlear. The results indicate that the proposed method of evaluating the slow evoked responses offers a way of threshold extrapolation with rather good accuracy. It also appears to be useful in determining the type of hearing loss     

Critical Bandwidth in Menière's Disease

The critical bandwidth in loudness summation was estimated in 20 patients with typical Menière's disease using noise bands centered around 1 kHz. A reduction of the normal loudness difference between broad-band noise and narrow-band noise was present at all except the highest levels. Judged individually, 7 of the 20 patients appeared to have a widened critical band, but in the pooled data the size of the critical band was normal. This was the case in patients with a hearing loss <50 dB HL as well as in patients with a hearing loss ≥50 dB HL. Expressed in terms of the critical band mechanism as an internal filter system, the single filter appears to have normal bandwidth but the interaction between adjacent filters is defective. The anatomical localisation of this interaction is discussed.     

Cross-Modal Matching of Loudness and Brightness as a Recruitment Test for Hearing-Impaired Children

Normal 5-year-olds have been reported to be able, in a simple game situation, to match brightness to loudness in the same way as a control group of adults. This study investigated supplanting the normal ear in an alternate binaural loudness balance test (ABLB) with the visual modality, as a recruitment test designed especially for bilaterally hearing-impaired children. The results of normal 10-year-olds, with simulated hearing losses, suggest that category scaling was adopted naturally as a simplifying strategy in preference to ratio scaling (absolute judgements). No proportional increase in the matching function slope was evident, despite the amount of recruitment measured with an ABLB. The instructions needed to combat this strategy render the test unfeasible with hearing-impaired children.     

Enhanced pure-tone pitch discrimination among persons with autism but not Asperger syndrome

Persons with Autism spectrum disorders (ASD) display atypical perceptual processing in visual and auditory tasks. In vision, Bertone, Mottron, Jelenic, and Faubert (2005) found that enhanced and diminished visual processing is linked to the level of neural complexity required to process stimuli, as proposed in the neural complexity hypothesis. Based on these findings, Samson, Mottron, Jemel, Belin, and Ciocca (2006) proposed to extend the neural complexity hypothesis to the auditory modality. They hypothesized that persons with ASD should display enhanced performance for simple tones that are processed in primary auditory cortical regions, but diminished performance for complex tones that require additional processing in associative auditory regions, in comparison to typically developing individuals. To assess this hypothesis, we designed four auditory discrimination experiments targeting pitch, non-vocal and vocal timbre, and loudness. Stimuli consisted of spectro-temporally simple and complex tones. The participants were adolescents and young adults with autism, Asperger syndrome, and typical developmental histories, all with IQs in the normal range. Consistent with the neural complexity hypothesis and enhanced perceptual functioning model of ASD (Mottron, Dawson, Soulières, Hubert, & Burack, 2006), the participants with autism, but not with Asperger syndrome, displayed enhanced pitch discrimination for simple tones. However, no discrimination-thresholds differences were found between the participants with ASD and the typically developing persons across spectrally and temporally complex conditions. These findings indicate that enhanced pure-tone pitch discrimination may be a cognitive correlate of speech-delay among persons with ASD. However, auditory discrimination among this group does not appear to be directly contingent on the spectro-temporal complexity of the stimuli.     

Influence of stimulation rate and loudness growth on modulation detection and intensity discrimination in cochlear implant users

In cochlear implants (CIs), increasing the stimulation rate typically increases the electric dynamic range (DR), mostly by reducing audibility thresholds. While CI users’ intensity resolution has been shown to be fairly constant across stimulation rates, high rates have been shown to weaken modulation sensitivity, especially at low listening levels. In this study, modulation detection thresholds (MDTs) were measured in five CI users for a range of stimulation rates (250–2000 pulses per second) and modulation frequencies (5–100 Hz) at 8 stimulation levels that spanned the DR (loudness-balanced across stimulation rates). Intensity difference limens (IDLs) were measured for the same stimulation rates and levels used for modulation detection. For all modulation frequencies, modulation sensitivity was generally poorer at low levels and at higher stimulation rates. CI users were sensitive to modulation frequency only at relatively high levels. Similarly, IDLs were poorer at low levels and at high stimulation rates. When compared directly in terms of relative amplitude, IDLs were generally better than MDTs at low levels. Differences in loudness growth between dynamic and steady stimuli might explain level-dependent differences between MDTs and IDLs. The slower loudness growth associated with high stimulation rates might explain the poorer MDTs and IDLs with high rates. In general, high stimulation rates provided no advantage in intensity resolution and a disadvantage in modulation sensitivity.     

Development of Sound Localization

Perceptual sound localization is determined from differences in time and loudness of signals arriving separately at bilateral ears, with the time difference being the more important one. The author examined the development of sound lateralization using a self-recording device developed by Sato. It measures the sensitivity of sound lateralization on the basis of time and loudness differences separately. Subjects were 59 children aged 2 to 18 years and 12 adults who were audiologically and neurologically normal. Sound stimulus was 500Hz continuous band noise. (1) The testable rate was increased in children older than the age of 4, and all children over 7 years of age could be tested. (2) Children over 4 years of age could lateralize sound on the basis of time difference. Sensitivity to time differences improved rapidly, showing a steep curve, in children from the ages of 4 to 6, and then increased slowly until adulthood. (3) Sensitivity to loudness differences increased and standard deviation decreased with age. There is a possibility that children aged 4 can discriminate loudness difference almost as well as adults.     

Electrocochleography and experimentally induced loudness recruitment

Summary The relationship between changes in loudness and the cochlear whole-nerve potential following experimentally produced deafness was studied in an animal model. Reaction time of a subject's response to an auditory stimulus has been shown to be an index of loudness in human experiments and has been adapted to nonhuman primates. In a series of experiments, four macaque monkeys were operantly conditioned to respond to 8-kHz tones over a range of 0–80 dB SPL, and their reaction times to pure tone stimuli were measured. Whole-nerve cochlear action potentials were recorded from chronic inner-ear electrodes. The relationship between behavioral and electrical measures of loudness recruitment were examined in animals with both temporary and permanent noise-induced hearing loss.Loudness recruitment was demonstrated experimentally after a 1-h exposure to a high-intensity 8-kHz octave band of noise. Excellent agreement was observed between the reaction time function and the action potential input-output function at intervals of 0.5, 12, 24, 48, and 84 h after exposure.Permanent hearing loss was produced in some of these animals by a much longer duration of exposure to the 8-kHz octave band of noise. Recruitment was observed in both the behavioral and the electrical measures. Histological studies of these damaged cochleas revealed primarily outer hair cell destruction, with a relative sparing of inner hair cells and nerve supply. The findings of this study are interpreted as strong support for the clinical electrocochleogram as an objective indicator of the presence of loudness recruitment.This investigation was supported by research grants NS-05077, NS-05065 and NS-10854, Program Project grant NS-05786, training grant NS-05679, and Postdoctoral fellowship SF 11 NS-2423-03 to J.E.P. from the National Institutes of Health     

Loudness balance between electric and acoustic stimulation

Binaural loudness balance between electric and acoustic stimulation is obtained in auditory brainstem implant listeners who had substantial acoustic hearing in one ear. The data are well described by a linear relationship between acoustic decibels and electric microamps. Based upon this linear relationship, we propose an exponential model of loudness growth in electric stimulation. The exponential model predicts that the loudness growth function can be determined solely by the threshold and the uncomfortable loudness level in electric stimulation. This prediction is consistent with previous psychophysical data on loudness functions. Implications of this finding for speech processor designs are discussed.     

Functional neuroimaging in hearing research and audiology

The various methods of medical imaging are essential for many diagnostic issues in clinical routine, e.g., for the diagnostics and localisation of tumorous diseases, or for the clarification of other lesions in the central nervous system. In addition to these classical roles both positron emission tomography (PET) and magnetic resonance imaging (MRI) allow for the investigation of functional processes in the human brain, when used in a specific way. The last 25 years have seen great progress, especially with respect to functional MRI, in terms of the available experimental paradigms as well as the data analysis strategies, so that a directed investigation of neurophysiological correlates of psychoacoustic performance is possible. This covers fundamental measures of sound perception like loudness and pitch, specific audiological symptoms like tinnitus, which often accompanies hearing disorders, but it also includes experiments on speech perception or on virtual acoustic environments. One important aspect common to many auditory neuroimaging studies is the central question at what stage in the human auditory pathway the sensory coding of the incoming sound is transformed into a universal and context-dependent perceptual representation, which is the basis for what we hear. This overview summarises findings from the literature as well as a few studies from our lab, to discuss the possibilities and the limits of the adoption of functional neuroimaging methods in audiology. Up to this stage, most auditory neuroimaging studies have investigated basic processes in normal hearing listeners. However, the hitherto existing results suggest that the methods of auditory functional neuroimaging – possibly complemented by electrophysiological methods like EEG and MEG – have a great potential to contribute to a deeper understanding of the processes and the impact of hearing disorders.