The effects of neural synchronization and peripheral compression on the acoustic-reflex threshold

Abstract

This study investigates the acoustic reflex threshold (ART) dependency on stimulus phase utilizing low-level reflex audiometry [Neumann et al., Audiol. Neuro-Otol. 1, 359–369 (1996)]. The goal is to obtain optimal broadband stimuli for elicitation of the acoustic reflex and to obtain objective determinations of cochlear hearing loss. Three types of tone complexes with different phase characteristics were investigated: A stimulus that compensates for basilar-membrane dispersion, thus causing a large overall neural synchrony (basilar-membrane tone complex—BMTC), the temporally inversed stimulus (iBMTC), and random-phase tone complexes (rTC). The ARTs were measured in eight normal-hearing and six hearing-impaired subjects. Five different conditions of peak amplitude and stimulus repetition rate were used for each stimulus type. The results of the present study suggest that the ART is influenced by at least two different factors: (a) the degree of synchrony of neural activity across frequency, and (b) the fast-acting compression mechanism in the cochlea that is reduced in the case of a sensorineural hearing loss. The results allow a clear distinction of the two subjects groups based on the different ART for the utilized types and conditions of the stimuli. These differences might be useful for objective recruitment detection in clinical diagnostics.

Contralateral suppression of distortion product otoacoustic emissions and the middle-ear muscle reflex in human ears

“…While CBBN was presented at levels below the ART in the present study, which is, for most subjects, similar to levels used in other studies, contribution of the MEM reflex cannot be completely ruled out. A few studies (e.g., Neumann et al, 1996;Feeney et al, 2003;Mü ller-Wehlau et al, 2005) proposed that the MEM reflex might be activated by sounds at levels below the ART, determined by the conventional middle-ear immittance test. However, investigations in patients following vestibular neurectomy, involving sectioning of MOC nerve fibers, have demonstrated that an intact MOC system is required to obtain a full suppressive effect of CAS on DPOAEs (Williams et al, 1994;Giraud et al, 1995), although the mechanism of the residual suppressive effect in those patients is to be elucidated.…”

Aural Acoustic Stapedius-Muscle Reflex Threshold Procedures to Test Human Infants and Adults

“…The present study and Keefe et al (2010) detected the ASR based on differences in the acoustic responses between the first and successive presentations of a reference click stimulus. In contrast to previous studies (Neumann et al 1996;Müller-Wehlau et al 2005), five rather than two presentations of an identical sound stimulus were used, and a tonal or BBN activator was placed between each pair of presentations (see Fig. 1).…”

“…This signal-to-noise ratio (SNR)-based test was judged more sensitive than clinical ASR tests. Müller-Wehlau et al (2005) refined this ASR technique to improve its reliability. They used a detection criterion based on the phase coherence between the pair of responses to evaluate their similarity, inasmuch as the SNR was sometimes contaminated by artifacts such as heartbeat.…”

The Effect of Contralateral Acoustic Stimulation on Spontaneous Otoacoustic Emissions

“…First, the clinical MEM reflex thresholds vary with the sensitivity of the instrumentation and the testing procedures (Gelfand 1984). Moreover, thresholds measured using clinical instruments have been consistently found to be substantially higher than those measured using a variety of experimental techniques (Neumann et al 1996;Feeney et al 2003;Guinan et al 2003;Muller-Wehlau et al 2005;Goodman and Keefe 2006). However, most studies using contralateral noise elicitors have not controlled for the MEM reflex stringently, leaving their results difficult to interpret.…”