Volume 24, Issue 3

Hereditary hearing loss affects a significant proportion of the hearing impaired, with genetic mutations estimated to be responsible for its etiology in over 50% of this population. The methods for molecular diagnostics are changing as a result of the transition from linkage analysis to next generation sequencing to identify the genes responsible for hearing loss in affected families. In this review, we summarize the attitudes of the hearing impaired towards genetic testing, the latest techniques for identifying mutations, and provide a comprehensive list of the mutations found in the Israeli Jewish hearing-impaired population.

Background: Soft tissue conduction (STC) is a recently described mode of auditory stimulation in which vibrations induced by a clinical bone vibrator applied to soft tissue sites on the head, neck, and thorax of human subjects reach the cochlea and elicit auditory sensation. In humans, STC stimulation interacts with air conduction stimulation and with bone conduction (BC) stimulation in several ways, e.g., mutual masking. Methods: This study investigated whether mutual masking between STC and BC stimulation can be demonstrated in an experimental animal. In fat sand rats, auditory nerve and brainstem evoked response to BC stimulation was recorded in the presence of noise masking presented by STC and vice versa. Results: STC successfully masked BC, and BC also masked STC responses. Conclusions: Mutual masking, now demonstrated in animals, paves the way for animal experiments to clarify the pathway between the STC stimulation sites and the cochlea.

Background: Older adults manifest difficulties in speech perception, especially when speech is accompanied by noise or when speech is rapid. Several explanations have been suggested to account for age-related changes in speech perception, such as changes in hearing sensitivity or a more general decline in cognitive functioning. The purpose of the present study was to directly examine the relative contribution of hearing sensitivity and perceptual and cognitive factors in the understanding of age-related differences in speech perception under difficult conditions. Methods: Eighty-nine healthy participants with normal hearing thresholds, age 21–82 years, were tested for speech perception under four conditions: quiet, speech noise, white noise, and time-compressed speech at 60% compression rate. As all participants had age-normal hearing, absolute thresholds were tested for click trains, 1 kHz 15-ms duration pure tone, 1 kHz 50-ms duration pure tone, and 1.8 kHz 15-ms duration pure tone, which are relatively short and discriminative for hearing ability. Cognitive ability was examined using the Wechsler Adult Intelligence Scale (Third Edition) matrices and digit span. Results: When words were presented against a quiet background or against white noise, speech perception was not significantly affected by aging, although in the latter case, increased thresholds predicted poorer speech perception. However, when words were presented against a background of speech noise or when speech was time-compressed at a 60% rate, age significantly predicted a decline in speech perception, even after controlling for hearing thresholds and cognitive functioning. Conclusions: Hearing threshold for short sounds is the major factor for predicting speech perception in background noise, across age, due to changes in hearing sensitivity or in temporal resolution. For the adult and aging population with preserved cognitive ability, cognitive functioning does not predict decline in speech perception.

Background: Several studies suggest that auditory perception in general and the perception of speech in noise in particular continue to develop until late childhood or early adolescence. It remains unclear, however, whether this prolonged development results from the maturation of the cognitive factors associated with the performance of auditory tasks or from the slow development of auditory sensory processing. Methods: We investigated the perception of monosyllabic words embedded in white noise in Hebrew-speaking school-age children and adults. Results: Although identification thresholds did not become adult-like until 11 years of age, we found no evidence linking this prolonged development to non-sensory factors associated with performance consistency. Conclusions: Therefore, we suggest that similar to the development of amplitude and frequency modulation detection thresholds, this protracted development is related to the maturation of auditory sensory processing.

Background: The present study examined whether the reported age-related decline in auditory temporal resolution is specific to the temporal domain or rather reflects a general decline in auditory perception, including the stimulus intensity domain. Methods: The performance of 89 healthy participants aged between 21 and 82 years with normal hearing was tested on a variety of psychophysical tasks, where discrimination was based either on the temporal or on the intensity domains. Stimulus levels for all tasks were 40 dB SL (corrected for threshold). Participants were also tested on two cognitive tasks: Wechsler Adult Intelligence Scale, Third Edition, matrices and digit span. Results: Findings indicate that age was significantly negatively correlated with performance on three of the temporal resolution tasks, namely, dichotic temporal-order judgment, spectral temporal-order judgment, and gap detection, but not on the intensity discrimination task, thus emphasizing the specificity of the age-related decline to the auditory temporal domain. Conclusions: The overall results suggest that age-related changes in auditory perception are specific to the temporal domain, even when controlling for hearing sensitivity and cognitive ability, and are not reflected in other aspects of non-temporal perception, such as intensity discrimination.

Background: Soft tissue conduction (STC), a recently described mode of auditory stimulation elicited when the clinical bone vibrator is applied to skin sites over the head, neck, and thorax, complements air conduction (AC) and bone conduction (BC), elicited by the same vibrator. The study assessed skull bone vibrations induced during STC and BC stimulation. Methods: The experiments were conducted on fat sand rats. Thresholds of auditory nerve brainstem evoked responses (ABRs) were recorded and compared to the lowest-intensity sound stimuli that elicited vibrations at the bony vestibule of the inner ear detected by a laser Doppler vibrometer. Results: Vibrations were detected during BC but not during STC stimulation. ABR was recorded to both STC and to BC stimulation. Conclusions: Low-intensity STC stimulation does not induce vibrations of the inner ear, showing that STC apparently does not involve mechanisms based on vibrations of bone.

Background: Implantation at a young age enables exposure to language and speech during the critical age for language acquisition. Long duration of auditory deprivation may lead to less optimal results. Methods: A retrospective review of cases was performed. A young girl with congenital bilateral profound sensorineural hearing loss received her first cochlear implant on the right side at the age of 2½ years and successfully developed good speech and language. At the age of 10 years, explantation had to be performed, and as reimplantation could not be done on the same side, the implantation was done on the left ear, which had never received auditory stimulation. Two age-matched girls with bilateral sequential implantation, in whom the second sound-deprived ear was implanted after a long duration, were studied as well. Results: A year after implantation, in two of the cases there was very good speech perception, even in noise. In one case, the second ear never attained the ability to understand speech. Conclusions: These results can be explained in light of recent findings that early unilateral stimulation can result in bilateral representation in the auditory cortex.