Hearing Research最新文献

Objective: We investigated auditory working-memory using behavioural measures and electroencephalography (EEG) in adult Cochlear Implant (CI) users with varying degrees of CI performance.

Methods: 24 adult CI listeners (age: M = 61.38, SD = 12.45) performed the Sternberg auditory-digit-in-working-memory task during which EEG, accuracy, and promptness were captured. Participants were presented with 2, 4, or 6 digits at Signal-to-Noise Ratios (SNR) of 0, +5 and +10dB. They had to identify a probe stimulus as present in the preceding sequence. ANOVA models were used to compare conditions.

Results: ANOVA revealed that increasing memory load (ML) led to decreased task performance and CI performance interacted with ML and SNR. Centro-parietal alpha power increased during memory encoding but did not differ between conditions. Frontal alpha power was positively correlated with accuracy in conditions most affected by SNR (r = 0.57, r = 0.52) and theta power in conditions most affected by ML (r = 0.55, r = 0.57).

Conclusions: While parietal alpha power is modulated by the task, it is frontal alpha that relates quantitatively to sensory aspects of processing (noise) and frontal theta to memory load in this group of CI listeners.

Significance: These results suggest that alpha and theta show distinct relationships to behaviour, providing additional insight into neurocognitive (auditory working-memory) processes in CI users.

Noise-induced cochlear synaptopathy has been studied for over 25 years with no known diagnosis for this disorder in humans. This type of "hidden hearing loss" induces a loss of synapses in the inner ear but no change in audiometric thresholds. Recent studies have shown that by two months post synaptopathy-inducing noise exposure, synapses in some animal species can regenerate. Animal studies to date have focused primarily on peripheral hearing measures to diagnose ribbon synapse loss, while suggesting binaural listening deficits such as speech-reception-in-noise result from this disorder, but haven't accounted for the possible regeneration of synapses. To address this, we measured binaural physiological and behavioral function, the latter utilizing the pre-pulse inhibition of acoustic startle method, in both male and female adult guinea pigs following exposure to noise that has been shown to induce cochlear synaptopathy. Physiological measurements extended to 2 months post noise exposure to characterize any deficit and subsequent recovery. While common audiological assessments showed temporary threshold shift, reduced evoked potential amplitudes indicative of synaptopathy and measurable binaural electrophysiological hearing deficits post exposure, all measures recovered by 2 months. Suspected regeneration of synaptic ribbons occurred by 2 months post exposure and cochlear histology revealed no synaptic loss 4 months post exposure. Our results show that the same noise exposure protocol demonstrated to cause synaptic loss in prior studies causes physiological binaural processing deficits in the brainstem and that the recovery of neural binaural processing coincides with the regeneration of synapses shown in previous studies and normal binaural hearing behavior.

Originally reserved for those who are profoundly deaf, cochlear implantation is now common for people with partial hearing loss, particularly when combined with a hearing aid. This combined intervention enhances speech comprehension and sound quality when compared to electrical stimulation alone, particularly in noisy environments, but the physiological basis for the benefits is not well understood. Our long-term aim is to elucidate the underlying physiological mechanisms of this improvement, and as a first step in this process, we have investigated in normal hearing cats, the degree to which the patterns of neural activity evoked in the inferior colliculus (IC) by speech sounds in various levels of noise allows discrimination between those sounds. Neuronal responses were recorded simultaneously from 32 sites across the tonotopic axis of the IC in anaesthetised normal hearing cats (n = 7). Speech sounds were presented at 20, 40 and 60 dB SPL in quiet and with increasing levels of additive noise (signal-to-noise ratios (SNRs) -20, -15, -10, -5, 0, +5, +10, +15, +20 dB). Neural discrimination was assessed using a Euclidean measure of distance between neural responses, resulting in a function reflecting speech sound differentiation across various SNRs. Responses of IC neurons reliably encoded the speech stimuli when presented in quiet, with optimal performance when an analysis bin-width of 5-10 ms was used. Discrimination thresholds did not depend on stimulus level and were best for shorter analysis binwidths. This study sheds light on how the auditory midbrain represents speech sounds and provides baseline data with which responses to electro-acoustic speech sounds in partially deafened animals can be compared.

A comprehensive understanding of the effects of bone conduction (BC) input force is essential for elucidating BC hearing mechanisms. However, this area remains underexplored due to the inherent difficulties in controlling input forces when BC transducers are anchored to the bone. In this study, the effects of both unilateral and bilateral BC input forces were investigated using a three-dimensional finite element (FE) model of the human head, which allows precise manipulation of input forces. For unilateral input, 16 distinct directions were created by combining eight in-plane vectors with two tilt angles based on the normal direction of the input force location, and the resulting promontory velocities were compared. Although the magnitude differences between input directions remained within 10 dB, anti-resonance shifts were observed between 1 and 3 kHz. In the bilateral case, phase differences of 0°, 90°, and 180° were applied between input forces at the right and left mastoid positions, and basilar membrane velocities were compared to examine the complex interactions between input forces. These findings provide deeper insights into the effects of input force direction and phase on BC hearing, advancing the understanding of BC hearing mechanisms.