Band 22, Heft 3 - Special issue: Israeli Society for Auditoriy Research (ISAR): 2011 Annual Scientific Meeting

Background: A new mode of auditory stimulation has been demonstrated which is through soft tissue conduction (STC). It involves evoking auditory sensations by applying the clinical bone vibrator to the skin over soft tissue (not over bone) sites on the head and neck. Methods: This study was designed to show that stimulation by STC excites the cochlea in a way similar to that of air conduction (AC) and bone conduction (BC). Results: It is shown here that auditory nerve brainstem evoked response (ABR) thresholds in mice and in the fat sand rat to AC, to BC and to STC stimulation are all elevated following administration of drugs (salicylic acid and furosemide) which depress the cochlear amplifier. In addition, the present study brings evidence that STC stimulation is not a variant of BC since the sound pressures recorded in the occluded external auditory canal (the occlusion effect) in response to STC are significantly smaller than that to BC stimulation, though both are of equal loudness. Conclusions: This new mode, STC, therefore appears to bypass the middle ear mechanisms and consequently may contribute to auditory diagnosis.

Background: Combining stimuli arriving at both ears makes it possible to locate sounds in the environment and to better detect signals or understand speech in noise when the sound sources are separated spatially. The sensitivity of the binaural system to interaural differences in time and amplitude can be investigated by means of the binaural masking level difference (BMLD). The age at which the BMLD reaches adult levels appears to depend partly upon masker bandwidth. Less is known about the effect of masker’s level on the development of BMLD in children. In the present study we assessed the effect of masker level on the BMLD of 3rd and 5th grade skilled reading children. In view of possible binaural hearing effects in dyslexia, the BMLD of a group of 5th grade children with reading difficulties was measured. Methods: Detection thresholds of 500 Hz pure tone were measured at noise levels of 40 dBHL, 50 dBHL and 60 dBHL. Results: All subjects presented increased MLD values with the rise of noise intensity between 40 dBHL and 60 dBHL. Among the skilled readers the results showed that younger children had smaller BMLDs than older children at all masker levels. However, a significant group-by-intensity interaction indicated that although the reading disabled group had reduced BMLD values than older skilled readers at noise levels of 50 dBHL and 60 dBHL, no difference was found between their BMLD values and those of the young skilled readers at noise levels of 50 dBHL and 60 dBHL. Moreover, their BMLD values at noise level of 40 dBHL were higher than those of the 3rd grade typically reading students while no difference was found between them and 5th grade efficient readers. Conclusions: These results support the existence of both quantitative and qualitative differences in binaural hearing of children with developmental dyslexia.

Background: The aim of this study was to examine developmental trends in rate change detection of auditory rhythmic signals (repetitive sinusoidally frequency modulated tones). Methods: Two groups of children (9–10 years old and 11–12 years old) and one group of young adults performed a rate change detection (RCD) task using three types of stimuli. The rate of stimulus modulation was either constant (CR), raised by 1 Hz in the middle of the stimulus (RR1) or raised by 2 Hz in the middle of the stimulus (RR2). Results: Performance on the RCD task significantly improved with age. Also, the different stimuli showed different developmental trajectories. When the RR2 stimulus was used, results showed adult-like performance by the age of 10 years but when the RR1 stimulus was used performance continued to improve beyond 12 years of age. Conclusions: Rate change detection of repetitive sinusoidally frequency modulated tones show protracted development beyond the age of 12 years. Given evidence for abnormal processing of auditory rhythmic signals in neurodevelopmental conditions, such as dyslexia, the present methodology might help delineate the nature of these conditions.

Background: There is ample evidence showing that frequency discrimination can dramatically improve with practice. Nevertheless, the ability to generalize the learning gains to conditions that were not encountered during training is still controversial. Therefore, the purpose of the present study was to evaluate the extent of generalization to the untrained ear, to an untrained frequency (2000 Hz) and to an untrained (noisy) environment by continuing to train the generalization conditions. Methods: Twenty-one participants took part in two training phases. The first training phase included nine training sessions that consisted each of six threshold measurements of difference limen for frequency (DLF) at 1000 Hz, and a 10th testing session that consisted of three DLF thresholds at 1000 Hz. The generalization phase included four training sessions that consisted each of six DLF threshold estimates, two days at each generalization condition (each participant was trained in two out of three generalization conditions, thus the total number of participants trained in each generalization condition was 14). All DLF thresholds were estimated using a three-interval, two-alternative forced choice adaptive procedure. Results: Results showed that (1) the initial thresholds in the generalization conditions were reduced following training, and (2) new learning was observed in the subsequent training sessions suggesting that the learning was partially specific to the trained ear, frequency and environment. Conclusions: These results have important theoretical and clinical implications regarding the extent of the plasticity of the auditory system and the neural processes that underlie this plasticity.

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