EAP recordings in Ineraid patients- correlations with psychophysical measurements and possible implications for patient fitting.
Zimmerling and Hochmair

Intracochlear measurements of electrically evoked compound action potentials (EAP) can help fit cochlear implants in very young children. For coding strategies that employ a moderate stimulation rate of 250 cycles per second, correlations between EAP data and behavioral responses (threshold and maximum confortable levels) have been found. However, some commonly used stimulation strategies such as CIS employ stimulation rates of 2,000 cycles per second or more, and it is important to establish possible correlations at these higher rates. This study used direct electrical measurements of neural activity in the cochlea instead of making indirect measurements with a telemetry system. This was possible because the subjects used the Ineraid device, whose intracochlear electrodes can be accessed directly through a transcutaneous plug. Significant correlations between behavioral and physiological responses at high stimulation rates were found, but only after introduction of a rate-correction factor which corrected for disparities due to temporal integration.

Relationship between intensity and reaction time in normal hearing infants and adults.
Leibold and Werner

Understanding loudness perception in infants may provide clues about the mechanisms underlying developmental changes in auditory sensitivity. Additionally, understanding loudness growth in infants may be useful to better diagnose and manage hearing loss in this population. Because infants cannot express how loud something sounds to them in a readily interpretable way, alternative ways of measuring loudness must be used. The present study measured reaction time (RT, which has been shown to vary inversely with loudness), in normal hearing children and adults. Mean RT decreased with increasing intensity in both groups. Examination of mean RT as a function of sound intensity suggests that infants= curves may be steeper than adults=, but considerable variability between subjects was apparent. To probe this question further, future studies will have to reduce the variability of RT measurements.

Patients Utilizing a Hearing Aid and a Cochlear Implant: Speech Perception and Localization
Tyler et al.

Over the years, the average speech perception scores obtained by implant recipients have increased. As speech perception scores have improved, the criteria for implant candidacy have become more lenient. Now patients with some residual hearing are regarded as good candidates for a cochlear implant, if other criteria for implantation are met. One result of this change is that some patients using an implant in one ear also will use a hearing aid in the other ear. This pilot study aims to document speech perception and localization abilities in patients who use a cochlear implant in one ear and a hearing aid in the other ear. Three such patients were tested on word and sentence recognition, and localization tasks. Two of the three patients showed a binaural advantage when speech and noise were presented from the front (the third patient was the one who received least benefit from his hearing aid alone), and two of the three patients also showed a localization advantage when using both devices. More research is needed to compare the potential advantages of binaural fitting with two similar devices to those that can be obtained with one cochlear implant and one hearing aid.

Auditory steady-state responses to exponential modulation envelopes.
John et al.

Recording auditory steady state responses to modulated tones can provide an objective estimation of hearing thresholds in patients who cannot be reliably tested using behavioral audiometry. The speed at which the thresholds can be determined depends in part upon the size of the response, which must be recognized as significantly different from the background noise of the recording. When using brief tonebursts to evoke transient auditory brainstem responses a compromise must be reached: More rapid onsets lead to larger responses but also decrease the frequency specificity of the stimuli. This study examined the steady-state responses evoked by tones modulated with exponential envelopes. When tones were amplitude-modulated with exponential envelopes based on sinN, the amplitude and latency of the steady-state response increased significantly with increasing N. Using exponential envelopes with N greater than 1 should considerably shorten the time needed for responses to become significant when using steady-state responses in objective audiometry.

Maturation of mismatch negativity in typically developing infants and pre school children.
Morr et al.

Few reliable methods are available for assessing auditory discrimination abilities in infants and young children. Since normal speech and language development require the discrimination of the fine acoustic features of speech, it is important to find a reliable method that can be used to examine these abilities. The recording of event-related potentials (ERPs) is one possible method that could be used to evaluate the neural mechanisms underlying a child=s ability to process fine-grained differences in auditory stimuli. The mismatch negativity (MMN) is an ERP component that is an index of largely attention-independent, automatic discrimination of auditory information. The aims of this study were to determine whether an adult-like MMN can be
reliably elicited in typically-developing awake infants and pre-school children, and if so to examine whether maturational changes exist in MMN latency and amplitude. Negativities were reliably elicited in the infants and preschoolers across all ages using a 1000 Hz tone as the standard stimulus and a 2000 Hz tone as the oddball (this did not happen, though, when the oddball stimulus was a 1200 Hz tone). A significant negative correlation was observed between
age and latency, but not for age and amplitude for this negativity. While there is convincing
evidence that the negativity elicited in this study is an immature MMN, the results from these experiments suggest that the MMN component has limited use as a clinical tool at this time for infants and young children.

Sound-direction identification, interaural time delay discrimination and speech
intelligibility advantages in noise for a bilateral cocblear implant user.
Richard van Hoesel,. Richard Ramsden and Martin O'Driscol

Although cochlear implants (CI=s) are becoming increasingly common among people with hearing loss, devices are presently fitted unilaterally in the majority of cases. The clinical practice of bilateral implantation has recently gained some interest, but whether it becomes a standard procedure will depend largely on whether an adequate benefit can be demonstrated to warrant the additional expense and risks. In order to characterize some of the benefits available from using two cochlear implants compared to just one, sound-direction identification (ID) abilities, sensitivity to interaural time delays (ITDs) and speech intelligibility in noise were measured for a bilateral multi-channel cochlear implant user. The subject showed a large binaural advantage in sound direction identification, with mean errors of 73 to 81 degrees in the monaural condition, but only 8 to 16 degrees in the binaural condition. The best just noticeable differences in ITD for this subject were between 350 to 400 microseconds for simple low-rate pulse trains. Speech results showed a substantial headshadow advantage for bilateral device use when speech and noise were spatially separated, but little evidence of binaural unmasking. In summary, results show that even if interaural time delay cues are not well coded or perceived, bilateral implants can offer important advantages, both for speech in noise as well as for sound-direction identification.

Middle ear dynamic characteristics in patients with otosclerosis.
Zhao et al.

Otosclerosis is an inherited disorder of bone growth that mainly affects the stapes and the
bony labyrinth of the cochlea. The disease is characterised by resorption of the normally hard bone and its replacement with newer, softer bone tissue which is highly vascular and spongy, and which can eventually turn into a dense sclerotic mass. These pathological changes prevent the stapes from vibrating in response to sound waves and, thus lead to progressive conductive hearing loss. Recently a new system has been developed to measure the middle ear dynamic characteristics under physiological conditions using a high sweep-frequency resolution impedance meter (SFI), which records sound pressure in dB SPL across a sweeping stimulus frequency instead of immittance measures in the conventional impedance meter. A three dimensional output shows the sound pressure curves versus both probe frequency and external auditory meatus static pressure. Therefore, the SF1 provides more information on middle ear dynamic characteristics, including the resonance frequency and the sound pressure change (ASPL), which reflects the magnitude of the tympanic membrane volume displacement at the resonance frequency and represents an index of middle ear mobility. The aim of this study was to investigate the middle ear dynamic characteristics in patients with otosclerosis using the SF1 test and conventional tympanometry, and also to evaluate the diagnostic efficiency of the SF1 test for otosclerosis. On comparison of the results of SF1 with conventional tympanometry, a significantly higher percentage of abnormal stiffness was found when using the SF1 test than that when using conventional tympanometry. The present findings confirm the advantage of the SF1 test over conventional tympanometry in detecting middle ear status and mechanics in patients with otosclerosis.

 

Spondee recognition in a two-talker masker and a speech-shaped noise masker in adults and children
Hall et al.

It is well known that many aspects of human auditory perception show substantialdevelopmental effects over the first decade of life. However, the reasons for poorer auditory performance in children are not entirely clear and have been explained by sensory factors, or by non-peripheral factors such as attention or experience with language. The present study attempted to investigate auditory development for a spondee recognition paradigm likely to be influenced by non-sensory factors. The key element was the use of a masker composed of two talkers, which has been shown to be a more effective masker than white noise of the same intensity. It is of interest to gather information on this question because similar listening conditions are common in everyday environments, and it is unknown whether they pose any special difficulties for young listeners. The objective of the study was to examine developmental effects for Aperceptual@ masking due a two-talker masker. Both continuous and gated maskers were employed in order to determine the importance of masker continuity for perceptual masking. The results for the continuous masker indicated higher thresholds for the two-talker masker than for the speech-shaped noise masker. This effect was greater in a group of 5-10 year old children than in a group of adults. In the gated masking condition, the greater masking effect associated with the two-talker masker was either diminished (children) or eliminated (adults). This result suggests that grade school children may be at a greater disadvantage than adults in real-life environments in which a target signal must be separated from competing speech information.