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Objective: The objective of this study was to investigate the localization ability of bilateral cochlear implant (BiCI) users for virtual sound sources produced over a limited loudspeaker arrangement. Design: Ten BiCI users and 10 normal-hearing subjects participated in listening tests in which amplitude- and time-panned virtual sound sources were produced over a limited loudspeaker setup with varying azimuth angles. Three stimuli were utilized: speech, band-passed pink noise between 20 Hz and 1 kHz, and band-passed pink noise between 1 kHz and 8 kHz. The data were collected via a two-alternative forced-choice procedure and used to calculate the minimum audible angle (MAA) of each subject, which was subsequently compared to the results of previous studies in which real sound sources were employed. Result The median MAAs of the amplitude-panned speech, low-frequency pink noise, and high-frequency pink noise stimuli for the BiCI group were calculated to be 20 degrees, 38 degrees, and 12 degrees, respectively. For the time-panned stimuli, the MAAs of the BiCI group for all three stimuli were calculated to be close to the upper limit of the listening test. Conclusions: The computed MAAs of the BiCI group for amplitude-panned speech were marginally larger than BiCI users' previously reported MAAs for real sound sources, whereas their computed MAAs for the time-panned stimuli were significantly larger. Subsequent statistical analysis indicated a statistically significant difference in the performances of the BiCI group in localizing the amplitude-panned sources and the time-panned sources. It follows that time-panning over limited loudspeaker arrangements may not be a useful clinical tool, whereas amplitude-panning utilizing such a setup may be further explored as such. Additionally, a comparison with the patient demographics indicated correlations between the results and the patients' age at time of diagnoses and the time passed between date of diagnosis and their implant surgeries.

Failure in the structural maintenance of the hair cell stereocilia bundle and ribbon synapse causes hearing loss. Here, we have studied how ER stress elicits hair cell pathology, using mouse models with inactivation of Manf (mesencephalic astrocytederived neurotrophic factor), encoding an ER-homeostasispromoting protein. From hearing onset, Manf deficiency caused disarray of the outer hair cell stereocilia bundle and reduced cochlear sound amplification capability throughout the tonotopic axis. In high-frequency outer hair cells, the pathology ended in molecular changes in the stereocilia taper region and in strong stereocilia fusion. In high-frequency inner hair cells, Manf deficiency degraded ribbon synapses. The altered phenotype strongly depended on the mouse genetic background. Altogether, the failure in the ER homeostasis maintenance induced early-onset stereociliopathy and synaptopathy and accelerated the effect of genetic causes driving age-related hearing loss. Correspondingly, MANF mutation in a human patient induced severe sensorineural hearing loss from a young age onward. Thus, we present MANF as a novel protein and ER stress as a mechanism that regulate auditory hair cell maintenance in both mice and humans.

Sisäkorvaistutehoito sopii sekä synnynnäisen vaikea-asteisen kuulovian että etenevän kuulovian hoidoksi. Istutteella voidaan saavuttaa hyvä puheentunnistuskyky vaikea-asteisessa kuulonalenemassa. Hoito on osoitettu kustannusvaikuttavaksi kaikissa ikäryhmissä. Nuorimmat potilaat ovat olleet 8–10 kuukauden ja vanhimmat yli 80 vuoden ikäisiä. Vanhusväestössä on paljon vaikea-asteisesta kuuloviasta kärsiviä potilaita, jotka hyötyisivät istutehoidosta. Heitä tulisi ohjata nykyistä aktiivisemmin leikkausarvioon.

Väestön ikääntyessä kuulonalenemien esiintyvyys ja tarve vaikuttavaan kuulonkuntoutukseen kasvavat. Hyvän yleiskäsityksen kuulosta antavat äänieriön hiljaisuudessa tehtävät perustutkimukset, äänesaudiometria ja puheaudiometria. Ne eivät kuitenkaan välttämättä kuvasta kuulonaleneman aiheuttamaa haittaa hälyisissä tilanteissa. Uuden suomenkielisen hälylausetestin avulla voidaan tutkia aiempaa paremmin aikuisten kuntoutuspotilaiden kuulonvaraista selviämistä arjessa. Suomenkielisen lasten hälypuhetestin validointi on meneillään.

English summary

The effect of the sound incidence angle on loudness was investigated for fifteen listeners who matched the loudness of sounds coming from five different incidence angles in the horizontal plane to that of the same sound with frontal incidence. The stimuli were presented via binaural synthesis by using head-related transfer functions measured for an artificial head. The results, which exhibited marked individual differences, show that loudness depends on the direction from which a sound reaches the listener. The average results suggest a relatively simple rule for combining the two signals at the ears of an artificial head for binaural loudness predictions.

Udgivelsesdato: Maj 2006 The effect of sound incidence angle on loudness was investigated using real sound sources positioned in an anechoic chamber. Eight normal-hearing listeners produced loudness matches between a frontal reference location and seven sources placed at other directions, both in the horizontal and median planes. Matches were obtained via a two-interval, adaptive forced-choice (2AFC) procedure for three center frequencies (0.4, 1 and 5 kHz) and two overall levels (45 and 65 dB SPL). The results showed that loudness is not constant over sound incidence angles, with directional sensitivity varying over a range of up to 10 dB, exhibiting considerable frequency dependence, but only minor effects of overall level. The pattern of results varied substantially between subjects, but was largely accounted for by variations in individual head-related transfer functions. Modeling of binaural loudness based on the at-ear signals favored a sound-power summation model, according to which the maximum binaural gain is only 3dB, over competing models based on larger gains, or on the summation of monaural loudness indices.

In an earlier study (1), the loudness of directional sounds presented in an anechoic chamber was investigated by having listeners make loudness matches to a frontal reference source. The listeners' individual head-related transfer functions (HRTFs) were also measured, in an attempt to model the binaural loudness summation of the at-ear signals. Even though the effects of HRTFs were taken into account, considerable individual differences in the binaural summation of loudness remained. In order to create conditions in which the directional at-ear changes were identical for all participants, the present experiment employed 'generic' HRTFs to create directional sounds via binaural synthesis. When inspecting the results of the listening tests, however, large individual differences were still evident, as in the earlier study. The generality of this finding was further corroborated by running an independent, inexperienced sample of ten participants exclusively being exposed to the present generic HRTFs. Despite the individual differences, the average results suggest a relatively simple rule for combining the binaural input when carrying out acoustical measurements using an artificial head. That is particularly useful when attempting to predict loudness for dichotic listening situations, as they typically result from real sound sources positioned in space.

Loudness, the perceived intensity of sound, is a fundamental attribute in psychoacoustics. An immense body of literature on loudness has been accumulated, and based on the reported findings, models for predicting loudness from monophonic, acoustical measurements of sound pressure have been developed. The research and modeling of loudness have mainly been concerned with the temporal and spectral aspects of sounds, while the spatial aspects have mostly been overlooked.This PhD thesis investigates the spatial aspects of loudness perception, namely, how does the direction from which a sound reaches the listener affect its perceived loudness. The results obtained in a series of listening experiments show that loudness depends considerably on direction for a variety of sound stimuli. Furthermore,these directional dependencies could be largely accounted for by determining binaural at-ear exposures, individually for each listener. The results of the thesis were used for developing a binaural loudness model. This model is applicable to acoustical measurements made with artificial heads, commonly used in a variety of applications, ranging from the assessment of noise annoyance to evaluating product soundquality and the fidelity of multichannel sound reproduction systems.

Even though there is a vast body of literature on spatial hearing, little is known on how the location of a sound source affects its loudness. The pertinent research on head-related transfer functions(HRTFs) primarily deals with issues of localization and spatial discriminability. The literature on binaural loudness summation, on the other hand, focuses on a highly artificial paradigm according to which unnatural combinations of sound pressure levels(such as monotic-diotic comparisons) are presented to listeners via headphones. In order to reconcile these two approaches, we recently started a series of experiments determining the effect of sound incidence angle on loudness[1,2,3,4]. The basic experiment to be reported on here was conducted in an anechoic chamber, in which loudspeakers were mounted to present sounds from a number of directions both in the horizontal, and median planes. The subject’s task was to produce a loudness match to a frontal reference location, and matches were obtained via a two-interval adaptive forced-choice procedure. Narrow-band noises were used, in order to investigate the frequency-specific effects of direction on loudness. Furthermore, individual HRTFs were measured for each incidence angle, in order to relate the changes in actual at-ear exposure to the observed changes in loudness as a function of sound incidence. Combining the listening-test data with the physical measurements, an attempt was made to model the binaural summation underlying the directional loudness matches.

The effect of incidence angle on loudness was investigated for wideband and reverberant sounds. In an adaptive procedure, five listeners matched the loudness of a sound coming from five incidence angles in the horizontal plane to that of the same sound with frontal incidence. The stimuli were presented to the listeners via individual binaural synthesis. The results confirm that loudness depends on sound incidence angle, as it does for narrow-band, anechoic sounds. The directional effects, however, were attenuated with the wideband and reverberant stimuli used in the present investigation.

The effect of sound incidence angle on loudness is investigated in this study using binaural synthesis. Individual head-related transfer functions (HRTFs) and headphone equalization are used to present narrow-band noises from different directions to listeners. Their task is to match the loudness of these stimuli in an adaptive procedure to a reference noise in front of the listeners. The results are compared to an earlier investigation with the same experimental design in a real sound field. Based on the results the role of the individual HRTFs in loudness judgments is inspected, and finally, binaural loudness summation of signals presented to the two ears is examined.