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PubMed2004

Optical imaging of binaural interaction in multiple fields of the guinea pig auditory cortex.

Locating the source of a sound is an important function of the auditory system and interaural intensity differences are one of the most important cues. To study the functional pathways of sound localisation processing in the auditory cortex, activity in multiple fields of the guinea pig auditory cortex during stimulation with interaural intensity differences was studied using optical imaging with a voltage-sensitive dye. Of the auditory core (primary and dorsocaudal) and the belt fields which surround them, the posterior and ventroposterior belt fields were the most sensitive to interaural intensity differences. This suggests that the caudal pathway of the auditory cortex is involved in sound localisation.

Acoustic Stimulation↗
PubMed1986

An introduction to unilateral sensorineural hearing loss in children.

This paper offers a general review of literature on issues pertinent to unilateral hearing loss in children. The paper focuses on such areas as demographic considerations, the importance of binaural hearing, the effects of noise on speech recognition, learning and educational factors, and auditory deprivation. It is concluded that there is sufficient evidence to suspect that children with unilateral sensorineural hearing loss can experience complications in communication and education. Finally, this paper presents the description of a research plan used in our study on unilateral sensorineural hearing loss in children.

Achievement↗
PubMed1986

The unilaterally hearing-impaired child: a final comment.

This paper offers a summary of the general findings from a study on unilateral sensorineural hearing loss as well as some comments with regard to possible reasons for outcome. Additional comments are provided on the management of unilaterally hearing-impaired children, future directions for research, and an emphasis on the limitations and interpretations of this investigation.

Achievement↗
PubMed1987

Insertion gain repeatability versus loudspeaker location: you want me to put my loudspeaker where?

The traditional 0 degree (straight-ahead) location of the loudspeaker during insertion gain measurements is a poor choice, based on theoretical considerations, from the standpoint of measurement repeatability. In a series of experiments, we were able to demonstrate that a location 45 degrees to the side, or 45 degrees up and 45 degrees to the side, provided a much more repeatable measurement of basically the same insertion gain response.

Acoustics↗
PubMed1987

A correction for converting 2 cm3 coupler responses to insertion responses for custom in-the-ear nondirectional hearing aids.

A correction for custom in-the-ear nondirectional hearing aids is obtained for converting a frequency response measured using a 2 cm3 coupler to an insertion response, approximating that measured using a manikin and ear simulator. The results are compared to those of a previous published study. The methods used for obtaining the responses make use of a signal analyzer with discrete Fourier transform capabilities.

Acoustics↗
PubMed1991

The timing of the processes underlying lateralization: psychophysical and evoked potential measures.

This article describes a technique to measure binaural integration time. A binaural noise with an interaural time difference of 0.8 msec was presented in three conditions: alone, with intervening noise that was identical between the two ears, or with uncorrelated intervening noise. Both behavioral responses and evoked potentials were recorded. When the stimulus was presented in a quiet background, it was accurately detected and lateralized with durations as short as 2 msec. The N1 peak of the evoked potential occurred at approximately 90 msec. When the stimulus occurred as a brief change in an ongoing correlated binaural noise, a duration of 10 msec was necessary before the sound could be accurately lateralized or an evoked potential elicited. The N1 peak occurred at approximately 120 msec. When the stimulus occurred as a change in an ongoing uncorrelated binaural noise, a duration of 60 msec was necessary for the subject to lateralize the stimulus and for an evoked potential to be elicited. The N1 peak occurred at about 130 msec. These results suggest that a period of approximately 60 msec is required to detect the correlation of an ongoing binaural noise and that a somewhat shorter period is necessary to track changes in a sound source that has already been lateralized. The simplicity of this technique makes it an attractive tool for assessing central auditory function.

Acoustic Stimulation↗
PubMed1996

Physiological plasticity in the auditory system and its possible relevance to hearing aid use, deprivation effects, and acclimatization.

Alterations in the physiological and/or the anatomical properties of the central auditory system (neural plasticity) can be induced by unilateral or bilateral sensorineural hearing loss, auditory stimulation, and conditioning in which sounds are used as conditioned stimuli. These types of neural plasticity have implications for hearing aid use, acclimatization, and deprivation effects. The occurrence of hearing-loss-induced plasticity suggests that the organization of the central auditory system may be altered by the time a hearing aid is fitted. The success of hearing aids may depend, therefore, on how the auditory system responds to the reintroduction of certain sounds by amplification. For example, enhanced auditory stimulation provided by hearing aids may induce "secondary" plasticity in the auditory system, which might contribute to acclimatization and/or deprivation effects. Such functional changes might be further modulated by reinforcing responses to reintroduced sounds using conditioning techniques. This article reviews relevant literature on auditory system plasticity--drawn largely from animal research--with the goal of providing insight into possible mechanisms of acclimatization and deprivation effects.

Brain↗
PubMed2002

Sound-direction identification, interaural time delay discrimination, and speech intelligibility advantages in noise for a bilateral cochlear implant user.

OBJECTIVES: To characterize some of the benefits available from using two cochlear implants compared with 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. METHODS: Sound-direction ID in the horizontal plane was tested with a bilateral cochlear implant user. The subject was tested both unilaterally and bilaterally using two independent behind-the-ear ESPRIT (Cochlear Ltd.) processors, as well as bilaterally using custom research processors. Pink noise bursts were presented using an 11-loudspeaker array spanning the subject's frontal 180 degrees arc in an anechoic room. After each burst, the subject was asked to identify which loudspeaker had produced the sound. No explicit training, and no feedback were given. Presentation levels were nominally at 70 dB SPL, except for a repeat experiment using the clinical devices where the presentation levels were reduced to 60 dB SPL to avoid activation of the devices' automatic gain control (AGC) circuits. Overall presentation levels were randomly varied by +/- 3 dB. For the research processor, a "low-update-rate" and a "high-update-rate" strategy were tested. Direct measurements of ITD just noticeable differences (JNDs) were made using a 3 AFC paradigm targeting 70% correct performance on the psychometric function. Stimuli included simple, low-rate electrical pulse trains as well as high-rate pulse trains modulated at 100 Hz. Speech data comparing monaural and binaural performance in noise were also collected with both low, and high update-rate strategies on the research processors. Open-set sentences were presented from directly in front of the subject and competing multi-talker babble noise was presented from the same loudspeaker, or from a loudspeaker placed 90 degrees to the left or right of the subject. RESULTS: For the sound-direction ID task, monaural performance using the clinical devices showed large mean absolute errors of 81 degrees and 73 degrees, with standard deviations (averaged across all 11 loud-speakers) of 10 degrees and 17 degrees, for left and right ears, respectively. Fore bilateral device use at a presentation level of 70 dB SPL, the mean error improved to about 16 degrees with an average standard deviation of 18 degrees. When the presentation level was decreased to 60 dB SPL to avoid activation of the automatic gain control (AGC) circuits in the clinical processors, the mean response error improved further to 8 degrees with a standard deviation of 13 degrees. Further tests with the custom research processors, which had a higher stimulation rate and did not include AGCs, showed comparable response errors: around 8 or 9 degrees and a standard deviation of about 11 degrees for both update rates. The best ITD JNDs measured for this subject were between 350 to 400 microsec 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. For spatially coincident speech and noise, listening with both ears showed similar results to listening with either side alone when loudness summation was compensated for. No significant differences were observed between binaural results for high and low update-rates in any test configuration. Only for monaural listening in one test configuration did the high rate show a small significant improvement over the low rate. CONCLUSION: 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.

Adult↗
PubMed2002

Auditory cortical response patterns to multiple rhythms of AM sound.

OBJECTIVE: Multiple amplitude modulation (AM) of a tone results in a time series with a complex structure of envelope fluctuations. In this study the cortical responses elicited by such an auditory stimulus were investigated. It was hypothesized that the auditory cortex responds simultaneously with different patterns of activity corresponding to the different rhythm of periodical stimulus fluctuations. The relations of these response patterns to either steady-state responses (SSR) in the 40 Hz range or the transient slow auditory evoked responses were investigated. DESIGN: Auditory evoked magnetic fields were recorded from the left temporal cortex of nine healthy humans in response to 250 Hz tones that were amplitude modulated with the sum of two sinusoids of 38 and 40 Hz. The stimulus was presented continuously to the subject's right ear at the intensity of 70 dB sensation level. In addition, the responses to 250 Hz tone-burst stimuli with duration of 20, 50, 100, and 200 msec, respectively, were recorded. The tone-bursts were presented at an inter-stimulus interval (ISI) of 0.5 sec, which was equivalent to the slowest rhythm of the multiple-AM stimulus. Magnetic source analysis was applied to all elicited waveforms. RESULTS: From all subjects SSR at 38 and 40 Hz were clearly recognizable and were superimposed by a periodical response pattern corresponding to 2 Hz stimulus envelope fluctuations. A positive peak with latency of 70 msec was the mostly pronounced response to tone-burst stimulation at the ISI of 0.5 sec and resembles the low-frequency response pattern to the AM stimulus. The N1-P2 complex showed an almost complete suppression at 0.5 sec ISI. In contrast, it was the most prominent evoked response activity when using a longer ISI of 3 sec. Source locations in overlapping areas were estimated for the SSR in the 40 Hz range, the prominent peak of low-frequency response to the AM stimulus, and the P1 peak at tone-burst stimulation, respectively. These were separated from the N1 source location by about 0.5 cm in anterior and 0.5 cm in medial direction. CONCLUSION: As a result of multiple AM the stimulus signal envelope fluctuates with frequencies of 2 Hz and around 40 Hz. The auditory cortex responds to this stimulus with different response patterns. Both modulation signals at 38 and 40 Hz were almost linearly represented as steady-state responses. The evoked response patterns to stimulus fluctuations at low-frequency rhythm resemble the slow cortical auditory evoked responses. The 2 Hz stimulus rhythm is perceived as loudness fluctuation, and 40 Hz modulation is perceived as a rough sound. It is assumed that the different cortical representations correspond to both types of perception of the complex AM sound.

Adult↗
PubMed1991

A method to automate radiological surveys: the Ultrasonic Ranging and Data System.

The Ultrasonic Ranging and Data System (USRADS) was developed to allow radiation exposure rate data and positional information to be simultaneously collected, stored, and analyzed in a manner more efficient than conventional survey techniques. USRADS is field portable using ultrasonics to locate a field surveyor on a site and radiofrequency to transmit data. Surveyor position (e.g., measurement location within 10 cm) and an integrated instrument measurement are recorded and stored once each second in a microcomputer. Operational experience indicates that the system results in collection of greater quantity and higher quality of radiological data with less effort in data transcription and analysis and only slightly more field effort compared to conventional manual methods.

Data Collection↗
PubMed1982

The use of temporal and amplitude cues by schizophrenics, psychiatric controls, and aged normals in auditory lateralization.

The present study investigated the ability of paranoid and nonparanoid schizophrenics, psychiatric controls, and aged controls to use temporal and amplitude cues to make judgments about the direction of auditory stimuli on an auditory lateralization task. Twelve subjects in each group were tested on three lateralization conditions: temporal--fixed, temporal--shifted, and amplitude. The subjects' task was to identify the apparent direction (left or right) of a train of clicks presented binaurally through headphones. In the temporal conditions interaural click onset differences provided the lateralization cues, while in the amplitude condition interaural amplitude differences provided the cues. In the temporal--fixed condition, onset asynchrony was constant for the duration of each stimulus. In the temporal--shifted condition, onset asynchrony was introduced midway through each stimulus presentation. A forced-choice random staircase method was used to determine each subject's 70 per cent correct response threshold. Results indicated that paranoids had particular difficulty with the temporal--fixed condition relative to the temporal--shifted condition. The opposite was true for the nonparanoids. Both control groups showed no significant difference in performance on the two temporal conditions. Psychiatric controls performed significantly better than aged controls in both the fixed and shifted conditions. There were no significant differences among groups on the amplitude condition. The data were discussed in terms of schizophrenics' clinical symptoms and previous perceptual research with schizophrenics.

Acoustic Stimulation↗
PubMed1985

Self-report of the frequency and phenomenology of verbal hallucinations.

This study was an assessment of several parameters of verbal hallucinations ("voices") based on the self-report of 52 hallucinating psychiatric patients. These subjects were asked to estimate the frequency of their hallucinations and to rate phenomenological aspects (loudness, clarity, location, reality) of their most recent hallucination. Each parameter was assessed with two visual analogue scales which differed in their wording of the dimension. Results showed that the reliability of the subjects' estimates on the parameters differed greatly. Clarity was most reliably reported and reality was least reliably reported. Historical notions that schizophrenics characteristically perceive external "voices" and that such "voices" are perceived as more real were not supported. There was a significant negative correlation between the perceived location and the perceived clarity of hallucinations. No significant differences in mean parameter scores were found between two groups of subjects, schizophrenics and affective psychotics.

Adult↗
PubMed1999

A patient-benefit evaluation of unilateral congenital conductive hearing loss presenting in adulthood: should it be repaired?

OBJECTIVE: To evaluate subjective and objective outcomes of surgical therapy in congenital conductive hearing loss (HL) presenting in adulthood. The impact of hearing restoration on quality of life (QOL) for these patients may differ from those with acquired HL. STUDY DESIGN: Retrospective review of five patients treated surgically. METHODS: Standard audiometry was completed. Patients completed a subjective questionnaire as well as subjective (open-set) questions. A seven-point Likert scale was used for closed-set responses with 1 representing the worst possible outcome and 7 being best. RESULTS: The average four-frequency improvements in pure-tone average and air-bone gap were 18 dB (range, 7-29 dB) and 16 dB (range, 2-30 dB), respectively. An average score was obtained for each closed-set question. The highest-scoring items were for overall improvement of QOL (average score, 6), followed by perceived improvement in hearing (average score, 5.6). Other positive responses were improved ability to use the telephone (four of five patients) and improved localization of sound (four of five patients). Negative subjective responses included prolonged dysequilibrium in two of five, prolonged adjustment period in three, and dysgeusia in one patient. CONCLUSION: Important components of outcome are likely to escape our review if only objective measures are used to evaluate surgical outcomes. These results suggest that improved hearing in this population provides specific improvements in lifestyle and is perceived as a significant improvement in overall QOL.

Adult↗
PubMed2001

Estimating sound source distance with and without vision.

BACKGROUND: Visual capture is an important perceptual phenomenon in which the spatial location of a visual target influences the perceived location of a related auditory target. Little is known about visual capture in a distance dimension. METHODS: Two groups of listeners judged the apparent distances of five loudspeaker sound sources, extending from 1 to 5 m. In one group, each listener was allowed to view the loudspeaker array. In the second group, listeners were blindfolded for the duration of the experiment. RESULTS: No visual capture effects were observed. Instead, the addition of vision was found to both improve distance judgment accuracy and lower judgment variability compared with the auditory-only stimulus. Auditory-only accuracy was found to substantially improve over the course of the experiment, however. CONCLUSIONS: Visual capture in distance is perhaps less general than suggested by past research, a result that has important implications for the display of spatial layout under conditions where vision is either missing or degraded.

Adolescent↗