Effects of monaural stimulation by a low-frequency pure tone on binaural tinnitus
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For a subject with binaural tinnitus pitch 10 000 Hz, loudness 50 dB SPL, left ear was stimulated by a continuous pure tone 250 Hz, 125 dB SPL, 30 min. Immediately following cessation of stimulation, tinnitus completely disappeared from stimulated ear. Twenty-three min after cessation of stimulation, tinnitus was heard as a pitch 12 445 Hz. One h after stimulation, tinnitus pitch changed to 12 131 Hz; 2 h later, 11 000 Hz; 312 h later, 10 953 Hz; 5 h later returned to original pitch 10 000 Hz and stayed on to date. For a period of 23 h after stimulation, however, stimulated ear continuously heard multiple frequency tones approximately 200–800 Hz. In nonstimulated ear, immediately after cessation of stimulation, tinnitus was heard as a pitch 5000 Hz and gradually increased in pitch to 7500 Hz for 312 h. Thereafter, tinnitus pitch has been fluctuating between 9000–10 000 Hz. Tinnitus never returned to previous pitch 10 000 Hz until 16 days after stimulation. Apparent differences in recovery pattern and process between two ears were compared with a previous experiment of 500-Hz monaural stimulation.Keywords:
Monaural
Tone (literature)
The absolute sensitivity of the binaural auditory system was studied by asking subjects to discriminate tones that were truly monaural from dichotic tones that sounded monaural because of an extremely large interaural difference of intensity. Thresholds for this discrimination across the range of frequencies from 250 to 4000 Hz were achieved when the tones in the weaker channel were in the region from −45 to −50 dB relative to tones in the stronger channel. Since the monaural reference tones, as well as the stronger signals in the dichotic conditions, were chosen to be 61 dB sensation level (SL), the weakest levels for which binaural interaction could be measured appear to have been on the order of 10 to 15 dB SL.
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Dichotic listening
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A significant number (about 30%) of the binaural low-frequency medullary neurons of kangaroo rat are insensitive to interaural time differences. These neurons do not respond in a cyclic manner to the interaural time differences of any frequency within their response areas, but they are activated in a differential manner by small interaural level differences. The discharge rate to a binaural signal for one group of these neurons is greater than the discharge rate to a monaural input. For the other group, the discharge rate to monaural is greater than to binaural stimulation. In the first group, we have binaural facilitation or summation; and in the second, binaural suppression. The most important distinction between these two types, however, is that the facilitative type does not phase lock to monaural or binaural tones, whereas the suppressive type responds in synchrony to either a monaural or binaural sound. [Supported in part by NINDS Grant.]
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Facilitation
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Age-related hearing loss hampers the ability to understand speech in adverse listening conditions. This is attributed to a complex interaction of changes in the peripheral and central auditory system. One aspect that may deteriorate across the lifespan is binaural interaction. The present study investigates binaural interaction at the level of the auditory brainstem. It is hypothesized that brainstem binaural interaction deteriorates with advancing age.Forty-two subjects of various age participated in the study. Auditory brainstem responses (ABRs) were recorded using clicks and 500 Hz tone-bursts. ABRs were elicited by monaural right, monaural left, and binaural stimulation. Binaural interaction was investigated in two ways. First, grand averages of the binaural interaction component were computed for each age group. Second, wave V characteristics of the binaural ABR were compared with those of the summed left and right ABRs.Binaural interaction in the click ABR was demonstrated by shorter latencies and smaller amplitudes in the binaural compared with the summed monaural responses. For 500 Hz tone-burst ABR, no latency differences were found. However, amplitudes were significantly smaller in the binaural than summed monaural condition. An age-effect was found for 500 Hz tone-burst, but not for click ABR.Brainstem binaural interaction seems to decline with age. Interestingly, these changes seem to be stimulus-dependent.
Monaural
Auditory brainstem response
Stimulus (psychology)
Superior olivary complex
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The binaural interactions of neurons were studied in the primary auditory cortex (AI) of barbiturate-anesthetized cats with a matrix of binaural tonal stimuli varying in both interaural level differences (ILD) and average binaural level (ABL). The purpose of this study was to determine: 1) the distribution of preferred binaural combinations (PBCs) of a large population of neurons and its relationships with binaural interactions and binaural monotonicity; 2) whether monaural responses are predictive of binaural responses; and 3) whether there is a restricted set of representative binaural stimulus configurations that could effectively classify the binaural interactions. Binaural interactions were often diverse in the matrix and dependent on both ABL and ILD. Compared with previous studies, a higher proportion of mixed binaural interaction type and a lower proportion of EO/I type were found. No monaural neurons were found. Binaural responses often differed from monaural responses in the number of spikes and/or the form of the response functions. The PBCs of the majority of EO and PB neurons were in the contralateral field and midline, respectively. However, the PBCs of EE units were evenly distributed across the contralateral and ipsilateral fields. The majority of the nonmonotonic neurons responded most strongly to lower ABLs, whereas the majority of monotonic neurons responded most strongly to higher ABLs. This study demonstrated that in AI a restricted set of binaural stimulus configurations is not sufficient to reveal the binaural responses properties. Also, monaural responses are not predictive of binaural responses.
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Stimulus (psychology)
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The difference in speech identification thresholds between colocated condition (when the target and the maskers are placed at the same location) and spatially separated condition (when target and the maskers are symmetrically separated) is quantified as Spatial Release from Masking (SRM). SRM is thought to be a combination of monaural and binaural advantages arising from spatially separating the target from the maskers. Monaural contributions are from the head shadow effect whereas the binaural contributions are from processing the interaural differences between the two ears. However, the exact contributions of the monaural and binaural advantage to SRM is unknown. Here, we present data on monaural and binaural envelope processing abilities and their relationship to SRM on a large cohort of young normal hearing listeners. Monaural envelope processing ability was measured using the envelope regularity discrimination task (Moore et al., 2019). Sensitivity to ITD-envelopes was used to quantify binaural envelope processing ability. SRM was measured using coordinate response measure sentences. The relationship between SRM, envelope regularity index, and ITD thresholds along with the monaural and binaural envelope processing abilities to SRM will be discussed.
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Envelope (radar)
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The auditory system is often discussed as having monaural and binaural neurological pathways; similarly models are classified as either monaural or binaural. Psychophysical evidence of contra-aural interference (when performance with one ear is better than performance with two ears) suggests that the information used on monaural tasks (e.g., N0S0 and NmSm detection) may be carried by a binaural pathway. Binaural models often require monaural channels to predict the results of monaural tasks, but these monaural channels prevent the models from predicting contra-aural interference. This modeling work investigates the monaural information carried by a processor which is inherently binaural. The processor design makes the inclusion of monaural channels unnecessary and contra-aural interference is predicted under certain conditions. The performance of the model matches results from a variety of traditional psychophysical tasks (including discrimination of differences in overall intensity; discrimination of differences in interaural level, time and coherence; as well as detection under monaural and binaural masking conditions). Results suggest that binaural neurons contain sufficient information to explain performance on both binaural and monaural tasks. [Work supported by NIH grants R01 DC 00100 and 1 F31 DC006769-01.]
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Psychoacoustics
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We have not yet found significant intercorrelations between binaural balances, monaural balances, monaural reaction time, and magnitude estimates of loudness adaptation. Despite this, the intracorrelations for each method have been significant and moderately high. Furthermore, for group averages, the characteristics of adaptation measured by the different techniques share similarities such as the progressive decline of loudness over time, even though individuals are not consistent across methods. Recently, using the modified method of magnitude estimates with short intensity increments, we found effects on loudness estimates consistent with the models proposed for binaural balances by Weiler, Loeb, and Alluisi (1972) and Hood and Weiler (1977). Noting that magnitude judgments of loudness should occur at the highest level of the auditory system, perhaps simple magnitude estimates as evolved by Scharf's group include more of the complexities of auditory function than reaction time or balance measures.
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Binaural interaction (BI) in brainstem-auditory-evoked responses (BSERs) was defined as any deviation from the predictions of a model that assumes two independent monaural BSER generators whose outputs are additive. Brainstem-auditory-evoked responses were recorded in response to right (R) monaural, left (L) monaural, and binaural click stimuli. The monaural BSERs were added to give the model's prediction (P) of binaurally evoked BSER (P = L + R), and this trace was then subtracted from the actual binaurally evoked response (B). The resultant difference trace (d = b - p) represents the derived BI. In each of ten guinea pigs, a strong BI was present in the peak IV region (latency = 3.5 to 4.0 ms). This interaction is probably present with interaural intensity differences of up to 40 dB and interaural time differences of up to 3 ms. Preliminary studies suggest the presence of a similar phenomenon in human BSERs.
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Superior olivary complex
Auditory brainstem response
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