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PubMed1992

Effects of interaural speech-recognition differences on binaural advantage for speech in noise.

The relationship between interaural differences in speech-recognition performance and binaural advantage for speech in noise was studied. Subjects were five hearing-impaired listeners with symmetrical pure-tone air-conduction audiograms and significant interaural differences in speech recognition. All subjects repeated nonsense syllables in the presence of competing noise in monaural and binaural conditions. Binaural advantage was calculated as the difference in signal-to-noise ratio that afforded 50 percent correct performance between the monaural and binaural conditions. The results were diverse. Although the majority of the subjects retained some degree of binaural advantage, a conclusive relationship between interaural differences in speech recognition and binaural advantage could not be established. The implications for binaural hearing aid fittings are discussed.

Aged↗
PubMed1983

Noise-induced cochlear damage assessed using electrophysiological and morphological criteria: an examination of the equal energy principle.

Cochlear damage immediately following exposure to continuous pure tones of varying intensity and duration was assessed in anaesthetized guinea pigs. Indices of damage used were elevation of N1 thresholds and severity of swelling of the afferent dendrites beneath the inner hair cell. The results were not wholly consistent with the assumptions of the equal energy principle. Longer duration exposures resulted in greater N1 threshold elevation and more severe swelling of dendrites than short exposures of the same total energy.

Animals↗
PubMed2006

Neural rate and timing cues for detection and discrimination of amplitude-modulated tones in the awake rabbit inferior colliculus.

Neural responses to amplitude-modulated (AM) tones in the unanesthetized rabbit inferior colliculus (IC) were studied in an effort to establish explicit relationships between physiological and psychophysical measures of temporal envelope processing. Specifically, responses to variations in modulation depth (m) at the cell's best modulation frequency, with and without modulation maskers, were quantified in terms of average rate and synchronization to the envelope over the entire perceptual dynamic range of depths. Statistically significant variations in the metrics were used to define neural AM detection and discrimination thresholds. Synchrony emerged at modulation depths comparable with psychophysical AM detection sensitivities in some neurons, whereas the lowest rate-based neural thresholds could not account for psychoacoustical thresholds. The majority of rate thresholds (85%) were -10 dB or higher (in 20 log m), and 16% of the population exhibited no systematic dependence of average rate on m. Neural thresholds for AM detection did not decrease systematically at higher SPLs (as observed psychophysically): thresholds remained constant or increased with level for most cells tested at multiple sound-pressure levels (SPLs). At depths higher than the rate-based detection threshold, some rate modulation-depth functions were sufficiently steep with respect to the across-trial variability of the rate to predict depth discrimination thresholds as low as 1 dB (comparable with the psychophysics). Synchrony, on the other hand, did not vary systematically with m in many cells at high modulation depths. A simple computational model was extended to reproduce several features of the modulation frequency and depth dependence of both transient and sustained pure-tone responders.

Acoustic Stimulation↗
PubMed1997

Coding for auditory space in the nucleus of the brachium of the inferior colliculus in the ferret.

Coding for auditory space in the nucleus of the brachium of the inferior colliculus in the ferret. J. Neurophysiol. 78: 2717-2731, 1997. The nucleus of the brachium of the inferior colliculus (BIN) projects topographically to the deeper layers of the superior colliculus (SC), which contain a two-dimensional map of auditory space. In this study, we have used broadband stimuli presented in the free field to investigate how auditory space is represented in the BIN of the ferret. Response latencies and temporal firing patterns were comparable with those in the SC, and both properties showed some variation with stimulus location. We obtained spatial response profiles at two sound levels (5-15 and 25-35 dB above unit threshold). A large proportion of azimuth profiles (41% in the suprathreshold condition, 80% in the near-threshold condition) presented a single peak, indicating that they were tuned to single regions in space. For some of these units, the preferred speaker position varied considerably with sound level. The remaining units showed predominantly either broad "hemifield" or spatially ambiguous "bilobed" response profiles. At suprathreshold sound levels, the preferred azimuths of the tuned cells were ordered topographically along the rostrocaudal axis of the BIN, although this representation is considerably more scattered than that in the SC. In contrast to the SC, we observed no systematic variation in the distribution of near-threshold best azimuths, which were instead concentrated around the interaural axis in the contralateral hemifield. The azimuth tuning of individual units in the BIN was generally broader at both sound levels than that in the SC. Many units also were tuned for the elevation of the sound source (48% for supra-, 77% for near-threshold stimulation), but there was no evidence for topographic order in the distribution of preferred elevations within the BIN. These results suggest that the BIN sends inputs to the SC that are already selective for sound azimuth and elevation and that show some degree of topographic order for sound azimuth. These inputs then presumably are sharpened and their topography refined by a mechanism that is likely to involve convergence of other inputs and activity-dependent fine tuning of terminal connections, to result in a precise two-dimensional map of auditory space in the SC.

Acoustic Stimulation↗
PubMedDate not supplied

Event-related potentials in an auditory oddball situation in the rat.

Evoked potentials were recorded from the auditory cortex of both freely moving and anesthetized rats when deviant sounds were presented in a homogenous series of standard sounds (oddball condition). A component of the evoked response to deviant sounds, the mismatch negativity (MMN), may underlie the ability to discriminate acoustic differences, a fundamental aspect of auditory perception. Whereas most MMN studies in animals have been done using simple sounds, this study involved a more complex set of sounds (synthesized vowels). The freely moving rats had previously undergone behavioral training in which they learned to respond differentially to these sounds. Although we found little evidence in this preparation for the typical, epidurally recorded, MMN response, a significant difference between deviant and standard evoked potentials was noted for the freely moving animals in the 100-200 ms range following stimulus onset. No such difference was found in the anesthetized animals.

Animals↗
PubMed1989

Nonlinguistic auditory capabilities in aphasia.

Nonlinguistic auditory capabilities were assessed through psychophysical tests in 11 left-CVA aphasic, four right-CVA nonaphasic, and eight normal male subjects selected from the same age group. The tests included frequency discrimination, gap detection, gap discrimination, frequency sweep discrimination, assessment of the magnitude of the frequency uncertainty effect in the detectability of tones in noise, and assessment of frequency selectivity through simultaneous masked thresholds. Results of these tests were compared to measures of auditory comprehension obtained from the Boston Diagnostic Aphasia Examination, the Porch Index of Communicative Ability, and the Token Test. Nonlinguistic auditory performance of the three subject groups differed significantly from each other. For the left-CVA subjects, frequency sweep discrimination, frequency discrimination, and the frequency uncertainty effect in tone-in-noise detection were the best predictors of verbal auditory comprehension. The right-CVA subjects displayed marked deficits with regard to all pitch-related tests. The findings stress the importance of considering the presence of nonlinguistic auditory dysfunctions when evaluating linguistic auditory capabilities in aphasia.

Adult↗
PubMed2003

Auditory temporal order discrimination and backward recognition masking in adults with dyslexia.

The ability of 20 adult dyslexic readers to extract frequency information from successive tone pairs was compared with that of IQ-matched controls using temporal order discrimination and auditory backward recognition masking (ABRM) tasks. In both paradigms, the interstimulus interval (ISI) between tones in a pair was either short (20 ms) or long (200 ms). Temporal order discrimination was better for both groups of listeners at long than at short ISIs, but no group differences in performance were observed at either ISI. Performance on the ABRM task was also better at long than at short ISIs and was influenced by variability in masker frequency and by the spectral proximity of target and masker. The only significant group difference was found in one condition of the ABRM task when the target-masker interval was 200 ms, but this difference was not reliable when the measure was of optimal performance. Moderate correlations were observed between auditory thresholds and phonological skill for the sample as a whole and within the dyslexic and control groups. However, although a small subgroup of dyslexic listeners with poor phonology was characterized by elevated thresholds across the auditory tasks, evidence for an association between auditory and phonological processing skills was weakened by the finding of a subgroup of control listeners with poor auditory processing and normal phonological processing skills.

Adult↗
PubMed2002

A comparison between vocal reaction time and word recognition measures of children with APD and age-matched peers using auditory word discrimination test.

The purpose of this study was to investigate the possibility of improving speech recognition testing sensitivity in children with auditory processing disorders (APD) by incorporating response time measures. A group of children identified in a clinical setting as having APD was compared to an age-matched peer group using a vocal reaction time (VRT) format. The participants were between the ages of 5.5 and 15 years. All children were presented spoken monosyllabic words of the clinical Hebrew speech discrimination test. Statistically significant differences were found, with means in the APD children reflecting slower performance than that of their peers. The two groups did not differ in their performance accuracy. These data show that combining response time measures with percent correct scores improved test sensitivity. Such an approach may hold promise for future clinical applications in the assessment of APD.

Adolescent↗
PubMed1979

Trialwise tracking method for measuring drug-affected sensory threshold changes in animals.

Rats and rhesus monkeys were trained under a multiple schedule, the components of which were random ratio schedules for food presentation and for shock presentation. The discriminative stimulus for the shock presentation component was a pure tone for the rats and a light for the rhesus monkeys. In the test session under the extinction condition for the shock presentation component, the intensity of the discriminative stimulus was successively either decreased by fixed units when the conditioned suppression was observed or increased when the conditioned suppression was not observed. The levels finally oscillated within a narrow range around the threshold. The auditory thresholds of rats were increased by intramuscular administration of quinidine at 20 mg/kg and also by repeated intramuscular administration of kanamycin at 250 and 500 mg/kg/day. In rhesus monkeys, visual thresholds were raised by application of pilocarpine at 0.02-0.16 mg/kg to the eyes and also by subcutaneous administration of LSD-25 at 4-8 micrograms/kg in one monkey and at 20-30 micrograms/kg in another. The method used for tracking the animals' sensory thresholds was sensitive enough to test the selective effect of the drugs and was also a relatively easy way to obtain a stable behavioral baseline for experimental purposes.

Animals↗
PubMed2004

Auditory lexical decision, categorical perception, and FM direction discrimination differentially engage left and right auditory cortex.

Recent neuroimaging and neuropsychological data suggest that speech perception is supported in bilaterally auditory areas. We evaluate this issue building on well-known behavioral effects. While undergoing positron emission tomography (PET), subjects performed standard auditory tasks: direction discrimination of frequency-modulated (FM) tones, categorical perception (CP) of consonant-vowel (CV) syllables, and word/non-word judgments (lexical decision, LD). Compared to rest, the three conditions led to bilateral activation of the auditory cortices. However, lateralization patterns differed as a function of stimulus type: the LD task generated stronger responses in the left, the FM task a stronger response in the right hemisphere. Contrasts between either words or syllables versus FM were associated with significantly greater activity bilaterally in superior temporal gyrus (STG) ventro-lateral to Heschl's gyrus. These activations extended into the superior temporal sulcus (STS) and the middle temporal gyrus (MTG) and were greater in the left. The same areas were more active in the LD than the CP task. In contrast, the FM task was associated with significantly greater activity in the right lateral-posterior STG and lateral MTG. The findings argue for a view in which speech perception is mediated bilaterally in the auditory cortices and that the well-documented lateralization is likely associated with processes subsequent to the auditory analysis of speech.

Acoustic Stimulation↗
PubMed1985

Auditory laterality in depression: relation to circadian patterns and EEG sleep.

Unmedicated endogenous (ED) and nonendogenous depressed (ND) patients were tested in the morning and evening on a dichotic click detection task and a dichotic consonant-vowel (CV) discrimination task. The ED and ND groups showed a morning to evening shift in lateral asymmetry for detecting dichotic clicks, which was opposite in direction to that previously seen for normal subjects. In contrast, there was no morning to evening shift in asymmetry for dichotic CV discrimination. Lateral asymmetry for dichotic click detection was significantly correlated with EEG sleep characteristics (sleep latency, REM period latency, REM time) and ratings of diurnal variation on the Hamilton Depression Scale. A reversal of the normal lateral asymmetry in the morning was associated with lengthened sleep latencies and with clinical ratings of diurnal variation.

Adult↗
PubMed2005

Effects of age and auditory and visual dual tasks on closed-road driving performance.

PURPOSE: This study investigated how driving performance of young and old participants is affected by visual and auditory secondary tasks on a closed driving course. METHODS: Twenty-eight participants comprising two age groups (younger, mean age = 27.3 years; older, mean age = 69.2 years) drove around a 5.1-km closed-road circuit under both single and dual task conditions. Measures of driving performance included detection and identification of road signs, detection and avoidance of large low-contrast road hazards, gap judgment, lane keeping, and time to complete the course. The dual task required participants to verbally report the sums of pairs of single-digit numbers presented through either a computer speaker (auditorily) or a dashboard-mounted monitor (visually) while driving. Participants also completed a vision and cognitive screening battery, including LogMAR visual acuity, Pelli-Robson letter contrast sensitivity, the Trails test, and the Digit Symbol Substitution (DSS) test. RESULTS: Drivers reported significantly fewer signs, hit more road hazards, misjudged more gaps, and increased their time to complete the course under the dual task (visual and auditory) conditions compared with the single task condition. The older participants also reported significantly fewer road signs and drove significantly more slowly than the younger participants, and this was exacerbated for the visual dual task condition. The results of the regression analysis revealed that cognitive aging (measured by the DSS and Trails test) rather than chronologic age was a better predictor of the declines seen in driving performance under dual task conditions. An overall z score was calculated, which took into account both driving and the secondary task (summing) performance under the two dual task conditions. Performance was significantly worse for the auditory dual task compared with the visual dual task, and the older participants performed significantly worse than the young subjects. CONCLUSIONS: These findings demonstrate that multitasking had a significant detrimental impact on driving performance and that cognitive aging was the best predictor of the declines seen in driving performance under dual task conditions. These results have implications for use of mobile phones or in-vehicle navigational devices while driving, especially for older adults.

Adult↗
PubMed1993

Some factors affecting assessment of hearing handicap in the elderly.

In 42 elderly hearing-impaired persons we compared the patient's self-assessment of hearing handicap with the assessment made by the patient's significant other. In general, patients tended to rate themselves as less handicapped than did their significant others. The difference was not affected by degree of loss but was affected by slope of loss and by the presence of central auditory processing deficit. Results support the value of the handicap assessment by the significant other in understanding the communication problems of the elderly patient.

Adult↗
PubMed1990

[Are cochlear outer hair cells the origin of otoacoustic emissions?].

Recent investigations have shown, that cochlear outer hair cells (OHCs) influence actively the micromechanics of the cochlea, beside their capability for auditory perception. A direct evidence for these energy requiring processes has been the registration of otoacoustic emissions in the external ear canal. Motile responses of isolated OHCs following various stimuli have been suggested to be the possible source of the postulated active mechanical processes. These motile events are possibly controlled by the efferent olivocochlear innervation. By means of two monoclonal antibodies, which were directed against external and internal acetylcholine (ACh) receptor epitopes, we were able to visualize ACh-receptors on OHCs. We suspect, that ACh is released into the synaptic cleft and binds to these newly observed receptors. Thereby they may influence the biomechanics of the cochlea.

Acoustics↗