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PubMed1996

A comparative study on the effect of pure-tone exposure of the guinea pig cochlea.

Electrophysiological methods were applied to 160 healthy adult male guinea pigs in order to investigate the effects of pure-tone exposure for 24 h on the inner ear. A reduction in cochlear microphonics (CM), action potential (AP) and endocochlear potential was observed following exposure to 110 dB at 100 Hz, 100 dB at 200 and 600 Hz and 95 dB at 2 kHz. The observed K+ endolymphatic concentration during 40 min anoxia remained unchanged. In contrast K+ decreased in control animals and following exposure to pure tones varying from 110 dB at 60 Hz to 85 dB at 2 kHz. These findings indicate that high frequency tones have a greater effect on inner ear functions than those of lower frequency, decreasing the maximum output voltage of CM and AP but not changing K+ endolymphatic concentration.

Acoustic Stimulation↗
PubMed1996

Detection of frequency modulation in the FM-bat Phyllostomus discolor.

In a two-alternative forced-choice procedure lesser spear-nosed bats, Phyllostomus discolor, had to discriminate between a pure tone stimulus and a sinusoidally frequency-modulated signal generated at the same carrier frequency as the tone. Modulation depths of the SFM stimuli were reduced until the animals' performance dropped below the 75%-correct level which was used to determine difference limens for detection of frequency modulation (FMDL). The dependence of FMDLs on modulation and carrier frequency was systematically investigated. For a carrier frequency of 18.5 kHz, average FMDLs increased from 95 Hz at a modulation frequency of 10 Hz to 820 Hz at a modulation frequency of 2000 Hz which corresponds to Weber ratios (2 delta f/f) of 0.005 and 0.044 respectively. Further, difference limens were found to increase linearly in proportion to carrier frequency throughout a major part (9-74 kHz) of the species' hearing range. In comparison to other mammals, P. discolor has a pronounced capability for frequency discrimination which might be related to the extensive use of individually distinct frequency-modulated communication calls and audio-vocal learning.

Acoustic Stimulation↗
PubMed1985

Differential encoding of rapid changes in sound amplitude by second-order auditory neurons.

Single-cell recordings from the anesthetized gerbil revealed that neurons in the ventral cochlear nucleus, the most peripheral nucleus of the central auditory system, differentially encode a functionally relevant acoustic feature--amplitude modulation. Onset units show the strongest phase--locked responses to amplitude-modulated sounds, followed in order by chopper, primarylike-with-notch and primarylike units. All these neurons show enhanced responses relative to auditory-nerve fibers which provide their ascending inputs. This enhancement occurs over a 90 dB range of sound levels.

Animals↗
PubMed1980

Discharge properties of primary auditory fibres in Caiman crocodilus: comparisons and contrasts to the mammalian auditory nerve.

Single fibre recordings were performed from the auditory nerve of the caiman, Caiman crocodilus. All neurones were spontaneously active (1-80 imp/s). Clicks evoked multiple peaks in the post stimulus time histogram spaced at 1/CF. At high intensities irregularities were observed. The latencies of the first peak observable were intensity-dependent and related to CF. The number of peaks was correlated with tuning properties of the fibre. Frequency threshold curves were asymmetrical, with low frequency slopes less steep than high frequency slopes. Q10 dB was between 1.5 and 7 with best tuning at high CF. CF ranged from 30 Hz to 2.8 kHz, lowest thresholds down to 5 dB SPL. Intensity functions were nonmonotonic. In isointensity contours the best frequency shifted downwards with increasing stimulus level. At highest levels a response dip was observed above CF. Phase locking, two tone suppression and excitability by combination tones were observed. In comparison to the mammalian cochlea similarities and differences were found.

Acoustic Stimulation↗
PubMed1981

Development of responses to acoustic interaural intensity differences in the car inferior colliculus.

Responses of single neurones in the inferior colliculus of anesthetized adult cats and kittens were studied using best-frequency stimuli of varying interaural intensity differences (IID). Two broad classes of neurone, distinguished by the predominant type of input from each ear, were examined. One class of cells received predominantly excitatory input from each er (EE cells). The other class were excited by monaural stimulation of the contralateral ear and showed no response to monaural stimulation of the ipsilateral ear, but inhibition of the excitatory response by simultaneous ipsilateral stimulation (EI cells). Fourteen of the 18 adult EI cells showed marked changes in discharge rate with variation in IID. Adult EI cells showed low response variability and were insensitive to changes in average binaural intensity. In all cases of IID sensitivity, the onset component of the response was less sensitive to IID than the sustained component. Eight out of ten EE cells were insensitive to IID over the range tested. Cells of high best-frequency in kittens younger than 28 days showed irregular changes in discharge rate with variation in IID and wide response variability. Some low-frequency EI cells in young kittens showed sensitivity to IID, but it is unlikely that these could be involved in sound localization as their frequency response was inappropriate. Many cells in kittens aged 31-40 days showed monotonic, adult-like IID functions, but the response variability of these cells remained higher than that of adult cat neurones. These data provide evidence for a developmental change of binaural interaction in the cat.

Aging↗
PubMed1997

Changing-loudness aftereffects: slope of response functions and spectral dependence.

Aftereffects of azimuthal auditory motion may have two components. A sensory component is inferred from strong aftereffects, because they are spectrally dependent and have shallower response functions than those for non-adaptation. Neither property applies to weak aftereffects, suggesting a cognitive component. Two experiments determined whether changing-loudness aftereffects (CLA) might be understood similarly. In a single-interval forced-choice procedure, listeners responded "growing softer" or "growing louder" to test stimuli changing in intensity. In Exp. 1, adapting and test stimuli were diotic and had the same 1-kHz sinusoidal carrier. Although response functions following adaptation were displaced from response functions for non-adaptation-indicating CLA-their slopes were broadly similar. In Exp. 2, stimuli were monotic; adapting frequency was 1 kHz and test frequencies were between 0.5 and 2.0 kHz. CLA was present in most adaptation conditions, but was strongest when the test frequency was 1.0 kHz; functions' slopes again evinced no systematic variation. The two-component hypothesis for CLA is supported by spectral dependence alone. It is argued that the slope of response functions is due to the nulling procedures for measuring auditory aftereffects. The slope depends on whether the adapted property is processed by "direct" and "indirect" mechanisms; aftereffects tap "direct" mechanisms alone, which may affect sensitivity during measurement.

Adult↗
PubMed1995

On the nature and meaning of sinuosity in magnitude-estimation functions.

Magnitude-estimation functions for single observers, derived from multiple judgments of closely spaced stimuli, exhibit a sinuous form in logarithmic coordinates, an observation frequently confirmed since first reported by Luce and Mo (1965). We propose that this can result from reliance on a restricted pool of responses, called "preferred numbers" by Baird and Noma (1975). We describe a model featuring a response band centered on an assumed power function, from which the observer selects from among preferred numbers with equal probability. In simulations, the expected values of these selections oscillate around the underlying power function with an appearance similar to that of Luce-Mo functions. The appearance of these functions depends on values assumed for the scale factor of the power function, the range of intensities considered, and the width of the band from which responses are drawn. We conclude that sinuosity in magnitude-estimation functions does not disconfirm the psychophysical power law.

Arousal↗
PubMed1983

Age-dependent changes of the compound action potential in the guinea pig.

As a measure of age-related changes in the most peripheral neural part of the auditory pathway, the compound action potential of the guinea pig was analyzed. In addition to a marked threshold elevation, there was a significantly lower potential amplitude in old animals. By contrast, the latency of the compound action potential was unchanged. In view of the fact that the relative amplitude increase in the intensity range tested was the same in old as in young animals, the implication is that the auditory-nerve neurons that are still excited do not exhibit functional deterioration with aging.

Aging↗
PubMed1980

Dynamic study of the acoustico-facial reflex by impedance measurement.

Dynamic study of the acoustic reflex has brought into evidence that 1. age has a significant influence on various reflex response parameters 2. study of dynamic parameters of the acoustic reflex enables changes in the reflex arc to be objectified. This is therefore an objective measurement of recruitment in impedance measurement. The author proposes to study the following parameters: rise time, recovery time, and the variations of maximum amplitude as function of sound stimulation intensity. Study of these three parameters provides a highly sensitive test of change in the dynamics of the acoustic reflex, for indeed this test reveals pathology well before the Reflex Decay Test does so.

Acoustic Impedance Tests↗
PubMed1981

The sound intensity-related behaviour of the brain stem response P6 in different forms of hearing disorders.

For clinical purpose it seems appropriate to emphasize especially P6 among the auditory evoked responses (AER). The latency of this positive wave after approximately 6 ms shows a close correlation of the sound intensity: approximately 9.5 ms at the hearing threshold, approximately 5.8 ms at 100 dB CHL (click hearing level). The different forms of hearing disorders always reveal typical latency patterns. Thus, middle ear hearing loss can be distinguished form inner ear hearing loss, and among sensory lesions those of moderate hearing loss exhibit another pattern than those of severe hearing loss. In the same way among neural disorders two types can be separated from each other, probably caused by different ways of genesis. Thus, ERA (electric response audiometry) becomes an objective pendant to the suprathreshold tests and an integrated part of clinical audiometry.

Audiometry↗
PubMed1981

A psychoacoustical study on time resolution of brief intensity changes in dichotic hearing.

Psychoacoustical methods were used to study the phenomena involved in the detected of brief intensity changes within a noise burst. In subjects with normal hearing time intervals between 5 and 100 ms are noticed for the detection depending on the amount of intensity change. The value for a just noticeable difference varies with age and in pathological states. Possible peripheral and central processes of this sort of time resolution ability of the hearing organ are outlined.

Adult↗
PubMed1981

On the overload effect of sound impulses to the inner ear.

Test series with both continuous and intermittent sound exposure to guinea pig ears yielded an area within the coordinates load frequency and load level in which a dose principle is valid more or less exactly. Exceeding the upper (level) borderline of this area provokes a damage of the organ of Corti nearly independent of the load dose. Sound levels of such order of magnitude mainly occur at sound impulses. However, to estimate the hair-cell damaging effect of a given sound impulse one needs its time or frequency function in addition to the peak level. A first order approximation seems to be possible by means of a 1/3-octave band level analysis.

Acoustic Stimulation↗
PubMed1987

Coding of sinusoidally amplitude modulated acoustic stimuli in the inferior colliculus of the rufous horseshoe bat, Rhinolophus rouxi.

Single neuron responses to sinusoidally amplitude modulated (SAM) signals were studied in the inferior colliculus of the horseshoe bat, Rhinolophus rouxi. 57% of the neurons responded to SAM stimuli with periodical discharges synchronized to the modulation cycle. The proportion of cells driven by amplitude modulated signals was independent of the best frequency of the neurons. Best modulation frequencies were at or below 100 Hz in about 70% of the neurons. Synchronized activity could be elicited by modulation frequencies up to 400 Hz. Best SAM responses were observed at stimulus intensities 10 dB above threshold. Generally the BMF of a neuron did not change with intensity. The BMF decreased with decreasing modulation depth of the amplitude modulation. A trend for a topographical organization of neurons according to best modulation frequencies was detected. The results did not reveal any significant specialization of the bat's auditory system for coding of amplitude modulations as compared to other mammals.

Animals↗
PubMed1992

Speech rate, loudness, and cardiovascular reactivity.

This paper reports the results of two studies that investigated the relationship between speech rate, loudness, and cardiovascular reactivity (CVR). One study involved the separate manipulation of speech rate and loudness and assessed its effects on CVR during a routine reading task. The second study involved the simultaneous manipulation of both loudness and speech rate and studied its effects on CVR within the context of a personal interview. In both studies, the reduction of speech rate and/or loudness was associated with a significant reduction in CVR. On the other hand, increasing speech rate and/or loudness had no, or only a very minimal, effect on CVR. It is suggested that in the absence of emotional arousal, especially anger-arousal, rapid and loud speech per se is not associated with significant cardiovascular hyperreactivity. On the other hand, our findings suggest that training people to speak slowly and softly may be an effective approach for the control of cardiovascular hyperreactivity.

Adult↗
PubMed1984

Learned self-control of tinnitus through a matching-to-sample feedback technique: a clinical investigation.

Two cases are reported in which subjective tinnitus aurium was treated with a matching-to-sample procedure. Following baseline evaluations, the subjects' experienced tinnitus was reproduced audiometrically in terms of loudness, frequency, and quality. This was presented to them in the noninvolved ear and was gradually reduced within sessions. The subjects were required to concentrate on reducing their tinnitus until an equal match had been achieved between it and the stimulus sound at each new decibel level. Both subjects gained control over their tinnitus and were able to reduce it markedly from baseline levels. This procedure is viewed as an advance over other techniques not only in that it significantly reduces the tinnitus but in the fact that it is done through the subject's own control, providing psychological benefit as well.

Adult↗