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PubMed1983

Auditory brainstem anomalies in albino cats. I. Evoked potential studies.

The amount of melanin pigmentation in the inner ear is positively correlated with the general pigmentation of the body and specifically with the amount of pigment in the eye. The misrouting of retinofugal projections which accompanies ocular and oculocutaneous albinism has been thought to be a defect in decussation unique to the visual system. Evidence suggests that functional abnormalities may also exist in the auditory systems of albino humans and animals. To evaluate this possibility, evoked potential techniques were used to examine the functional anatomy of decussating brainstem auditory pathways in albino and pigmented cats. Auditory brainstem responses (ABRs) were recorded from albino, pigmented, and Siamese cats using monaural stimulation. ABRs were recorded ipsilateral and contralateral to the stimulated ear. The albinos were complete tyrosinase-negative (cc), not the dominant white (W) variety associated with deafness. In pigmented cats, the amplitudes of ABRs recorded with the reference electrode ipsilateral to the stimulated ear and the ABRs recorded using the reference contralateral to the stimulated ear did not differ by more than 40% for individual components appearing between 2 and 4 ms after stimulus onset. In albino cats the components at these latencies were obliterated or greatly attenuated in the ABR recorded using the reference contralateral to the stimulated ear. These data indicate that anomalies may exist in the brainstem at the level of the acoustic striae, superior olivary nuclei and/or trapezoid body in tyrosinase-negative albino cats.

Animals↗
PubMed1981

Age-related changes in the C57BL/6J mouse cochlea. I. Physiological findings.

The development and degeneration of cochlear output was studied in C57BL/6J mice from the time of hearing onset (12 days of age) through adulthood (50 days of age) using the eighth nerve compound action potential (N1). Mice were stimulated in free-field, using short rise-time tone bursts (2-35 kHz). Sensitivity to tones and threshold tuning curve sharpness (Q10) increased markedly between 12 and 20 days of age. Response latencies changed, in a complex way, to attain minimum values by 20 days of age. The form of intensity function was essentially identical in 12- and 16-day-old mice. In 30- and 40-day-old mice signs of both hearing development and degeneration were seen. For example, while N1 threshold intensities to low-frequency tones continued to decline, those to high frequencies began to increase. The results indicate that some of the previously observed age-related changes in central auditory function in C57BL/6J mice can be accounted for in terms of cochlear evolution. The observed changed in cochlear function are discussed in relation to outer-, middle-, and inner-ear modifications. A basis for the limits of the critical period for audiogenic seizure "priming' is hypothesized.

Aging↗
PubMed1985

Ontogeny of neural discharge patterns in the ventral cochlear nucleus of the mongolian gerbil.

Discharge patterns were recorded extracellularly from single neurons in the ventral cochlear nucleus (VCN) of Mongolian gerbils ranging in age from 10 days after birth (DAB) to adult, a period which includes the onset of responsiveness to acoustic stimulation. At 10 DAB none of the neurons encountered within the VCN responded to acoustic stimulation. At 12 DAB approximately 15% of the neurons isolated in VCN were responsive. This coincided with the earliest cochlear microphonic potentials and preceded the appearance of the cochlear compound action potential (AP) by two days. At 14 DAB, or older, the great majority of neurons isolated in VCN responded to acoustic stimulation. Most parameters of VCN neural function exhibited significant changes between 12 and 18 DAB: neural thresholds improved approximately 100 dB; mean spontaneous discharge rate increased; the high-frequency range of characteristic frequency (CF) values increased from 10.0 to 24.0 kHz; the upper limit for phase locking increased from 0.8 kHz to 3.0 kHz; dynamic range increased from 16 dB to 44 dB, and the proportion of units with well-defined initial onset peaks in their post-stimulus-time (PST) response patterns increased from 40% to 100% of units. Most of the neural parameters examined achieved adult characteristics by 18 DAB. Frequency tuning (Q10dB) matured earlier for high-CF units. The most sharply tuned neurons with high CFs (greater than 4 kHz) at 12 DAB had Q10dB values equal to those for adults. None of the neurons with low CFs (less than 4 kHz) had Q10dB values greater than 1.2 at this age. Classical 'on' PST response patterns were not seen at 12 and 14 DAB. A unique PST response type, characterized by very long latency phasic discharge, was observed only at 12 DAB. None of the VCN neurons recorded from 12 DAB subjects displayed rhythmic 'bursting' or 'pulsing' PST response patterns, as has been reported at the earliest stages of functional development in the VCN of the cat. Most units were capable of sustained discharge, even with long stimulus durations. Units with 'primary-like' PST response patterns at 12 exhibited greater variability in first spike latency and less pronounced initial rates of firing than was characteristic in adults, resulting in poorly defined onset peaks. In contrast, units with chopper PST response patterns showed well-defined onset peaks.

Animals↗
PubMed1995

Information processing during cardiac surgery: an event related potential study.

The aim of this study was to investigate whether information processing persists during general anesthesia, and if so, to determine the relationship between the degree of cognitive processing measured during anesthesia and the presence or absence of intraoperative memories measured after anesthesia. Subjects were 12 patients, undergoing cardiac surgery with propofol/alfentanil anesthesia. During several periods of the operation, event related potentials (ERPs) to frequent and infrequent tones of different pitch were analyzed. After the operation, a word recognition task with ERP recording was administered to determine whether intraoperatively presented words would elicit a (covert) recognition reaction in the brain. ERP wave forms could be obtained during the intraoperative recording periods but differed substantially from those in the awake state. The presence of ERP components up to 500 msec after stimulus presentation suggests that auditory information processing continued during anesthesia up to a certain level of cognition. Intraoperative ERPs to frequent and infrequent tones were not different from each other implying that differences in pitch could not be detected. The postoperative results demonstrated evidence for intraoperative memories in 3 patients. For 2 of these 3 patients, low propofol levels as well as reliable ERPs with large amplitudes were found close to the moment of information presentation. The results emphasize the importance of combining intra- and postoperative measurements and suggest that late ERP components might be used as indicators of an increased risk of auditory perception.

Acoustic Stimulation↗
PubMed2003

Gap detection in Mongolian gerbils (Meriones unguiculatus).

Hearing thresholds for white-noise stimuli and temporal gap-detection thresholds in six Mongolian gerbils (Meriones unguiculatus) were determined in a GO/NOGO procedure using the method of constant stimuli. Gerbils were offspring of animals collected in the field and only bred in captivity for four generations or less. Hearing thresholds for 800 ms bursts of white noise ranged between -0.8 and 6.3 dB SPL. The median minimum-detectable gap centered in an 800 ms burst of white noise presented at 50 dB SPL was 2.1 ms. At levels of 40 dB SPL and above, gap-detection thresholds were independent of the sound-pressure level of the stimulus. At 30 dB SPL and below, the minimum-detectable gap increased with decreasing sound-pressure level. Near 5 dB sensation level, gap-detection thresholds ranged from 13.6 to 29.4 ms. The median threshold for the detection of gaps inserted 5 ms after the onset of an 800 ms burst of white noise of 50 dB SPL was 2.3 ms. The individuals' detection thresholds varied between 2.3 and 3.6 ms for stimuli in which the relative sound-pressure levels of the noise before and after the gap differed by up to 20 dB. The data found in the Mongolian gerbil match results from other mammal and bird species.

Acoustic Stimulation↗
PubMed2000

Asymmetrical olfactory acuity and neuroleptic treatment in schizophrenia.

Uni-rhinal olfactory acuity in schizophrenia was investigated in two experiments. The first assessed the presence of a predicted atypical asymmetry of nostril laterality and the second assessed the effect of antipsychotic treatment on the asymmetry. Although olfactory identification impairment has been well documented in schizophrenia, olfactory acuity has been neglected. This may be an oversight as cerebral structures of the mesial temporal lobe important to olfactory perception have often been implicated in the pathophysiology of schizophrenia and it is thus reasonable to postulate a primary impairment of olfactory acuity in schizophrenia. In addition, unmedicated patients with schizophrenia have exhibited asymmetrical laterality favouring the right over the left hemisphere in studies of visual, haptic, and auditory perception, and the few published prospective treatment studies have suggested a reversal of this asymmetry with first generation neuroleptic treatments. In experiment 1 a generalization of the perceptual asymmetry to olfactory acuity was examined by measurement of n-butanol olfactory thresholds with the Connecticut Chemosensory Perception Exam (CCPE) in an unmedicated sample of 17 patients with schizophrenia and 17 age, gender, and handedness matched normal controls. The patient sample showed an asymmetrical impairment of the left nostril that was not apparent in the normal control sample. In experiment 2, the CCPE was administered to a new sample of 10 patients with schizophrenia before and after neuroleptic treatment. The asymmetry observed in experiment 1 was replicated, and the relative advantage of the right nostril shifted to a relative advantage of the left nostril over the course of 8weeks of treatment. Results are discussed in relation to cerebral aspects of schizophrenia and potential implications to cognitive change from treatment.

Adult↗
PubMed2001

Cross-modal integration of auditory and visual motion signals.

Real-world moving objects are usually defined by correlated information in multiple sensory modalities such as vision and hearing. The aim of our study was to assess whether simultaneous auditory supra-threshold motion introduces a bias or affects the sensitivity in a visual motion detection task. We demonstrate a bias in the perceived direction of visual motion that is consistent with the direction of the auditory motion (audio-visual motion capture). This bias effect is robust and occurs even if the auditory and visual motion signals come from different locations or move at different speeds. We also show that visual motion detection thresholds are higher for consistent auditory motion than for inconsistent motion, provided the stimuli move at the same speed and are co-localised.

Acoustic Stimulation↗
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↗
PubMed2006

Effects of level and frequency on the audibility of partials in inharmonic complex tones.

The effect of level and frequency on the audibility of partials was measured for complex tones with partials uniformly spaced on an equivalent rectangular bandwidth (ERB(N)) number scale. On each trial, subjects heard a sinusoidal "probe" followed by a complex tone. The probe was mistuned downwards or upwards (at random) by 4.5% from the frequency of one randomly selected partial in the complex. The subject indicated whether the probe was higher or lower in frequency than the nearest partial in the complex. The frequencies were roved from trial to trial, keeping frequency ratios fixed. In experiment 1, the level per partial, L, was 40 or 70 dB SPL and the mean frequency of the central partial, f(c), was 1201 Hz. Scores for the highest and lowest partials in the complexes were generally high for all spacings. Scores for the inner partials were close to chance at 0.75-ERB(N) spacing, and improved as the spacing was increased up to 2 ERB(N). For intermediate spacings, performance was better for the lower level used. In experiment 2, L was 70 dB SPL and f(c) was 3544 Hz. Performance worsened markedly for partial frequencies above 3544 Hz, consistent with a role of phase locking.

Acoustic Stimulation↗
PubMed1984

Frequency and intensity difference limens for harmonics within complex tones.

A two-interval, two-alternative forced choice task was used to estimate frequency difference limens (DLs) for individual harmonics within complex tones, and DLs for the periodicity (i.e., number of periods per s) of the whole complexes. For complex tones with equal-amplitude harmonics, the DLs for the lowest harmonics were small (less than one percent). The DLs increased rather abruptly around the fifth to seventh harmonic. The highest harmonic in each complex was also well discriminated, and the discriminability of a single high harmonic was markedly improved by increasing its level relative to the other components. The DL for a complex tone was generally smaller than the frequency DL of its most discriminable component. The DL for a complex was found to be predictable from the DLs of the harmonics comprising the complex, using a formula derived by Goldstein [J. Acoust. Soc. Am. 54, 1496-1516 (1973)] from his optimum processor theory for the formation of the pitch of complex tones. The DL for a complex is sometimes primarily determined by high harmonics, such as the highest harmonic, or a harmonic whose level exceeds that of adjacent harmonics. We also measured intensity DLs for individual harmonics within complex tones. The intensity DLs were smallest for low harmonic numbers, and for the highest harmonic in a complex. An excitation-pattern model was used to determine whether the frequency DLs of harmonics within complex tones could be explained in terms of place mechanisms, i.e., in terms of changes in the amount of excitation at appropriate frequency places. We conclude that place mechanisms are not adequate, and that information about the frequencies of individual harmonics is probably carried in the time patterning of neural impulses.

Auditory Perception↗
PubMed1984

Concurrent minimum audible angle: a re-examination of the concept of auditory spatial acuity.

Minimum audible angle was measured for simultaneous acoustic events. Localization of concurrent events was found to be a direct function of the spectral differences between the events, the angle between the sources, and the location of the sources within the field defined by the subject. In the latter case, the m.a.a. was smallest with sources placed symmetrically about the listener's median plane and maximal at the extreme lateral portions. Post-hoc tests were completed which indicate that the spectral limits for concurrent localization is dependent both upon the angular separation of the sources and the position within the field as defined by the locus of the subject. The functions obtained approach the values reported by Mills [J. Acoust. Soc. Am. 30, 237-246(1958)] as the temporal overlap between the concurrent events decreased. The present results suggest that a single localization function may exist with the optimal performance observed with fully successive stimuli and poorest performance in the condition involving simultaneous events. The implications of these results are discussed.

Auditory Perception↗
PubMed1984

The relations among critical ratios, critical bands, and intensity difference limens in man.

Band-narrowing estimates of the critical bandwidth (CB) are consistently larger than critical-ratio (CR) estimates for the same signal frequency. Bilger [in Hearing and Davis: Essays Honoring Hallowell Davis, edited by S.K. Hirsh et al. (Washington U.P., St. Louis, 1976), p. 191] proposed that this difference could be accounted for by reference to intensity-discrimination performance [CR(Hz)/CB(Hz) = delta I/I]. To test this hypothesis, band-narrowing, critical-ratio, and intensity-discrimination data were collected for four normally hearing, well-trained listeners. Signal frequency was 2000 Hz and two noise levels were used: 20 and 50 dB N0. The relations proposed by Bilger among critical-bandwidth estimates from band-narrowing experiments, critical-ratio estimates from pure-tone detection in wideband noise, and intensity discrimination for a critical-band-wide noise in wideband noise are not supported by the results of individual listeners, or results averaged across listeners.

Adult↗
PubMed1988

Minimum audible movement angle as a function of signal frequency and the velocity of the source.

Thresholds for the detection of the direction of travel of a moving sound source were determined in a single-interval, forced-choice paradigm. Both the rate at which the sound source is displaced (8 degrees-128 degrees/s) and the frequency of the signal to be localized (500-3700 Hz) affect dynamic spatial resolution. There is an inverse relationship between spatial resolution and the rate of travel, a finding that replicates an earlier observation on performance with sources displaced at high velocities [Perrott and Musicant, J. Acoust. Soc. Am. 62, 1463-1466 (1977)]. However, the magnitude of this effect depends on the actual velocities employed. Relatively small changes in spatial resolution are apparent for velocities below approximately 32 degrees/s. The significant frequency effect can be summarized as follows: Dynamic spatial resolution is better for signals below 1000 Hz than for signals above this value (within the range tested). Particularly poor resolution is evident for signals between 1300-2000 Hz. The present results indicate that signal frequency affects dynamic spatial resolution in a fashion similar to that which has been observed in the more common "static" localization test situation. There is no indication of an interaction between these two variables. These results provide additional support for the hypothesis that both static and dynamic spatial discrimination functions are dependent upon the same underlying mechanisms. The effects of velocity upon the spatial resolution problem, a unique aspect of the dynamic paradigm, can probably be explained without the necessity of additional hypothetical mechanisms in the auditory system (e.g., a specialized motion detector).

Adult↗
PubMed1992

The role of frequency selectivity in measures of auditory and vibrotactile temporal resolution.

The purpose of this study was to compare the role of frequency selectivity in measures of auditory and vibrotactile temporal resolution. In the first experiment, temporal modulation transfer functions for a sinusoidally amplitude modulated (SAM) 250-Hz carrier revealed auditory modulation thresholds significantly lower than corresponding vibrotactile modulation thresholds at SAM frequencies greater than or equal to 100 Hz. In the second experiment, auditory and vibrotactile gap detection thresholds were measured by presenting silent gaps bounded by markers of the same or different frequency. The marker frequency F1 = 250 Hz preceded the silent gap and marker frequencies after the silent gap included F2 = 250, 255, 263, 310, and 325 Hz. Auditory gap detection thresholds were lower than corresponding vibrotactile thresholds for F2 markers less than or equal to 263 Hz, but were greater than the corresponding vibrotactile gap detection thresholds for F2 markers greater than or equal to 310 Hz. When the auditory gap detection thresholds were transformed into filter attenuation values, the results were modeled well by a constant-percentage (10%) bandwidth filter centered on F1. The vibrotactile gap detection thresholds, however, were independent of marker frequency separation. In a third experiment, auditory and vibrotactile rate difference limens (RDLs) were measured for a 250-Hz carrier at SAM rates less than or equal to 100 Hz. Auditory RDLs were lower than corresponding vibrotactile RDLs for standard rates greater than 10 Hz. Combination tones may have confounded auditory performance for standard rates of 80 and 100 Hz. The results from these experiments revealed that frequency selectivity influences auditory measures of temporal resolution, but there was no evidence of frequency selectivity affecting vibrotactile temporal resolution.

Adult↗
PubMed1993

Auditory demonstrations on compact disk for large N.

The popular compact disk entitled Auditory Demonstrations, sponsored by the Acoustical Society of America, includes a number of demonstrations that lead to quantitative results. Those demonstrations are evaluated here in the context of a sizeable class in a lecture room. Demonstrations concern masking, loudness, and pitch; specifically they are numbers 2, 3, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 20, and 25. The evaluations find that most of the demonstrations successfully illustrate psychoacoustical principles in a classroom context; others are less successful or require special circumstances for success. Explanations for success and failure are offered, together with some suggestions for optimizing the chances of success.

Acoustic Stimulation↗
PubMed1998

"Central" auditory gap detection: a spatial case.

Normal listeners were tested for their temporal auditory gap detection thresholds using free-field presentation of white-noise stimuli delivered from the left (L) and right (R) poles of the interaural axis. The noise bursts serving as the leading and trailing markers for the silent period were presented in either the same (LL,RR) or different (LR,RL) auditory locations. The duration of the leading marker was a second independent variable. Gap thresholds for stimuli in which the markers had the same location were low, and usually were independent of the duration of the leading marker. Gap thresholds for the LR and RL conditions were longer. These gap thresholds were sensitive to the duration of the leading marker, and increased as the leading marker duration decreased. This finding is consistent with the hypothesis that a relative timing operation mediates gap detection when the markers activate different perceptual channels. The present data suggest that this timing process can operate on perceptual channels emerging from central nervous system processing.

Adult↗
PubMed1999

Amplitude-modulation detection at low- and high-audio frequencies.

Estimates of temporal acuity under comparable conditions at low- and high-audio frequencies are rare. The present study used the amplitude-modulation detection paradigm to estimate temporal acuity over a range of audio frequencies from 800 to 12,800 Hz. Amplitude-modulation detection was measured as a function of modulation frequency for bandlimited noise carriers, and the resulting temporal modulation-transfer functions were used to characterize temporal acuity. The most important result from the two experiments reported is that systematic manipulations of carrier upper-cutoff frequency produced estimates of temporal acuity that did not vary from 800 to 12,800 Hz. When the modulated noise bands were filtered after modulation to control for potential spectral cues, the low-pass cutoff of the modulation-transfer function varied with the carrier bandwidth. However, when the standard stimulus was a quasifrequency-modulated (QFM) noise and the signal was an unfiltered, amplitude-modulated noise, the low-pass cutoff of the modulation-transfer function was independent of carrier bandwidth. These results are consistent with a growing body of evidence demonstrating that auditory temporal acuity is constant throughout most of the audible frequency range.

Adult↗