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A L Rupert

Publications and source records attributed to A L Rupert.

At least 19 recordsLinked to original sources
PubMed1997

Interaural time effects on the frequency-following response.

Frequency-following responses (FFRs) were recorded to evaluate differences between monaural and binaural waveforms and waveforms evoked by stimuli with interaural time disparities. Eight normal-hearing adult females served as subjects. The stimuli were monaural and binaural 450-Hz tonebursts at 65 and 60 dB SL and interaural time differences of 0 and 660 microseconds, respectively. Normalized amplitudes and periodicities of FFR waveforms within and between subjects were compared. The results showed asymmetric FFR to the various stimuli used in this study. Binaural FFR waveforms were greater than monaural but smaller than summed monaural FFRs. Binaural FFR amplitudes evoked by a zero time difference were greater than amplitudes evoked by a 660-microseconds difference. Additionally, tight phase-locked periodicities were evoked in the FFR monaurally and binaurally. The averaged FFR periodicity to all stimulus conditions from all subjects was 2.29 msec, differing only 6.8 microseconds from the period of the 450-Hz stimulus. In contrast, monaural and binaural neurons in the lower brain stem typically exhibit much less synchroneities to low-frequency tones than the FFR. These data provide evidence that the FFR is not simply a sum of neuronal action potentials. The findings suggest instead the presence of brainstem neuronal networks. Such putative neuronal ensembles apparently maintain a closer correspondence to the period of a low-frequency sound, whether monaural or binaural, than the discharge patterns of single neurons.

Adult↗
PubMed1996

Inferior colliculus neuronal responses to masking-level-difference stimuli.

Seventy-one inferior colliculus neurons, with best frequencies below 1.5 kHz, were studied in a binaural, forward-masking paradigm in chinchilla. Masker and signal frequencies were presented at neuronal best frequency. Masker level was set 10-15 dB above neuronal threshold and varied to include a range of signal-to-masker ratios and overall intensities. Without the masker, 33 of the neurons preferred an in-phase signal (SO), 29 an out-of-phase (S pi) signal, and the remaining 9 had 'no-preference' (NP), responding equally well to SO and S pi. Complete protocols from 53 of the 71 neurons were obtained with and without maskers over a range of levels. With an in-phase masker (NO), some neurons responded better to dichotic (NOS pi) than to diotic (NOSO) sounds. Generally, they maintained a particular phase preference with and without masker. Some neurons, however, altered phase preference and responsivity when binaural maskers were added to signal. Signal-to-noise ratios between 0 and 30 dB were sufficient to differentiate neuronal responsiveness to NOSO and NOS pi. The results suggest that identical neural mechanisms are not involved in processing unmasked (SO or S pi) and masked binaural sounds (NOSO, NOS pi). Furthermore, changes in neuronal sensitivity favor the NOS pi condition upon addition of noise (NO) to the signal (SO or S pi). We conclude that greater neural activity is generated with stimuli which produce masking-level difference than stimuli that do not.

Acoustic Stimulation↗
PubMed1995

Vowel and vowel sequence processing by cochlear nucleus neurons.

This study examined neuronal discharge rates and temporal patterns to vowels and vowel sequences in chinchilla. The properties of primary-like, chopper, and onset neurons were studied using vowels /i/, /a/, and /u/ individually and paired with separations (0-100 ms), at sound levels above and below thresholds. The interspike interval, period, and post-stimulus-time histograms of all neuronal types to a vowel were modified when in a sequence. Primary-like and chopper discharges were reduced and enhanced depending on vowel sequence parameters; onset neurons exhibited discharge rate reductions only and not enhancements. In addition to rate changes, novel discharge intervals appeared with vowel pairs. An unexpected finding on choppers was that subthreshold levels of the preceding vowel in a paired sequence enhanced discharges to the succeeding one. Reducing levels of preceding or increasing levels of following vowels evoked changes not predictable from single vowel data. Thus the responses to paired vowels in a sequence are interactive. Patterns of discharges and rate functions to vowel sounds from neurons of the same type varied greatly. The cochlear nuclei harbor anatomically and functionally diverse neurons. Because of this heterogeneity, the neural transformations of vowel segments by all cochlear nucleus neuronal types can not be predicted from sinusoidal data.

Acoustic Stimulation↗
PubMed1987

A developmental study of bone conduction auditory brain stem response in infants.

Two studies, vibrator placement and masking, were performed to evaluate the developmental aspect of bone conduction auditory brain stem response (ABR) in human infants. Subject groups included newborns, 1-yr-olds, and adults. In the vibrator studies, ABRs were obtained from placements of the bone conduction vibrator on the frontal, occipital, and temporal bones. Results showed that temporal placements in neonates and 1-yr-olds produce significantly shorter wave V latencies of ABR than frontal or occipital placements. In adults, differences of wave V latencies from various vibrator placements were comparatively small. In the masking studies, ABRs were acquired from vibrator placements at the temporal bone in the presence of ipsilateral air conducted masking noise from the experimental groups. Results showed that interaural attenuations of bone conduction click stimuli are the largest in neonates, somewhat smaller from 1-yr-olds, and the smallest in adults. The findings of this research strongly suggest that temporal placements for bone conduction ABR should be used, in some instances, when testing infants and 1-yr-olds. The results of this study support the proposition that bone conduction ABR is a feasible and reliable diagnostic tool in testing infants.

Adult↗
PubMed1982

Temporal masking of auditory evoked brainstem responses in human newborns and adults.

Temporal masking effects on brainstem evoked responses (BERs) were studied in normal human newborns and adults. Forward masking prolonged the latencies of the newborn BERs significantly longer than adult BERs. The effect of backward masking on BER latencies for both newborns and adults was small, suggesting that either backward masking effects for these stimuli are mediated by structures rostral to the brainstem or that backward masking does not affect the latency of the BER. Increasing the duration of the forward masker prolonged BER latencies more for newborns than adults. Increasing the intensity of the masker prolonged BER latencies for both newborns and adults, however, there were no significant age-intensity interactions.

Acoustic Stimulation↗
PubMed1978

Evaluation of frequency-following potentials in man: masking and clinical studies.

The frequency-following potential (FFP) can have applicability in the assessment of hearing-impaired subjects only if it can be shown that its generation is initiated by neurons which have low best frequencies (2.0 kHz or lower). This study presents results from five subjects with high frequency hearing losses and three subjects with normal hearing. Using 500 Hz tone bursts in the presence of continuous noise of various configurations, it has attempted to determine how in normal hearing subjects, the amplitude and latency of the FFP may be affected. Recordings of the FFP in the presence of noise and wave forms from hearing imparied subjects provide evidence that the FFP is initiated in the cochlea largely by neurons whose best frequencies are 2.0 kHz or lower. Hearing impaired subjects may exhibit 'deviant' responses to tone bursts. These FFP responses may be related to peculiarities of the hearing loss and provide, therefore, a potential means for assessing the temporal viability of the low frequency channels of the auditory neuraxis.

Auditory Perception↗
PubMed1978

Phase locking in monaural and binaural medullary neurons: implications for binaural phenomena.

The synchrony of neural impulses in response to low-frequency sinusoids is described for auditory medullary neurons. The results are summarized as follows: (1) In general, neural synchrony is found to improve with increases in intensity and frequency of stimulation for both monaural and binaural neurons when measurements are make in absolute time. (2) An analysis of our population of neurons implies that two separate mechanisms are responsible for the decrease in synchrony found in many neurons as compared to primarylike neurons with high-locking ability. The two mechanisms are convergence of mistimed impulses and electrontonic changes which occur in dendrites. (3) An analysis of binaural vector strength data provides an explanation for physiological differences between cyclic and noncyclic vector strengths as a function of interaural time and reveals the effects of mistimed convergence upon neural synchrony.(4) In contrast to the inferior colliculus, where the neurons discharge best with contralateral leads in time, superior olivary neurons exhibited no such preference. Some discharge best to ipsilateral while others to contralateral leads. This comparison reveals a striking difference in the coding characteristics of medullary and inferior colliculus neurons. (5) Finally, the results are compared with the psychophysically determined difference limens.

Action Potentials↗
PubMed1975

Human frequency-following responses to monaural and binaural stimuli.

Frequency-following responses, with latencies circa 6 msec, were recorded from five normal-hearing human subjects to brief 500 c/sec tone bursts presented monaurally. The frequency-following responses appear as peaks occurring at 2 msec intervals superimposed on a slow wave (pedestal-like) component. Comparisons were made between the frequency-following responses evoked by binaural and monaural stimuli. The results show that the binaural responses may be interpreted as the sum of two monaural responses. It is concluded, therefore, that there are two independent populations of neurons, each capable of generating a frequency-following response is not a microphonic-like response but rather that the individual waves in the frequency-following response are evoked by the collective activity of phase-locked single units. Finally, on the basis of the distinctness of the individual waves in the frequency-following response, it is concluded that the neural generators of the response must be spatially compact.

Acoustic Stimulation↗
PubMed1975

Functional characteristics of superior olivary neurons to binaural stimuli.

This investigation was undertaken to study the timing properties of low-frequency binaural neurons located in the medulla of kangaroo rat (Dipodomys spectabilis). The results show that the response variables, vector strength (VS) and discharge rate (DR), are not necessarily related responses; each may be conveying a different parameter of acoustic stimuli. The results also lead to the conclusion that binaural low-frequency neurons, whether they are excitatory-excitatory (EE) or excitatory-inhibitory (EI), in essence, function similarly. Finally, this investigation presents findings which suggest that a clock, which may be part of a mechanism for pitch as well as for spatial localization, is activated by sounds, providing thereby a reference signal for neural discharges.

Animals↗