Biomedical subjects

E M Relkin

Publications and source records attributed to E M Relkin.

At least 19 recordsLinked to original sources

PubMed2005

Physiological mechanisms of onset adaptation and contralateral suppression of DPOAEs in the rat.

An investigation was undertaken to measure medial olivocochlear (MOC) reflexes in anesthetized rats before and after sectioning of the middle-ear muscles. Distortion product otoacoustic emission (DPOAE) magnitude and phase temporal responses were measured ipsilaterally to study MOC-mediated "DPOAE onset adaptation" and in the presence of a contralateral noise to study MOC-mediated contralateral "suppression" (terms as used by previous researchers). Distortion product otoacoustic emission onset adaptation and contralateral suppression had predictable changes in direction of magnitude and phase that were dependent on the input-output function. After sectioning of the middle-ear muscles (MEMs), DPOAE onset adaptation and contralateral suppression were greatly reduced, and there were little, if any, changes in phase. These "residual" changes were interpreted as a result of the MOC reflex. The results suggest that what appears to be DPOAE onset adaptation and contralateral suppression can be mediated primarily by MEM reflexes. When studying MOC effects on otoacoustic emissions (OAEs) using acoustic stimulation, it is necessary to make recordings over a span of stimulus levels. In addition, looking at both magnitude and phase of the OAE may help separate what is due to the MOC reflex from MEM reflex.

Acoustic Stimulation↗

PubMed2001

On a psychophysical transformed-rule up and down method converging on a 75% level of correct responses.

Transformed-rule up and down psychophysical methods have gained great popularity, mainly because they combine criterion-free responses with an adaptive procedure allowing rapid determination of an average stimulus threshold at various criterion levels of correct responses. The statistical theory underlying the methods now in routine use is based on sets of consecutive responses with assumed constant probabilities of occurrence. The response rules requiring consecutive responses prevent the possibility of using the most desirable response criterion, that of 75% correct responses. The earliest transformed-rule up and down method, whose rules included nonconsecutive responses, did not contain this limitation but failed to become generally accepted, lacking a published theoretical foundation. Such a foundation is provided in this article and is validated empirically with the help of experiments on human subjects and a computer simulation. In addition to allowing the criterion of 75% correct responses, the method is more efficient than the methods excluding nonconsecutive responses in their rules.

Computer Simulation↗

PubMed1998

Recovery of the human compound action potential following prior stimulation.

The recovery from prior stimulation of the compound action potential (CAP) was measured using a forward masking stimulus paradigm in four normal-hearing, human subjects. The CAP was recorded using a wick electrode placed on the tympanic membrane. The effects of a 4000-Hz, 97-dB SPL conditioning stimulus on CAP amplitude in response to a 4000-Hz probe were measured as a function of conditioner-probe interval for three probe levels. The normalized probe response amplitude was completely recovered to the control values at an average conditioner-probe interval of 1359 ms, similar to that observed in chinchilla (Relkin, E.M., Doucet, J.R., Sterns, A., 1995. Recovery of the compound action potential following prior stimulation: evidence for a slow component that reflects recovery of low spontaneous-rate auditory neurons, Hear. Res. 83, 183-189). The present results are interpreted as a consequence of the slow recovery of low spontaneous-rate (SR), high threshold neurons from prior stimulation (Relkin, E.M., Doucet, J.R., 1991. Recovery from prior stimulation. I: Relationship to spontaneous firing rates of primary auditory neurons. Hear. Res. 55, 215-222) and may provide indirect physiological evidence for the existence of a class of low-SR auditory neurons in humans.

Acoustic Stimulation↗

PubMed1998

A frequency-dependent saturation evident in rate-intensity functions of the chinchilla auditory nerve.

The shape of rate-intensity functions recorded from individual neurons of the auditory nerve using stimulus frequencies at and below the characteristic frequency have been both well-characterized and modeled by other researchers. However, previous studies of rate-intensity functions using stimulus frequencies above the characteristic frequency have primarily focused on the slopes of the rising phases of the functions. Hence, they did not determine whether rate-intensity functions recorded using stimulus frequencies above the characteristic frequency saturate, and, if so, at what firing rates the saturation occurs. In this study, rate-intensity functions have been obtained from neurons of the eighth nerve of the chinchilla in response to gated, sinusoidal stimuli in order to investigate saturation firing rates for frequencies above the characteristic frequency. For each neuron, rate-intensity functions were obtained for stimulus intensities up to 90 dB SPL at the characteristic frequency and at as many frequencies above the characteristic frequency as time would allow. These data clearly reveal that, for frequencies above the characteristic frequency, saturation occurs at a rate that decreases monotonically as the frequency of stimulation is increased. In addition, an empirical equation is given which summarizes the dependence of saturation on stimulus frequency for the data of this study.

Acoustic Stimulation↗

PubMed1997

Neural contributions to the perstimulus compound action potential: implications for measuring the growth of the auditory nerve spike count as a function of stimulus intensity.

The perstimulus compound action potential (PCAP), unlike the more familiar compound action potential (CAP), can be recorded in response to asynchronous as well as synchronous auditory nerve activity. When all neurons contribute equally to the PCAP, the area under the PCAP (the PCAP area) is proportional to the number of action potentials fired by auditory nerve neurons (the auditory nerve spike count). The auditory nerve spike count is one proposed code for stimulus intensity, and our goal is to use the PCAP to test this hypothesis. In this study, two independent tests were developed to measure the contributions of neurons to the PCAP as a function of their characteristic frequency (CF). The test results were verified using a model of the auditory periphery designed to calculate the auditory nerve spike count as a function of pure tone intensity and frequency. In nearly all experiments, neurons having CFs that span contiguous three or four octave bands contribute equally to the PCAP. For pure tones that stimulate only those neurons contributing equally to the PCAP, the PCAP area grows over intensity ranges frequently exceeding 80 dB, and in one case equaling 108 dB. These results demonstrate that the auditory nerve spike count, at least for pure tones, is capable of encoding changes in stimulus intensity over the entire dynamic range of the auditory system.

Animals↗

PubMed1997

Is loudness simply proportional to the auditory nerve spike count?

It is often asserted that the physiological correlate of loudness is the simple sum of the spike activity produced by all neurons in the auditory nerve (the auditory nerve spike count). We will refer to this hypothesis as the spike count hypothesis. The spike count hypothesis has been tested in the past using models of the auditory periphery and in almost all cases, the hypothesis has been supported. Our new technique for recording a compound potential from the chinchilla auditory nerve, the perstimulus compound action potential (PCAP), makes possible the measurement of the growth of the auditory nerve spike count, thus providing data that can be used to test the spike count hypothesis empirically. It was observed that the growth of the auditory nerve spike count in response to a 1-kHz pure tone (in dB/dB) is 33% shallower than the growth of loudness for a 1-kHz tone, and this discrepancy increases to 66% for an 8-kHz tone. In addition, "equal-count" contours were constructed in a manner analogous to equal-loudness contours. It was found that as reference intensity increases, equal-count contours become sharply curved upward at high frequencies whereas equal-loudness contours become increasingly flat. These differences are unlikely to be the result of the cross-species comparison, since the discrepancies are mostly attributable to the skewed pattern of spread of excitation along the basilar membrane, a property shared by humans and chinchillas. Therefore, we conclude that the simple sum of the spike activity in the auditory nerve cannot be the physiological correlate of loudness.

Animals↗

PubMed1995

Recovery of the compound action potential following prior stimulation: evidence for a slow component that reflects recovery of low spontaneous-rate auditory neurons.

Relkin and Doucet (1991) have shown that recovery of single auditory-nerve neurons from the effects of prior stimulation by a 100 ms pure tone varies with the spontaneous activity of the neuron. Recovery of thresholds for low spontaneous-rate (SR) neurons takes up to 2.0 s, a factor of 10 times greater than the 200 ms required for recovery of high SR neurons. The purpose of this study was to see if the different recovery rates for the two classes of neurons is reflected in recovery of the amplitude of the compound and potential (CAP) recorded in response to a brief probe tone with similar prior stimulation. We present evidence for two components in the recovery of the CAP amplitude, a slow and fast component, that have time courses similar to those for the recovery of responses for single low and high SR neurons, respectively. Thus, we conclude that the recovery of the CAP amplitude does indeed reflect the underlying recovery processes of single auditory-nerve neurons.

Acoustic Stimulation↗

PubMed1994

Psychophysical and physiological forward masking studies: probe duration and rise-time effects.

To determine if the amount of forward masking observed in single auditory-nerve fibers of the chinchilla was sufficient to account for the amount of masking observed behaviorally in humans, thresholds for the detection of several types of probe signals following a forward masker were measured in both behavioral and physiological experiments. It is necessary to use the same probe stimulus characteristics in both behavioral and physiological experiments to make valid comparisons between the two measures of forward masking. Experiment 1 was behavioral and used human listeners. Two types of probe signals were used, differing in overall duration and rise/fall times. The two probes yielded different growth of masking functions. These results further demonstrate that forward masking characteristics in behavioral experiments are critically dependent upon the parameters of the probe signal used. Experiment 2 was physiological and used chinchillas. The amount of masking for high-level maskers using the same two probe types in a physiological "forced-choice" experiment are presented. In contrast with the behavioral results, there was little or no difference in the amounts of masking observed for the two probes. In addition, the amounts of masking observed in some auditory-nerve fibers were considerably smaller than those observed behaviorally. These experiments further demonstrate that the amount of forward masking observed in single auditory-nerve fibers is inconsistent with that observed behaviorally.

Acoustic Stimulation↗

PubMed1992

Short-term poststimulatory response characteristics of the human acoustic stapedius reflex: monotic and dichotic stimulation.

Two experiments were performed to study short-term poststimulatory response characteristics of the human acoustic stapedius reflex in the time and intensity domains. In experiment 1, monotic magnitude-intensity functions (MIFs) were obtained for a 20-ms test stimulus preceded by a conditioning stimulus varying in duration (20, 50, 100, 500 ms) and level (-10, 0, +10 dB re: stapedius-reflex threshold) and temporally separated from the test stimulus by various interstimulus intervals (ISIs) (0, 20, 50, 100, 500 ms). Experiment 2 was similar in design except that conditioner and test stimuli were presented dichotically and fewer ISIs were used. Both experiments demonstrated that a prior conditioning stimulus produced significant increases in test-stimulus response magnitude. These poststimulatory effects were characterized by complex interactions among stimulus variables (conditioner duration, conditioner level, and interstimulus interval) with similar interactions occurring for both monotic and dichotic stimuli. A simple superposition effect of the responses to the conditioner and test stimulus does not account for the effect of prior stimulation since responses often exceeded the sum of the responses to the conditioner and the test stimulus alone.

Acoustic Stimulation↗

PubMed1992

Frequency discrimination in forward and backward masking.

Frequency difference limens for pure tones preceded by a forward masker or followed by a backward masker were obtained across a wide range of signal levels. Relkin and Doucet [Hear. Res. 55, 215-222 (1991)] have shown that at a masker-signal delay of 100 ms, the thresholds of high-SR (spontaneous rate) auditory-nerve fibers are recovered, while the low-SR fiber thresholds are not. Therefore, forward-masked frequency discrimination potentially offers a method to investigate the role of low-SR fibers in the coding of frequency. It has been shown that when an intense forward masker is presented 100 ms before a pure-tone signal, intensity difference limens are elevated for mid-level signals [Zeng et al., Hear. Res. 55, 223-230 (1991)]. However, Plack and Viemeister [J. Acoust. Soc. Am. 92, 3097-3101 (1992)] have shown that a similar elevation in the intensity difference limen is obtained under conditions of backward masking, where selective adaptation of the auditory neurons would not be expected to occur. A condition of backward-masked frequency discrimination was therefore included to investigate the role of interference resulting from adding additional stimuli to a discrimination task. For signals at 1000 and 6000 Hz, there was no effect of a forward masker upon frequency difference limens. For the backward-masked conditions, an elevation of the frequency difference limen was observed at all signal levels, demonstrating that the effects of forward and backward maskers upon frequency discrimination are dissimilar and suggesting that cognitive effects are present in backward-masked discrimination tasks.(ABSTRACT TRUNCATED AT 250 WORDS)

Auditory Perception↗

PubMed1991

Recovery from prior stimulation. I: Relationship to spontaneous firing rates of primary auditory neurons.

Recovery of neural thresholds following a forward masker was measured for auditory neurons in anesthetized chinchillas. We find that recovery of forward-masked thresholds is slower for low spontaneous-rate neurons compared to high spontaneous-rate neurons. In addition, we studied the dependence of the shape of PST histograms on the time between repetitions of a tone-burst. We find that for low spontaneous-rate neurons, peak onset responses increase in magnitude over a longer range of interstimulus intervals compared to high spontaneous-rate neurons. Both results are consistent with the conclusion that low spontaneous-rate neurons take longer to recover from prior stimulation compared to high spontaneous-rate neurons. We suggest applications of this finding in psychophysical experiments to investigate the role of low spontaneous-rate neurons in intensity coding.

Acoustic Stimulation↗

PubMed1991

Recovery from prior stimulation. II: Effects upon intensity discrimination.

We obtained just-noticeable differences (jnds) for the intensity of pure tones following a forward masker. The masker was a 100-ms burst of narrow-band noise centered at 1000 Hz presented at 90 dB SPL; the pure-tone signal was at 1000 Hz and was 25 ms in duration. The masker-signal delay was 100 ms. Under these conditions, there is no threshold shift for the detection of the pure-tone signal following the forward masker. In contrast with the absence of a forward-masker effect upon detection thresholds, unusually large midlevel (40-60 dB SPL) jnds were observed. These large midlevel jnds were measured as a function of signal delay, revealing that they are not completely recovered to the normal (unmasked) values by 400 ms. We interpret these data as a consequence of the slower recovery of low-spontaneous rate, high-threshold neurons following prior stimulation (Relkin and Doucet, 1990). These experiments may therefore provide psychophysical evidence that the low-spontaneous rate, high-threshold neurons are a necessary physiological component in the coding of the large dynamic range for intensity. In addition, the present data provide evidence that the assumption that the effect of forward masking is limited to 100-200 ms is inappropriate, as this recovery time does not necessarily apply to suprathreshold tasks.

Acoustic Stimulation↗

PubMed1991

Forward masking of the compound action potential: thresholds for the detection of the N1 peak.

A two-interval forced-choice method was developed that provides a rapid and objective computerized measurement of the threshold for detection of the N1 peak of the compound action potential (CAP) recorded in response to a probe tone. The CAP was recorded at the round window of anesthetized chinchillas and several gerbils. An adaptive threshold-tracking procedure was verified by comparing measured thresholds to those obtained from neurometric functions, which plot the proportion of correct detections of the probe as a function of probe intensity. The adaptive procedure was applied in a forward masking paradigm to study the growth of masking of the CAP as a function of masker intensity. Results indicate that growth of masking of the CAP more closely corresponds to that observed psychophysically, than does forward masking observed in the response of a single neuron. Implications for neural encoding mechanisms are discussed.

Acoustic Stimulation↗

PubMed1991

Threshold and suprathreshold temporal integration effects in the crossed and uncrossed human acoustic stapedius reflex.

Threshold and suprathreshold temporal integration (TI) effects were studied in the crossed and uncrossed human acoustic stapedius reflex. Changes in reflex threshold were compared at four stimulus durations and for six threshold response criteria; suprathreshold effects were similarly compared at four stimulus durations and at five stimulus sound-pressure levels. Our results showed that reflex thresholds were significantly lower for the uncrossed condition and for longer duration stimuli. Both effects were dependent on threshold response criteria. Threshold TI measurements in both crossed and uncrossed conditions were equivalent at low criterion levels (0%-4%, p greater than 0.05) but were significantly larger in the crossed condition at higher criterion levels (5%-6%, p less than 0.05). Prominent suprathreshold effects also occurred. The main effect was characterized by significantly larger reflex magnitudes in the uncrossed condition. Duration dependent slope differences in magnitude intensity functions (MIFs) were also observed and were characterized by steeper slopes for longer duration stimuli. Saturation effects and/or intensity-dependent slope decelerations in MIFs were predominant in the uncrossed condition and for stimulus durations exceeding 20 ms. These data provide further quantitative evidence for asymmetric threshold and suprathreshold response properties of the crossed and uncrossed human acoustic stapedius reflex and demonstrate the dependence of these effects on stimuli of different durations.

Acoustic Stimulation↗

PubMed1989

Forward-masking properties of multicomponent signals in normal and hearing-impaired subjects.

The forward-masking properties of inharmonic complex stimuli were measured both for normal and hearing-impaired subjects. The signal threshold for a 1000-Hz pure-tone probe was obtained for six different maskers, which varied in the number of pure-tone components. The masking stimuli consisted of 1, 3, 5, 7, 9, or 11 components, logarithmically spaced in frequency surrounding the signal and presented at a fixed level of 80 dB SPL per component. In most normal-hearing subjects, the threshold for the probe decreased as the number of masking components was increased, demonstrating that stimuli with more components tended to be less effective maskers. Results from hearing-impaired subjects showed no decrease in threshold with increasing number of masking components. Instead, the thresholds increased as more components were added to the first masker. These results appear to be consistent with suppression effects within the multicomponent maskers for the normal subjects and a lack of suppression effects for the hearing-impaired subjects. The results from the normal-hearing subjects are also consistent with "across-channel" cuing.

Adult↗

PubMed1988

A reexamination of forward masking in the auditory nerve.

Forward masking, as measured behaviorally, is defined as an increase in a signal's detection threshold resulting from a preceding masker. Previously, forward masking in the auditory nerve has been measured as a reduction in the neural response to a signal when preceded by a masker. However, detection threshold depends on both the magnitude of the response to the signal and the variance of the response. Thus changes in detectability cannot be inferred from response reduction alone. Relkin and Pelli (1987) have described a two-interval forced-choice procedure that may be used to measure the threshold for the detection of a probe signal in recordings of spike counts in single auditory neurons. These methods have been used to study the forward masking of characteristic frequency probe tones by characteristic frequency maskers as masker intensity was varied. Although the masker does reduce the detectability of the probe tone, it was found that the threshold shifts are much less than those observed behaviorally, particularly for intense maskers. In part, the small threshold shifts can be attributed to the reduction in response variance following the masker, which is the result of the adaptation of spontaneous activity. These results imply that behavioral forward masking must result from suboptimal processing of spike counts from auditory neurons at a location central to the auditory nerve.

Animals↗

PubMed1987

Antagonistic effects of perilymphatic calcium and magnesium on the activity of single cochlear afferent neurons.

The dependence of the spontaneous and sound driven activity of single cochlear nerve fibers on the calcium and magnesium content of the perilymph was studied by perfusion of the perilymphatic space. It was possible to study these effects under steady-state conditions by continuously perfusing scala tympani at low rates while simultaneously recording from units in the chinchilla auditory nerve. Preparations were stable for many hours. As previously reported [Robertson and Johnstone (1979) Pflügers Arch. 380, 7-12], perfusion with solutions containing elevated concentrations of magnesium reduces both the spontaneous and driven activity. When calcium was eliminated from the perfusate, activity was completely abolished for stimuli with sound pressure levels below 100 dB. During partial blocks, a relatively frequency-independent threshold elevation was seen for frequencies well below the characteristic frequency (CF) of the unit, with greater elevations closer to CF. When the threshold elevation at CF was 30-40 dB, the width of the 'tip' portion of the tuning curve was reduced, resembling that of naturally-occurring units with low spontaneous rates of discharge. These effects are similar to that of raising the criterion for response during threshold measurement and are probably related to a frequency-dependent nonlinearity exhibited by the motion of the basilar membrane. The dynamic range for the growth of average rate with level was increased and saturation was shifted to higher stimulus levels during elevated magnesium perfusion. Raising the calcium content of the perfusate increased both spontaneous and driven rates, even in the saturated portion of the rate-intensity plot. Under these conditions, the response of the unit may more directly correspond to the intracellular potential of the presynaptic hair cell. It is argued that the primary site of divalent cation interaction is in the control of transmitter release. Inner hair cells of the mammalian cochlea apparently do not release transmitter in the absence of a calcium influx. The size of the pool of 'readily-available' transmitter appears to be influenced by divalent cations. Even though this synapse is probably specialized for the transmission of auditory signals, the mechanism of synaptic transmission is probably not fundamentally different from that of other well-characterized synapses.

Animals↗

PubMed1987

Evidence for presynaptic facilitation in primary cochlear afferent neurons.

Evidence for presynaptic facilitation was sought in the discharge patterns of single units in the chinchilla cochlear nerve. Pairs of acoustic clicks, separated by a variable interval, were delivered and spike discharge times stored for offline analysis. By choosing an appropriate binwidth (5 ms) and collecting data only from units with high characteristic frequencies (CF) the response to each click was contained in a single bin. The ratio of spike counts in the bins containing the responses to the two clicks was computed. For units with low spontaneous rates (SR) of discharge (SR less than 8/s), an enhancement of the response to the second click was seen for low stimulus levels. As the stimulus level was raised, the response to the second click became reduced, presumably because of adaptation to the first click. Units with high (SR greater than 15 spikes/s) seldom exhibited enhancement of the response to the second click. The results are explained with a conceptual model in which two processes, depletion and facilitation decay exponentially following a stimulus. Since the two processes have opposite influences on the rate of transmitter release, the magnitudes of both processes may be underestimated by observing their net effect.

Acoustic Stimulation↗