Andrey Polyakov

Technion - Israel Institute of Technology, H̱efa, Haifa, Israel

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Publications (19)32.84 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: To study effects of forward masking and rapid stimulation on human monaurally- and binaurally-evoked brainstem potentials and suggest their relation to synaptic fatigue and recovery and to neuronal action potential refractoriness. Auditory brainstem evoked potentials (ABEPs) were recorded from 12 normally- and symmetrically hearing adults, in response to each click (50 dB nHL, condensation and rarefaction) in a train of nine, with an inter-click interval of 11 ms, that followed a white noise burst of 100 ms duration (50 dB nHL). Sequences of white noise and click train were repeated at a rate of 2.89 s(-1). The interval between noise and first click in the train was 2, 11, 22, 44, 66 or 88 ms in different runs. ABEPs were averaged (8000 repetitions) using a dwell time of 25 micros/address/channel. The binaural interaction components (BICs) of ABEPs were derived and the single, centrally located equivalent dipoles of ABEP waves I and V and of the BIC major wave were estimated. The latencies of dipoles I and V of ABEP, their inter-dipole interval and the dipole magnitude of component V were significantly affected by the interval between noise and clicks and by the serial position of the click in the train. The latency and dipole magnitude of the major BIC component were significantly affected by the interval between noise and clicks. Interval from noise and the click's serial position in the train interacted to affect dipole V latency, dipole V magnitude, BIC latencies and the V-I inter-dipole latency difference. Most of the effects were fully apparent by the first few clicks in the train, and the trend (increase or decrease) was affected by the interval between noise and clicks. The changes in latency and magnitude of ABEP and BIC components with advancing position in the click train and the interactions of click position in the train with the intervals from noise indicate an interaction of fatigue and recovery, compatible with synaptic depletion and replenishing, respectively. With the 2 ms interval between noise and the first click in the train, neuronal action potential refractoriness may also be involved.
    Hearing Research 08/2004; 193(1-2):83-94. DOI:10.1016/j.heares.2004.03.004 · 2.85 Impact Factor
  • Andrey Polyakov, Hillel Pratt
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    ABSTRACT: To study, in humans, the effects of sound source azimuth and elevation on primary auditory cortex binaural activity associated with sound localization. Middle Latency Auditory Evoked Potentials (MLAEPs) were recorded from three channels, in response to alternating polarity clicks, presented at a rate of 5/sec, at nine virtual spatial locations with different azimuths and elevations. Equivalent dipoles of Binaural Interaction Components (BICs) of MLAEPs were derived from 15 normally and symmetrically hearing adults by subtracting the response to binaural clicks at each spatial location from the algebraic sum of responses to stimulation of each ear alone. The amplified potentials were averaged over 4000 repetitions using a dwell time of 78 micro sec/address/channel. Variations in magnitudes, latencies and orientations of the dipole equivalents of cortical activity were noted in response to the nine spatial locations. Middle-latency BICs included six major components corresponding in latency to the vertex-neck recorded components of MLAEP. A significant decrease of equivalent dipole magnitude was observed for two of the components: Pa2 in response to clicks in the backward positions (medium and no elevation); and Nb in response to clicks in the back and front positions (medium and no elevation) in the midsagittal plane. In the coronal plane, Pa2 equivalent dipole magnitude significantly decreased in response to right-horizontal (no elevation) clicks. Significant effects on equivalent dipole latencies of Pa2 were found for backward positions (no elevation) in the midsagittal plane. No significant effects on Pa2 and Nb equivalent dipole orientations were found across stimulus conditions. The changes in equivalent dipole magnitudes and latencies of MLAEP BICs across stimulus conditions may reflect spectral tuning in binaural primary auditory cortex neurons processing the frequency cues for sound localization.
    Ear and Hearing 05/2003; 24(2):143-55. DOI:10.1097/01.AUD.0000058109.44006.47 · 2.83 Impact Factor
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    Andrey Polyakov, Hillel Pratt
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    ABSTRACT: Our objective was to study the effects of sound source direction and elevation on human brainstem electrical activity associated with sound localization. The subjects comprised 15 normal-hearing and symmetrically hearing adults Auditory brainstem evoked potentials (ABEPs) were recorded from three channels, in response to alternating-polarity clicks, presented at a rate of 21.1/s, at nine virtual spatial locations with different direction and elevation attributes Equivalent dipoles of the binaural interaction components (BICs) of ABEPs were derived by subtracting the response to binaural clicks at each spatial location from the algebraic sum of monaural responses to stimulation of each ear in turn. The BICs included two major components corresponding in latency to the vertex-neck-recorded components V and VI of ABEP. A significant decrease of the first BIC's equivalent dipole magnitude was observed for clicks in the horizontal-frontal position (no elevation) in the midsagittal plane, and for clicks in the left-horizontal (no elevation) and right diagonally above the head (medium elevation) positions in the coronal plane, compared to clicks positioned directly above the head. Significant effects on equivalent dipole latencies of this component were found for front-back positions in the midsagittal plane and left-right positions in the coronal plane, compared to clicks positioned directly above the head. The most remarkable finding was a significant change in equivalent dipole orientations across stimulus conditions. We conclude that the changes in BIC equivalent dipole latency, amplitude and orientation across stimulus conditions reflect differences in the distribution of binaural pontine activity evoked by sounds in different spatial locations.
    International Journal of Audiology 05/2003; 42(3):140-51. · 1.43 Impact Factor
  • Andrey Polyakov, Hillel Pratt
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    ABSTRACT: The objective of the present study was to compare the effects of high stimulus rate and click position in the train on monaurally and binaurally evoked activities in the human auditory brainstem and suggest their possible physiological mechanism. Auditory brainstem evoked potentials (ABEPs) were recorded from 15 normally and symmetrically hearing adults from 3 channels, in response to 50dB nHL, alternating polarity clicks, presented at a rate of 21/s as well as separately to each click in a train of 10 with an interstimulus interval of 11ms. Click trains were presented at a rate of 5.13/s. The binaural interaction components (BICs) of ABEPs were derived by subtracting the response to binaural clicks from the algebraic sum of monaural responses. Single, centrally located equivalent dipoles were estimated as concise measures of the surface-summated activity of ABEPs and BICs generators. A significant effect of click position in the train on equivalent dipole latency of ABEP component V and on equivalent dipole magnitude of III were found. Latency was prolonged and amplitude was increased the later the click's position in the train. A significant effect of click position in the train on equivalent dipole latencies of all components of BICs was found. Latencies were prolonged if the click's position occurred later in the train, with most of the latency shift achieved by the third click in the train for the first major BIC and by the seventh click for other BIC components. No significant effects on equivalent dipole magnitudes of BICs were found. No significant effect of click position in the train on orientation of any of the equivalent dipoles of ABEP or BIC was found. The progressive prolongation of latency of ABEP and BIC components with advancing position in the train may be attributed to cumulatively decreased synaptic efficacy at high stimulus rates, resulting in prolonged synaptic delays along the auditory pathway. The paradoxic enhancement of ABEP dipole III magnitude with advancing click position in the train may reflect higher sensitivity of inhibitory brainstem neurons to increased stimulus rate, resulting in disinhibition. The absence of significant effects on BIC dipole magnitudes may reflect the amplifying effect of divergence in the ascending auditory pathway, as has been observed for the monaurally evoked ABEP components from the upper pons.
    Clinical Neurophysiology 03/2003; 114(2):366-75. DOI:10.1016/S1388-2457(02)00372-3 · 2.98 Impact Factor
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    ABSTRACT: Subjects with brainstem lesions due to either an infarct or multiple sclerosis (MS) underwent two types of binaural testing (lateralization testing and interaural discrimination) for three types of sounds (clicks and high and low frequency narrow-band noise) with two kinds of interaural differences (level and time). Two major types of abnormalities were revealed in the lateralization performances: perception of all stimuli, regardless of interaural differences (time and/or level) in the center of the head (center-oriented), or lateralization of all stimuli to one side or the other of the head (side-oriented). Similar patterns of abnormal lateralization (center-oriented and side-oriented) occurred for MS and stroke patients. A subject's pattern of abnormal lateralization testing was the same regardless of the type of stimulus or type of interaural disparity. Lateralization testing was a more sensitive test than interaural discrimination testing for both types of subjects. Magnetic resonance image (MRI) scanning in three orthogonal planes of the brainstem was used to detect lesions. A semi-automated algorithm superimposed the auditory pathway onto each MRI section. Whenever a lesion overlapped the auditory pathway, some binaural performance was abnormal and vice versa. Given a lateralization test abnormality, whether the pattern was center-oriented or side-oriented was mainly determined by lesion site. Center-oriented performance was principally associated with caudal pontine lesions and side-oriented performance with lesions rostral to the superior olivary complex. For lesions restricted to the lateral lemniscus and/or inferior colliculus, whether unilateral or bilateral, just noticeable differences (JNDs) were nearly always abnormal, but for caudal pontine lesions JNDs could be normal or abnormal. MS subjects were more sensitive to interaural time delays than interaural level differences particularly for caudal pontine lesions, while stroke patients showed no differential sensitivity to the two kinds of interaural differences. These results suggest that neural processing of binaural stimuli is multilevel and begins with independent interaural time and level analyzers in the caudal pons.
    Hearing Research 06/2000; 143(1-2):29-42. DOI:10.1016/S0378-5955(00)00019-8 · 2.85 Impact Factor
  • H Pratt, A Polyakov
    Electroencephalography and clinical neurophysiology. Supplement 02/1999; 50:235-42. DOI:10.1016/S0013-4694(97)88026-5
  • Andrey Polyakov, Hillel Pratt, Yongbing Shi
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    ABSTRACT: Auditory brain-stem evoked potentials (ABEPs) were recorded from 10 normal hearing subjects in response to rarefaction clicks, presented at a rate of 11/s. Stimuli were binaurally symmetrical and isochronic at 75 dB peSPL or with interaural time disparities (ITDs) of +/-0.4 ms, or intensity disparities (IIDs) of +/-10 dB. Potentials were recorded from vertex-neck, as well as from 3 orthonormally positioned differential derivations. The amplified potentials were averaged over 8000 repetitions using a dwell time of 20 micros/address/channel. The effects of contralateral stimulation on neural responses of the peripheral auditory system were obtained by subtracting the binaural response from the algebraic sum of responses to left and right monaural stimuli. From the 3 orthonormal derivations, 3-channel Lissajous' trajectories (3-CLTs) to the various stimulus conditions and difference waveforms were derived. The results corroborated earlier studies on binaural interaction components (BICs), which include 3 major components corresponding in latency to the vertex-mastoid peaks IV-VI of ABEP. In addition, the binaural difference waveforms included 3 earlier, low-amplitude components. Latency correspondence and comparison of difference waveform and ABEP 3-CLTs indicated that the first and third early difference waveform components corresponded to the negative peaks following I and III, respectively, of the vertex-neck ABEP to binaural clicks. These results indicate that early ABEP peaks, generated peripheral to binaural convergence, may be affected by contralateral stimulation. These contralateral effects were in a pattern compatible with suppression. most probably by efferents of the olivo-cochlear bundle.
    Electroencephalography and Clinical Neurophysiology 12/1998; 108(6):543-53. DOI:10.1016/S0168-5597(98)00034-3
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    ABSTRACT: Four sets of measurements were obtained from 11 patients (44-80 years old) with small, localized pontine lesions due to vascular disease: (1) Monaural auditory brain-stem evoked potentials (ABEPs; peaks I to VI); (2) Binaural ABEPs processed for their binaural interaction components (BICs) in the latency range of peaks IV to VI; (3) magnetic resonance imaging (MRI) of the brain-stem; and (4) psychoacoustics of interaural time disparity measures of binaural localization. ABEPs and BICs were analyzed for peak latencies and interpeak latency differences. Three-channel Lissajous' trajectories (3-CLTs) were derived for ABEPs and BICs and the latencies and orientations of the equivalent dipoles of ABEP and BICs were inferred from them. Intercomponent latency measures of monaurally evoked ABEPs were abnormal in only 3 of the 11 patients. Consistent correlations between sites of lesion and neurophysiological abnormality were obtained in 9 of the 11 patients using 3-CLT measures of BICs. Six of the 11 patients had absence of one or more BIC components. Seven of the 11 had BICs orientation abnormality and 3 had latency abnormalities. Trapezoid body (TB) lesions (6 patients) were associated with an absent (two patients with ventral-caudal lesions) or abnormal (one patient with ventral-rostral lesions) dipole orientation of the first component (at the time of ABEPs IV), and sparing of this component with midline ventral TB lesions (two patients). A deviant orientation of the second BICs component (at the time of ABEPs V) was observed with ventral TB lesions. Psychoacoustic lateralization in these patients was biased toward the center. Rostral lateral lemniscus (LL) lesions (3 patients) were associated with absent (one patient) or abnormal (two patients) orientation of the third BICs component (at the time of ABEPs VI); and a side-biased lateralization with behavioral testing. These results indicate that: (1) the BICs component occurring at the time of ABEPs peak IV is dependent on ventral-caudal TB integrity; (2) the ventral TB contributes to the BICs component at the time of ABEPs peak V; and (3) the rostral LL is a contributing generator of the BICs component occurring at the time of ABEP peak VI.
    Electroencephalography and Clinical Neurophysiology 10/1998; 108(5):511-20. DOI:10.1016/S0168-5597(98)00029-X
  • Andrey Polyakov, Hillel Pratt
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    ABSTRACT: The purpose of this study was to compare the effects of monaural and binaural broadband masking noise on binaural interaction components (BICs) of the human auditory brain stem evoked potentials (ABEPs). The BICs of the human ABEPs were studied by subtracting the potentials to binaural clicks from the algebraic sum of monaurally evoked potentials to clicks alone or to clicks with ipsilateral monaural or binaural broadband masking noise. Alternating polarity, 11/sec clicks were presented at 65 dB nHL, and noise was presented at 45 dB nHL. Analysis included peak-to-prestimulus baseline amplitudes and latencies of BICs' peaks and troughs from the vertex-mastoid (A) and vertex-neck (Z) channels. In addition, 3-channel Lissajous' trajectory (3-CLT) analysis, estimating the single, centrally located dipole equivalent of surface activity, was performed on data recorded from three orthogonally positioned electrode pairs. 3-CLT measures included apex latency, amplitude, and orientation, as well as planar segment duration, size, shape, and orientation. All BICs 3-CLTs included five main components (labeled BdI, BdII, BdIII, BeI, and BeII). In general, apex latencies were longer with masking noise. However, BdII and BeI apex latencies were shorter with binaural than with ipsilateral monaural masking noise. Apex amplitude and planar segment size of component BeI, as well as P1 peak amplitude in BICs of the Z-channel records, were larger with binaural than with monaural noise. No significant difference between the monaural and binaural noise conditions was found in durations, shapes, and orientations of planar segments of BICs 3-CLT, nor in peak latency of BICs in the A- and Z-channel records. We suggest that these effects on the latency and amplitude of BICs reflect binaural processing in the human brain stem. In particular, the larger amplitudes and shorter latencies of P1 and BeI with binaural than with ipsilateral monaural masking may be associated with the psychophysical effect of binaural masking level difference.
    Ear and Hearing 07/1998; 19(3):232-9. DOI:10.1097/00003446-199806000-00006 · 2.83 Impact Factor
  • Hillel Pratt, Yongbing Shi, Andrey Polyakov
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    ABSTRACT: Contralaterally evoked transient otoacoustic emissions (CETOAEs) were recorded from 10 normal-hearing young adults (20 ears) in response to monaural, 11/s, 65 dB pe SPL clicks to the ear contralateral to the microphone probe. A burst of CETOAEs was observed 12-22 ms (average peak at 18.5 ms) after the contralateral click, and its mean level was -7.3 dB pe SPL, 4 dB above the averaged noise level. The frequency content of CETOAEs included a prominence around 1 kHz. In 40% of the ears examined CETOAEs were 3 dB or more above noise level in both replications of records from the same ear. To explain these results CETOAEs are suggested to reflect mechanical events induced by the crossed efferent system in the cochlea that was contralateral to the stimulated ear. The latency of the contralateral responses suggests that they may be related to the contralateral suppression effect observed with binaural stimulation. The latency of the response, coupled with the anatomical origin of the crossed efferent system at the superior olivary complex, suggest its involvement in the contralateral CETOAEs reported here.
    Hearing Research 02/1998; 115(1-2):39-44. DOI:10.1016/S0378-5955(97)00178-0 · 2.85 Impact Factor
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    Andrey Polyakov, Hillel Pratt
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    ABSTRACT: The binaural interaction components (BIC) of the human auditory brainstem responses have been associated with sound lateralization which involves analyzing correlated inputs from the two ears. To test the hypothesis that BIC generators are specifically sensitive to binaural, correlated sounds, the effects of monaural and binaural correlated and uncorrelated masking on BIC to clicks were compared. Analysis included peak-to-prestimulus baseline amplitudes and latencies of BIC peaks from the vertex-mastoid ('A') and vertex-neck ('Z') channels, as well as the three-channel Lissajous trajectory (3-CLT) measures. Trajectory amplitudes of BIC BdIII, BeI and BeII were significantly suppressed by correlated (but not by uncorrelated) binaural noise, when compared with the unmasked condition. Moreover, component BdIII was more affected by masking with correlated than with uncorrelated binaural noise. Overall, binaural noise was more effective in suppressing BIC then monaural noise, and interaurally correlated binaural noise was more effective than uncorrelated binaural noise. These results are compatible with BIC generation by a binaurally activated subset of central auditory neurones which is sensitive to interaurally correlated sounds. Such a subset has been associated with the superior olivary complex and is assumed to be involved in sound lateralization.
    Audiology: official organ of the International Society of Audiology 01/1998; 37(1):17-26. DOI:10.3109/00206099809072958
  • Yongbing Shi, Andrey Polyakov, Hillel Pratt
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    ABSTRACT: Monaural and binaural 11/s, 65 dB pe SPL clicks with interaural time and intensity disparities known to affect central auditory processing were used to study contralateral suppression of transient evoked otoacoustic emissions (TEOAEs) in 10 subjects (20 ears). Psychophysical assessment of sound lateralization induced by the same stimuli was also conducted. TEOAEs were recorded to monaural (ipsilateral to the OAE recording probe) and to binaural clicks when clicks to the contralateral ear were synchronous and symmetrical in intensity, or, in the binaural intensity disparity conditions, synchronous but 10 dB higher or 10 dB lower in the ear contralateral to the OAE recording probe. When interaural time disparities were studied, the clicks to the contralateral ear were of the same intensity throughout, but 400 micros earlier or 400 micros later than to the ear with the probe. The TEOAE components at 13-15.8 ms showed suppression, relative to monaural responses, under all binaural conditions. This contralateral suppression did not correlate with the psychophysical findings. Suppression effects were more pronounced with binaural disparity than with binaurally symmetrical clicks. Thus, although contralateral click intensity was the same with time disparities, suppression was paradoxically enhanced compared to the binaurally symmetrical stimulation. To explain these results we propose that two factors are involved in TEOAE suppression with binaural clicks: (1) contralateral intensity and (2) interaural disparity (time or intensity). The latency of the suppressions observed, the effect of interaural disparity on these suppressions, coupled with the anatomical origin of the crossed efferent fibers and the disparity sensitivity of the superior olivary complex (SOC), all suggest SOC involvement in these TEOAE suppressions.
    Hearing Research 09/1997; 110(1-2):259-65. DOI:10.1016/S0378-5955(97)00088-9 · 2.85 Impact Factor
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    Hillel Pratt, Andrey Polyakov, Leonid Kontorovich
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    ABSTRACT: Sound lateralization can be induced by interaural intensity disparities (IIDs) or by interaural temporal disparities (ITDs). The purpose of this study was to indicate whether IIDs and ITDs are processed by the same central units that detect interaural disparity in timing of afferent activity. If sound lateralization to intensity and time cues was determined by the same afferent latency disparity detectors in the brainstem, lateralization would be the same, regardless of whether latency disparity was induced by IIDs or ITDs. Moreover, the disparity detectors, and thus their dipole equivalents, would be the same for equal lateralizations, whether induced by IIDs or ITDs. Auditory brainstem evoked potentials (ABEPs) were recorded in response to monaural and binaural clicks, with a variety of IIDs and ITDs. Peak II (proximal auditory nerve activity), peak III (input to the superior olivary complex), and binaural interaction components (BICs) BeI and BeII (binaurally activated upper pons) were identified and their latencies measured. The psychophysical lateralization of the clicks (in cm from vertex) was also measured in response to the same binaural stimuli. The correlations between interaural afferent latency disparities (difference in corresponding peak latencies originating in each ear) and psychophysical click lateralization were calculated. Similarly, the correlations with click lateralization of the BICs equivalent dipole latency as well as orientation change (relative to symmetrical clicks) were determined. A strong correlation with lateralization was found for peaks II and III latency disparities, with steeper slopes for IIDs than for ITDs. Moreover, binaural activity across the same lateralizations differed between IIDs and ITDs. These results, therefore, indicate that interaural time and intensity cues are processed by separate systems in the brainstem, both at the afferent convergence level and after interaural disparities are determined.
    Hearing Research 07/1997; 108(1-2):1-8. DOI:10.1016/S0378-5955(97)00033-6 · 2.85 Impact Factor
  • Andrey Polyakov, Hillel Pratt
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    ABSTRACT: Three-channel Lissajous' trajectories (3-CLT) of the binaural interaction (BI) in auditory brainstem evoked potentials (ABEP) were derived from 13 normally and symmetrically hearing adults by subtracting the response to binaural clicks from the algebraic sum of monaural responses. ABEPs were recorded from four channels, three of them orthonormal to each other, in response to alternating polarity clicks, presented at a rate of 11/s with interaural time differences (ITD) of 0.2, 0.4 and 1.0 ms and an intensity of 65 dB nHL, or isochronic to both ears with interaural intensity differences (IIDs) of 5, 10 and 15 dB (65 dB nHL +/- 2.5, 5.0 and 7.5 dB, respectively). All 3-CLTs included 6 planar segments (labeled BdI, BdII, BdIII, BeI, BeII and Bf). Amplitudes of 3-CLT BI components were not significantly affected by increasing ITDs and IIDs, but latencies of all components increased significantly. The most remarkable finding was a significant change in apex orientations of BeI and BeII of the BI 3-CLT across stimulus conditions. The changes in BeI and BeII apex orientations, across stimulus conditions, may reflect differences in the anatomical representation of activity evoked by differently lateralized sounds. We suggest that this may indicate spatio-topic organization in the human brainstem.
    Hearing Research 06/1996; 94(1-2):107-15. DOI:10.1016/0378-5955(96)00009-3 · 2.85 Impact Factor
  • Andrey Polyakov, Hillel Pratt
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    ABSTRACT: Three-channel Lissajous' trajectories (3-CLTs) of the binaural interaction component (BI) of auditory middle latency evoked potentials (AMLEPs) were derived from 14 normally hearing adults by subtracting the response to binaural clicks from the algebraic sum of monaural responses. AMLEPs were recorded in response to 65 dB nHL, rarefaction clicks, presented at a rate of 3.3/s. A normative set of BI 3-CLT measures was calculated and compared with the corresponding measures of simultaneously recorded, single-channel vertex-left mastoid and vertex-neck derivations of BI and of AMLEP to binaural stimulation (B). 3-CLT measures included: apex latency, amplitude and orientation, as well as planar segment duration, orientation, size and shape. The results showed seven main apices and associated planar segments ('Be', 'Bf', 'Bg', 'Bh', 'Bi1', 'Bi2' and 'Bj') in the 3-CLT of BI. Apex latencies of the BI 3-CLT were comparable to peak latencies of the vertex-left mastoid and vertex-neck AMLEP and BI records, both in their absolute values and in intersubject variability. Durations of BI planar segments were approximately 5.0 ms. Apex amplitudes of BI 3-CLT were larger than the respective peak amplitudes of the vertex-mastoid and vertex-neck BI records, while their intersubject variabilities were comparable. The lateralization of BI components may indicate asymmetric processing of binaural auditory input, or may be connected with anatomical asymmetry such as skull thickness. Preliminary analyses did not reveal a clear correlation between the lateralization of the BI component 'Bi2' and the handedness of the subject. We suggest that BI components of AMLEP may be associated with the primary auditory cortex and subcortical ascending structures.
    Hearing Research 03/1995; 82(2):205-15. DOI:10.1016/0378-5955(94)00178-S · 2.85 Impact Factor
  • Andrey Polyakov, Hillel Pratt
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    ABSTRACT: Three-channel Lissajous trajectories (3-CLTs) of binaural interaction components (BI) of auditory brainstem potentials (ABEPs) were derived from 13 normally hearing adults by subtracting the response to binaural clicks from the algebraic sum of monaurally evoked responses to clicks. ABEPs were recorded in response to 65 dB nHL, alternating-polarity clicks, presented at a rate of 11/s. The procedure was repeated with clicks alone as well as with clicks with broad-band masking noise. Noise was presented at 25 and 45 dB nHL, producing a signal-to-noise ratio of +40 and +20 dB, respectively. All BI 3-CLTs included 6 planar segments (labeled BdI, BdII, BdIII, BeI, BeII and Bf) whose apex latencies, except Bf, increased with increasing noise level above 25 dB nHL, and whose durations, sizes, shapes and orientations did not change across noise levels. There were also significant increases in peak latencies of the BI from single channels vertex-mastoid and vertex-neck with increasing noise level. No significant change was found in the trajectory amplitude of apices, with the exception of apices BdIII and Bf whose amplitudes increased with increasing noise level. We suggest that the paradoxical increase in BI amplitude with masking noise may reflect a binaural enhancement of the effect of noise. The effects observed indicate that, whereas the response to clicks displays occlusion, the response to noise displays spatial facilitation at the brainstem level.
    Audiology: official organ of the International Society of Audiology 01/1995; 34(1):36-46. DOI:10.3109/00206099509071897
  • Andrey Polyakov, Hillel Pratt
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    ABSTRACT: Objective: We provide the normative values for middle latency auditory evoked potentials (MLAEPs) measures (three-channel Lissajous' trajectories or 3-CLT) in response to clicks and tone pips, which are the stimuli most widely used in MLAEP clinical testing. The relationship of 3-CLT measures to the more widely used latency and amplitude characteristics of the single-channel MLAEP of the same subjects was also evaluated. We further relate the 3-CLT findings to the question of MLAEP generators. Design: 3-CLT of MLAEPs were derived from 12 humans (24 ears) in response to 65 dB nHL, rarefaction clicks as well as tone pips (1000 Hz), presented at a rate of 3.3/sec. A normative set of 3-CLT measures was calculated and compared with the corresponding measures of simultaneously recorded, single-channel vertex-left mastoid and vertex-neck derivation of MLAEP. Results: Apex latencies of 3-CLT were comparable to peak latencies of the vertex-neck record, both in absolute values and in intersubject variability. Durations of planar segments were approximately 5.0 msec. Size and shape measures of planar segments were variable across subjects, making their clinical use, in their present form, questionable. Conclusions: The results showed two apices and associated planar segments (i1 and i2) in the 3-CLT of MLAEP which corresponded to the vertex-neck component Pa. These results and earlier studies that indicated a dual set of generators for Pa are compatible with a primary auditory cortex generator for i1 and ascending subcortical generators for i2.
    Ear and Hearing 10/1994; 15(5):390-399. DOI:10.1097/00003446-199410000-00006 · 2.83 Impact Factor
  • Andrey Polyakov, Hillel Pratt
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    ABSTRACT: The 3-channel Lissajous' trajectory (3-CLT) of the binaural interaction components (BI) in auditory brain-stem evoked potentials (ABEPs) was derived from 17 normally hearing adults by subtracting the response to binaural clicks (B) from the algebraic sum of monaural responses (L + R). ABEPs were recorded in response to 65 dB nHL, alternating polarity clicks, presented at a rate of 11/sec. A normative set of BI 3-CLT measures was calculated and compared with the corresponding measures of simultaneously recorded, single-channel vertex-left mastoid and vertex-neck derivations of BI and of ABEP L + R and B. 3-CLT measures included: apex latency, amplitude and orientation, as well as planar segment duration and orientation. The results showed 3 apices and associated planar segments ("BdII," "Be" and "Bf") in the 3-CLT of BI which corresponded in latency to the vertex-mastoid and vertex-neck peaks IIIn, V and VI of ABEP L + R and B. These apices corresponded in latency and orientation to apices of the 3-CLT of ABEP L + R and ABEP B. This correspondence suggests generators of the BI components between the trapezoid body and the inferior colliculus output. Durations of BI planar segments were approximately 1.0 msec. Apex amplitudes of BI 3-CLT were larger than the respective peak amplitudes of the vertex-mastoid and vertex-neck recorded BI, while their intersubject variabilities were comparable.
    Electroencephalography and Clinical Neurophysiology 10/1994; 92(5):396-404. DOI:10.1016/0168-5597(94)90016-7
  • Andrey Polyakov, Hillet Pratt
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    ABSTRACT: Three-channel Lissajous trajectories (3-CLTs) of the binaural interaction components of the auditory brainstem-evoked potentials were recorded from 17 adult subjects in response to rarefaction, condensation and alternating polarity clicks. All 3-CLTs included 3 planar segments (named Bd, Be and Bf) whose latencies, amplitudes, orientations, sizes and shapes were not affected by click polarity. A significant increase was found in the duration of planar segment Be to alternating polarity clicks. This effect may be explained by limitations of spatiotemporal resolution of the method, which did not allow distinction of contributions from temporally overlapping generators participating in binaural processing.
    Audiology: official organ of the International Society of Audiology 01/1994; 33(5):264-73. DOI:10.3109/00206099409071886