[Motion-Onset Responses During Active and Passive Listening to the Moving Sound Stimuli].

This study investigated the energy-onset and motion-onset responses (N1, P2, cN 1 and cP2 components of the auditory evoked potential) elicited by moving sound stimuli in the passive and active listening conditions. In the passive conditions the subjects were distracted from auditory information; in active conditions they lo- calized the starting and final points of the stimulus trajectory. The sound movement to the left/right from the head midline was produced by linear-changes of the interaural time delay (ITD). The onset of motion was preceded by stationary sound located near the head midline. In the active conditions, the NI component was higher and the P2 component was higher and peaked later as compared to the passive listening. The early and later parts of the motion-onset response (cN 1 and cP2) also were larger in magnitude and peaked later during active listening. Both in active and passive conditions, cNI and cP2 amplitude exhibited increase and latency showed decrease when the stimulus velocity increased. Contralateral asymmetry was found only in the mo- tion-onset responses recorded from the left hemisphere.

[Topography of the Event-Related Brain Responses during Discrimination of Auditory Motion in Humans].

The present study investigates the hemispheric asymmetry of auditory event-related potentials (ERPs) and mismatch negativity (MMN) during passive discrimination of the moving sound stimuli presented according to the oddball paradigm. The sound movement to the left/right from the head midline was produced by linear changes of the interaural time delay (ITD). It was found that the right-hemispheric N1 and P2 responses were more prominent than the left-hemispheric ones, especially in the fronto-lateral region. On the contrary, N250 and MMN responses demonstrated contralateral dominance in the fronto-lateral and fronto-medial regions. Direction of sound motion had no significant effect on the ERP or MMN topography. The right-hemispheric asymmetry of N1 increased with sound velocity. Maximal asymmetry of P2 was obtained with short stimulus trajectories. The contralateral bias of N250 and MMN increased with the spatial difference between standard and deviant stimuli. The results showed different type of hemispheric asymmetry for the early and late ERP components which could reflect the activity of distinct neural populations involved in the sensory and cognitive processing of the auditory input.

[Sensitivity of the hearing system to the velocity of auditory motion: difference thresholds and mismatch negativity].

The parallel psychophysical and MMN study focused at the sensitivity of human hearing system to variations in velocity of sound image movement. The motion of sound stimuli with various velocities in the 450 deg/s to 732 deg/s range in increments of 6 deg/s to the left or to the right from the head midline was simulated by introducing linear changes of interaural delay into dichotic stimuli. The psychophysical experiments were designed according to the 2-alternative forced choice paradigm. The subjects were presented by pairs of moving stimuli and were asked to decide which moved faster. The stimuli created for the present study ensured that the subjects performed the discrimination task without relying on associated cues of sound displacement or duration. The psychophysical measures were compared with electrophysiological indexes of sound processing (auditory evoked responses (ERPs) and mismatch negativity (MMN)). Significant MMN was elicited by the difference of 170 deg/s between the reference and test velocity, which corresponded to the relative velocity increase of 38%. At the same time, the difference thresholds for velocity were much higher and exceeded 50%. The results suggest that MMN magnitude depended on the velocity difference between standard and deviant stimuli and was more sensitive to velocity difference than psychophysical measure.

[Objective and subjective indexes of auditory motion processing].

The study focused at the objective and subjective indexes of human hearing system sensitivity towards different types of moving sound stimuli. The experiment employed two methods: electrophysiological (MMN recording) and psychophysical method (two-alternative forced choice). Two types of spatial sound stimuli simulated gradual and abrupt sound motion from the head midline. MMN as an objective index of spatial discrimination has been obtained in response to the subthreshold and the suprathreshold stimuli. An increase of trajectory length of the moving stimuli resulted in an increase of the MMN amplitude and of subjective discrimination as well, although their correlation remained below the significance level. The results obtained are discussed from the point of view of preconscious perception of auditory spatial information.

[Perceptual categories for auditory motion as reflected in mismatch negativity].

Auditory evoked response and mismatch negativity potential have been studied using the reversed odd-ball paradigm of standard and deviant stimulus presentation. In the experiments, three types of spatial sound stimuli (stationary and moving either gradually or abruptly from the head midline) were presented in three configurations. Each configuration employed one stimulus type as standard and the other two types as deviants. It was demonstrated that the configuration reversals influenced significantly the evoked response and mismatch negativity. The results obtained are discussed as the possible evidence of the categorical perception of auditory motion revealed at the earlier stages of sound processing in the hearing system.

[Evaluation by humans of signals modulating different sound movement directions and particulars of perception of such signals in patients with temporal epilepsy].

In patients with epileptic lesions in the hippocampus as well as in the temporal lobe and hippocampus simultaneously, studies were made on the perception of sound signals imitating sound source movement. It was established that hippocampal lesion results in disturbance of estimation of sound spatial characteristics which manifests in a change accuracy of localization and shortening of subjective sound image movement trajectory. Maximum disturbances of localization function are observed during lesions of hippocampus and temporal lobe. Possible neurophysiological mechanism underling observed disturbances are considered.

[Event-related potentials of human brain in spatial hearing].

The review presents the data concerning auditory event-related potentials and their "mismatch negativity" component under conditions of stationary and moving sound source localization. Both free-field and dichotic experimental conditions are considered. The interhemispheric asymmetry of the brain responses elicited by the sound sources of various spatial properties is also discussed.

Lateralization of brain responses to auditory motion: A study using single-trial analysis.

The present study investigates hemispheric asymmetry of the ERPs and low-frequency oscillatory responses evoked in both hemispheres of the brain by the sound stimuli with delayed onset of motion. EEG was recorded for three patterns of sound motion produced by changes in interaural time differences. Event-related spectral perturbation (ERSP) and inter-trial phase coherence (ITC) were computed from the time-frequency decomposition of EEG signals. The participants either read books of their choice (passive listening) or indicated the sound trajectories perceived using a graphic tablet (active listening). Our goal was to find out whether the lateralization of the motion-onset response (MOR) and oscillatory responses to sound motion were more consistent with the right-hemispheric dominance, contralateral or neglect model of interhemispheric asymmetry. Apparent dominance of the right hemisphere was found only in the ERSP responses. Stronger contralaterality of the left hemisphere corresponding to the "neglect model" of asymmetry was shown by the MOR components and by the phase coherence of the delta-alpha oscillations. Velocity and attention did not change consistently the interhemispheric asymmetry of both the MOR and the oscillatory responses. Our findings demonstrate how the lateralization pattern shown by the MOR potential was interrelated with that of the motion-related single-trial measures.

Hemispheric asymmetry of ERPs and MMNs evoked by slow, fast and abrupt auditory motion.

The current MMN study investigates whether brain lateralization during automatic discrimination of sound stimuli moving at different velocities is consistent with one of the three models of asymmetry: the right-hemispheric dominance model, the contralateral dominance model, or the neglect model. Auditory event-related potentials (ERPs) were recorded for three patterns of sound motion produced by linear or abrupt changes of interaural time differences. The slow motion (450deg/s) was used as standard, and the fast motion (620deg/s) and the abrupt sound shift served as deviants in the oddball blocks. All stimuli had the same onset/offset spatial positions. We compared the effects of the recording side (left, right) and of the direction of sound displacement (ipsi- or contralateral with reference to the side of recording) on the ERPs and mismatch negativity (MMN). Our results indicated different patterns of asymmetry for the ERPs and MMN responses. The ERPs showed a velocity-independent right-hemispheric dominance that emerged at the descending limb of N1 wave (at around 120-160ms) and could be related to overall context of the preattentive spatial perception. The MMNs elicited in the left hemisphere (at around 230-270ms) exhibited a contralateral dominance, whereas the right-hemispheric MMNs were insensitive to the direction of sound displacement. These differences in contralaterality between MMN responses produced by the left and the right hemisphere favour the neglect model of the preattentive motion processing indexed by MMN.

[ACTIVE AND PASSIVE DISCRIMINATION OF MOVING SOUNDS: RHYTHMIC ACTIVITY OF HUMAN BRAIN].

The spectral dynamics of the EEG rhythmicity during active and passive discrimination of stationary and moving sound stimuli presented according to the oddball paradigm were investigated. Standard stimuli represented stationary midline sounds. Deviant stimuli simulated smooth and stepwise sound source motion (to the left/right from head midline) produced by linear and stepwise changes of interaural time delay. Significant changes of the brain oscillations were found in the frequency range of 3-30 Hz. The dynamics of the moving deviant stimuli (smooth vs. stepwise) had greater impact on theta-rhythm power in active listening conditions: a stronger theta-power increase was evoked by the stepwise sound motion as compared to smooth motion. Significant increase in theta-power was also observed with rightward sound displacement as compared to leftward displacements. Active deviant discrimination reduced alpha-power (8-11 Hz) mostly during smooth deviant motion. The power increase of lower alpha-oscillations (12-15 Hz) was stronger with step- wise motion than with smooth motion of deviants. The interhemispheric asymmetry of beta-power decrease in active conditions (as compared to passive) was found in the whole beta-range. The sup- pression of beta-power was stronger at the right hemisphere than at the midline or left hemisphere and showed no dependence on spatial properties of the deviant stimuli. This asymmetry may be related to selective attention to task-relevant sounds and with preparation to motor response. Generally, active auditory discrimination resulted in stronger deviant-related changes of the wide-ranged EEG spectral power than passive discrimination with attentional tuning to task-irrelevant stimuli.

[ACTIVE AND PASSIVE DISCRIMINATION OF MOVING SOUNDS: EVENT-RELATED RESPONSES OF HUMAN BRAIN].

The current study investigates auditory event-related potentials (ERPs) and mismatch negativity (MMN) during active and passive discrimination of stationary and moving sound stimuli presented according to the oddball paradigm. Standard stimuli represented stationary midline sounds. Deviant stimuli simulated sound source location shifts (to the left/right from head midline) produced by linear or stepwise changes of interaural time delay (ITD). The event-related responses were evaluated by peak amplitudes of N1 waves and mean amplitudes of MMN, P3a, P3b and reorienting negativity (RON) components. The N1 amplitude was larger in active than in passive conditions, and was unaffected by spatial dynamic changes of the deviant stimuli. The deviant motion pattern (smooth or stepwise) affected only MMN and RON obtained in passive listening conditions. Abrupt deviant displacement elicited larger MMN and RON components than smooth motion. Drawing listeners' attention to the deviant stimuli resulted in suppression of MMN/RON sensitivity to auditory motion pattern.

Contextual effects on preattentive processing of sound motion as revealed by spatial MMN.

The magnitude of spatial distance between sound stimuli is critically important for their preattentive discrimination, yet the effect of stimulus context on auditory motion processing is not clear. This study investigated the effects of acoustical change and stimulus context on preattentive spatial change detection. Auditory event-related potentials (ERPs) were recorded for stationary midline noises and two patterns of sound motion produced by linear or abrupt changes of interaural time differences. Each of the three types of stimuli was used as standard or deviant in different blocks. Context effects on mismatch negativity (MMN) elicited by stationary and moving sound stimuli were investigated by reversing the role of standard and deviant stimuli, while the acoustical stimulus parameters were kept the same. That is, MMN amplitudes were calculated by subtracting ERPs to identical stimuli presented as standard in one block and deviant in another block. In contrast, effects of acoustical change on MMN amplitudes were calculated by subtracting ERPs of standards and deviants presented within the same block. Preattentive discrimination of moving and stationary sounds indexed by MMN was strongly dependent on the stimulus context. Higher MMNs were produced in oddball configurations where deviance represented increments of the sound velocity, as compared to configurations with velocity decrements. The effect of standard-deviant reversal was more pronounced with the abrupt sound displacement than with gradual sound motion.

Properties of derived cochlear action potentials in forward tonal masking in guinea pigs.

Chronic experiments on guinea pigs were used to study the characteristics of cochlear nerve action potentials and the derived potential in conditions of forward masking. The auditory nerve action potential was recorded from the round window of the cochlea. The derived potential was obtained by subtracting the action potential recorded with masking from the response obtained in silence. These studies showed that the derived potential showed higher sensitivity to masking than the traditional measure of masking, i.e., the decrement in the amplitude of the auditory nerve action potential. The derived potential reflects not only changes in the action potential during masking, but also changes in its shape. Differences between the derived potential and the action potential decrement provide evidence that the amplitude and time changes in the derived potential provide more complete information on the nature of activity in the auditory fibers.

Responses of cat primary auditory cortex neurons to moving stimuli with dynamically changing interaural delays.

The spike responses of individual neurons in the primary auditory cortex were studied in anesthetized cats during exposure to stationary and moving stimuli with static or dynamically changing interaural delays (deltaT). Static stimuli were tones and clicks. Dynamic stimuli were created using series of synphase and antiphase clicks with interaural delays which changed over time. Sensitivity to changes in deltaT was predominantly present in neurons with low characteristic frequencies (less than 2.8 kHz). Changes in deltaT in moving stimuli induced responses in neurons sensitive to changes in deltaT in the stationary stimulus. The effect of movement could be a relationship between the level of spike activity and the direction and rate of change of deltaT or it could be a displacement of the tuning curve for the response to deltaT (the deltaT function) in the direction opposite to that of the direction of the change in deltaT. The magnitude of the effects of movement depended on the position of the period for changes in deltaT relative to the deltaT function. The greatest effects were seen with changes in deltaT on the sloping part of the deltaT function.

Comparison of binaural release from forward masking in animals and humans. Electrophysiological studies.

Evoked potentials in the inferior colliculus and auditory areas of the cortex were studied in anesthetized guinea pigs and long-latency auditory evoked potentials (LAEP) were studied in waking humans using sequential binaural presentation of pairs of clicks--the masker and the masked signal--with a variable interval between them, to provide the conditions needed for the psychophysical phenomenon of direct forward masking. Introduction of phase differences between the masker and the masked signal led to decreases in suppression of responses to the masked signal and to faster recovery of the reaction types recorded. The greatest relative differences between response magnitudes to antiphase and synphase masked signals were seen at the beginning of the recovery process, and were 1.6, 1.5, and 1.4 respectively for responses from the inferior colliculus, auditory area of the cortex, and LAEP at stimulus intensities of 50-65 dB sound pressure level, differences subsequently decreasing to zero. There was a positive correlation between this measure and the stimulus intensity. The greatest differences between the time at which the recovery process ended for responses to antiphase and synphase masked signals were 4, 250, and about 2000 msec respectively for the inferior colliculus, auditory area of the cortex, and LAEP.

The role of phase changes in sound signals in localization of sound sources.

The auditory system in humans and animals makes virtually no discrimination of phase changes in the structure of monaurally presented sound signals. However, electrophysiological studies have demonstrated marked changes in the responses of the central parts of the auditory system when the phase structure of the signal changes during presentation of the same type of stimulation. We have suggested that this inconsistency is due to the preparative role of phase effects during monaural stimulation for subsequent operations in the auditory system involved in determining the location of a sound source in space. This report presents experimental data on defined changes (increases in amplitude) in the electrical responses of the midbrain center of the auditory system (inferior colliculus) in antiphase binaural presentation of series of sound impulses (comparison with synphase presentation). These changes may be part of the mechanism underlying the interference resistance of the auditory system during determination of the location of a sound source (binaural release from masking). Neuronal cortical activity is sensitive and selective to dynamic interaural changes in the phase spectrum of the signal, which may provide the basis of the mechanism for locating a moving sound source. Auditory evoked potentials in humans demonstrate memorizing of the direction of movement of a sound image, as shown by the changes in parameters on presentation of stimuli of different locations (deviant stimuli) differing from the standard parameters of mismatch negativity.

[Reproduction of the shape of an acoustic wave in the overall synchronized response of the cochlear nuclei]. / Vosproizvedenie formy zvukovoi volny v summarnom sinkhronizirovannom otvete kokhlearnykh iader.

The waveform of the frequency-following response (FFR) of the cat cochleas nuclei stimulated by single tones and two-tone harmonic complexes of low frequencies (less than or equal to 500 Hz) corresponds to periodic sequence of evoked potentials (EP-like waves). The wave-form similarity between FFR and EP disappears at higher frequency tones. The change in the wave-form of the two-tone sound signal resulted in distinct changes both in the amplitude and in the moment of occurrence of the EP-like waves in the FFR. In the presence of the first harmonics, the FFR to the relatively high harmonics (from the 4th to the 6th one) showed augmentation during one half-period of the first harmonic and diminution during the other one.

[Responses of neurons of the inferior colliculus of cats to acoustic signals in the presence of interaural temporal differences in stimulation]. / Reaktsii neironov zadnego kholma koshki na zvukovye signaly pri interaural'nykh vremennykh razlichiiakh stimuliatsii.

In anesthetized cats, neuronal responses in the posterior colliculus to binaural stimulation with series of synphasic and anti-phasic clicks with interaural delay (delta T) changing gradually in time, and to binaural stimulation with tones with different delta T values, were studied. Varying of delta T in the click series induced obvious changes in responses of neurons with optimal frequencies (F0) up to 2.6 kHz. Wide-range change of the delta T made the magnitude of F0 less than or equal to 2.6 kHz neurons responses to clicks and tones the periodic function of delta T. Dependences of the response on delta T were similar for the optimal frequency tones and for the synphasic clicks. The reversed dependence was observed on with of the antiphasic clicks. The data obtained are considered from the standpoint of cochlear mechanisms for sound signals processing.

[Inhibitory processes in neuronal reactions of the auditory cortex in the cat undergoing dichotic stimulation]. / Tormoznye protsessy v reaktsiiakh neironov slukhovoi oblasti kory koshki pri dikhoticheskoi stimuliatsii.

In experiments on anaesthetized cats, studies have been made of intracellular and extracellular responses of single units in the auditory cortex during dichotic stimulation simulating sound source motion. Responses of some cortical units exhibit strong dependence on the signal parameters related to spatial and directional characteristics of simulated sound source motion. Profound inhibition was invariably revealed at the beginning of sonic stimulation as well as during certain moments of its movement. The role of inhibition in formation of cortical reactions to sound source motion is discussed.

[Characteristics of sound source movement perception as a basis for acoustic vertical construction]. / Kharakteristiki vospiiatiia dvizheniia istochnika zvuka kak osnova sozdaniia akusticheskoi vertikali.

The subject of inquiry was perception of moving sound along the vertical at various angular velocities. The sound was switched around by 13 sequential dynamics installed on a 180 degrees arc. Threshold values for discriminating angular velocities at 150, 167, 188, 214, 250, 300, 375, and 500 degrees/s were measured with the minimal borderlines method. Six test-subjects with normal hearing participated in the experiment. Acceleration of sound movement in the range from 167 up to 500 degrees/s leads to essentially linear increases in absolute threshold values and monotonous increases in relative threshold values.