[Specific features of lateralization of a stationary auditory image by a human under condition of stimulation without interaural differences: a neurophysiological analysis].

Analysis of the lateralization phenomena of a fused auditory image (FAI) was performed on the basis of the previously developed model of the binaural directional hearing. It was found earlier that, under conditions of auditory stimulation without interaural differences, the FAI was localized at the head midline only in about a quarter of subjects. In a greater part of the listeners, the FAI was lateralized within the range of -4.6 ... +11.2 degrees from the midline. It was shown that FAI localization with reference to the head midline may be determined by the extent of asymmetry and spatial contrast between the "active" neural zones in the left and right halves of the subjective auditory space. In turn, the asymmetry (or its absence) of these "active" zones fully depends on a distribution of neurons by characteristic time delays in the left and right halves of the subjective auditory field. The model also explains the fact of a decrease in localization precision with the FAI position just at the midline.

Tonic organization of the inferior colliculi in the cat in conditions of simulated sound source motion.

Simulation of the motion of a sound source using a series of clicks with variable interaural delays was used to study movement effects as changes in the amplitude of sequential focal evoked potentials (EP) in series of EP arising in response to the signal. These experiments showed that a) in 25% of cases the movement effect depended on the direction of the simulated motion; b) the movement effect was better represented on the wide ipsilateral to the site of EP recording; left- and right-sided movement effects were identically dependent on the rate of motion; c) the phenomenon of the movement effect was associated with the dominance of contralateral afferentation compared with ipsilateral afferentation; d) the movement effect was accompanied by inhibitory manifestations consisting of suppression of monaural afferentation in conditions of binaural stimulation; e) marked movement effects were seen mainly in the ventrocentral part of the central nucleus, located very close to the positions of large multipolar neurons, while mild and moderate movement effects were distributed quite uniformly though the volume of the nucleus, following the distribution of the "basic" neurons; it is suggested that movement effects of different strengths are associated with differences in the ratios of the effectivenesses of ipsi- and contralateral stimulation, which depend on the properties of multipolar and "basic" neurons in the central nucleus of the inferior colliculus in relation to their responses to ipsi- and contralateral stimulation.

[Topical organization of the cat inferior colliculus under conditions of the simulated sound source motion]. / Topicheskaia organizatsiia zadnikh kholmov mozga koshki v usloviiakh imitiruemogo dvizheniia istochnika zvuka.

Binaurally presented click trains with gradually changing ITDs were used to imitate the sound source motion. Focal EP-trains from the cat inferior colliculus, IC, were recorded, and changing amplitude of the successive EPs following successive clicks was taken for estimation of the motion effect (ME). It was shown that a) in 25% of cases the ME depends on the motion direction; b) the ME is better presented ipsilaterally in respect to the recording point, with equal dependence on motion velocity both on the left and on the right; c) the ME phenomenon is connected with prevalence of contralateral afferentation as compared to the ipsilateral one; d) the ME is connected with inhibitory phenomena such as binaural suppression of monaural afferentation; e) the ME of the best amplitude is most pronounced in the ventrolateral area of the IC central nucleus, its localisation being near to that of the great multipolar neurones, whereas slightly and moderately pronounced MEs are presented rather uniformly over the central nucleus like the "basic" neurones are; MEs of different pronouncement are supposed to depend differently on effectiveness of ipsi- and contralateral stimulation--in accordance with properties of multipolar and "basic" neurons.

[A rush technique for the initial assessment of hearing disorders in pre-school and school children]. / Ekspress-metod dlia pervichnoi otsenki narushenii slukha u detei doshkol'nogo i shkol'nogo vozrasta.

A method is proposed for rapid quantitative estimation of auditory sensitivity in children. The method is based on wideband sound signals with short rise time of the amplitude (click trains) used as stimuli under conditions of organized attention of children towards sounds of both high and low (near-threshold) intensities. The method is applicable on equipment made in Russia and is cost-effective.

[The reflection of the simulated movement of a sound source in the evoked potentials of the inferior colliculus in the cat]. / Otrazhenie imitiruemogo dvizheniia istochnika zvuka v vyzvannykh potentsialakh zadnego kholma koshki.

EP series from the cat's inferior colliculus were recorded following binaural stimulation with click series imitating sound source movement due to variation of the interaural time delay (and thus evoking in man the sensation of the moving fused auditory image, FI). The "movement effect" was evaluated as the change in the EP amplitude during the series. The movement effect itself as well as its predominance under conditions of the ipsilateral FI movement as compared to those of the contralateral movement, proved to be connected with greater effectiveness of the contralateral stimulation relative the ipsilateral one.

Different phase sensitivity of low- and high-frequency neurons from the cat's cochlear nucleus.

When tested with two-tone signals while varying the phase value (omega 2) of the second harmonic, the low-frequency neurons (CFs from 0.8 to 5 kHz) showed one maximum and one minimum of the response value over the omega 2-range of 360 degrees. The high-frequency neurons (CFs from 11.5 to 38.5 kHz) showed two maxima and two minima under the same conditions. In addition, the high-frequency neurons, unlike the low-frequency ones, showed no difference in response to click series of opposite polarities. The data are considered in connection with processes of excitation in the low- and high-frequency regions of the cochlea.

Off-responses in the auditory system in relation to the signal end phase and neuronal characteristic frequency.

Off-responses of single neurons from the inferior colliculus (IC) as well as summed off-responses (evoked potentials) from the IC, cochlear nucleus and auditory nerve were studied while varying the end phase of tonal signals. It was found that with tonal signals higher than the characteristic frequency, off-responses at all the auditory levels studied were greatest at the end phases near 0 and 180 degrees and were of minimal value at the end phases near 90 and 270 degrees. On the contrary, with tonal signals lower than the characteristic frequency, the greatest off-responses corresponded to the end phases near 90 and 270 degrees, and responses of the lowest value were registered at the end phases near 0 and 180 degrees. The observed phenomena did not result from transient 'off'-responses of the acoustic system. It is suggested that they reflect certain cochlear processes connected with different effectiveness of oscillation phases at frequencies below and above the resonance.

[Reflection of the characteristics of acoustic signals in the summary synchronized responses of neurons of the auditory system of the cat]. / Otrazhenie kharakteristik zvukovykh signalov v summarnykh sinkhronizovannykh otvetakh neironov slukhovoi sistemy koshki.

Experiments on anesthetized cats have shown that the frequency following response (FFR) which is typical of the lower regions of the auditory system (including the inferior colliculus) may reflect all basic properties of the auditory stimuli. The amplitude and the wave-form of the FFR depend greatly on frequency and intensity of the stimuli, their wave-form and periodicity, masking by noise, as well as interaural differences in stimulation modelling different spatial positions of the sound source.

[Monaural phasic sensitivity of auditory system neurons in the cat]. / Monaural'naia fazovaia chuvstvitel'nost' neironov slukhovoi sistemy koshki.

During monaural stimulation, studies have been made of impulse reactions in neurons from the cochlear nucleus and inferior colluculus to changes in the phase value (psi) of one of the harmonics in two-tone signals. It was shown that about 70% of the neurons from the cochleaur nucleus with a tonic discharge pattern may sharply change their activity (from maximum one up to a complete inhibition) due to changes in psi value. Unlike the cochlear nucleus units, neurons from the inferior colliculus change their tonic or burst-like activity rather seldomly and to a slight extent. At the same time, their phasic on- and especially off-responses exhibit high sensitivity to changes in psi value.

The pattern of response of the inferior colliculus of the cat during the movement of a sound source.

During the application of a train of clicks simulating the movement of a sound source, evoked potentials (EP) of the inferior colliculus gradually changed their amplitude and form ("the movement effect") in 82% of the instances tested. The expression of the ipsilateral movement effect was on the average 1.5 times greater than the contralateral. The movement effect was observed over a wide range of velocities; but, in 65% of the instances, the effect was observed at movement velocities not less than 3.5 rad/sec. Velocities higher than 6.8 rad/sec were most effective in 78% of the instances. Differences in responses were discovered in 26% of the instances involving opposite directions of sound source movement. The movement effect depended substantially upon the site of the EP sampling.

[Overall synchronized response of the inferior colliculi to lateralization of complex sounds]. / Summarnyi sinkhronizirovannyi otvet zadnikh kholmov lateralizatsii slozhnykh zvukov.

Interaural differences in time, intensity or phase introduced into a different frequency component of complex sounds results in changes of amplitude and form of the frequency following response depending on the frequency and phase ranges of the sounds. This relationship may be due to physical differences in stimulation of both ears, i. e. to differences in the sound wave forms and, consequently, in conditions of the convergence of both monaural afferent inflows.

[Spatial characteristics of the reaction of the inferior colliculi in the cat to movement of the sound source]. / Prostranstvennaia kharakteristika reaktsii zadnikh kholmov koshki na dvizhenie istochnika zvuka.

The EP-series response of the inferior colliculus to clicks simulating sound source motion, reflects characteristics of this "motion" ("the motion effect", ME). ME distribution over the inferior colliculus practically coincided with the spatial distribution in cases when contralateral stimulation was more effective than the ipsilateral one. The spatial distribution in cases with no ME was identical with the distribution of cases of equal effectiveness of the contra and ipsilateral stimulations. The ME was shown to be connected with the binaural inhibitory effects and might probably be related to the activity of two main neuronal groups (the principal and multipolar ones).

[Patterns of the reaction of the inferior colliculus to the movement of a sound source in the cat]. / K izucheniiu zakonomernostei reaktsii zadnikh kholmov koshki na dvizhenie istochnika zvuka.

Series of slicks simulating source sound movement caused 82% of the posterior colliculus' EPs to alter gradually their amplitude and/or shape ("the movement effect"). The markedness of ipsilateral effect was about 1.5 times higher than that of the contralateral one. The effect occurred within large range of velocities: no lower than 3.4 rad/sec in 65% of observations. The most effective were the velocities over 6.8 rad/sec in 78%. Difference in responses to opposite directions of the sound source movement occurred in 26%. The movement effect obviously depended on the site of EP recording.