[The cat acoustic cortex response to the signal localised signs under conditions of electrical stimulation of the acoustic nerve and sound stimulation].

The mechanisms underlying acoustic capacity to localize the sound source in horizontal plane were studied. The results obtained are discussed from the aspect of existing ideas of the mechanisms providing the localization acoustic capacities in natural way of stimulation in neuronal activity of the acoustic centres. The data obtained are also considered from the viewpoint of a possible considerable improvement of deaf people's spatial orientation with the aid of bilateral implanted cochlear implants.

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.

Evoked potentials in the cat inferior colliculus during exposure to signals simulating movement of sound sources at different speeds in opposite directions.

The relationships between changes in the amplitudes of evoked potentials (EP) in the inferior colliculus of anesthetized adult cats were studied during presentation of acoustic signals simulating sound sources moving in the azimuthal plane at different speeds and in opposite directions, as well as stationary sound sources. Movement was created by changing the interaural time differences in stimuli between clicks in binaurally presented series of clicks. These studies showed that the amplitude of EP arising as a result of presentation of these signals depended on the speed of movement. The upper border of the range of speeds in which responses to "moving" and stationary signals were different was 320 degrees/sec. Different experiments showed that the greatest difference in responses was seen at movement rates of 67-320 degrees/sec, though most were recorded at speeds of 125 and 170 degrees/sec. Responses to movement in the lateromedial direction, regardless of speed, had greater magnitudes than responses to movement at the same speed in the opposite direction.

[Evoked potentials of the cat inferior colliculus to acoustic stimuli simulating sound source movement with different velocities in opposite directions]. / Vyzvannye potentsialy zadnego kholma koshki pri deistvii signalov, modeliruiushchikh dvizhenie istochnika zvuka s razlichnoi skorost'iu v protivopolozhnykh napravleniiakh.

Amplitude changes of inferior colliculus evoked potentials (EPs) in anaesthetized adult cats were studied under presentation of acoustic stimuli simulating both azimuth-moving and stationary sound source. The movement was simulated with gradual changes of interaural time delay between binaurally presented click trains. It was shown that the amplitude of EPs elicited by "moving" signals depended on the velocity of movement. Amplitude differences between EPs to "moving" and stationary stimuli were observed under motion velocities up to 320 deg./s. The greatest response amplitudes in different experiments took place under velocities within the range of 67-320 deg./s with most of them recorded under velocities of 170 and 125 deg./s. Amplitude of the responses to lateral-medial movement with any velocity were always greater than those to opposite direction of movement with the same velocity.

[Role of phasic changes in sound signal in localization of auditory image]. / Rol' fazovykh izmenenii v zvukovom signale pri lokalizatsii zvukovogo obraza.

The work presents experimental data on certain changes in electrical responses of the auditory system's midbrain centre in a contraphasic binaural presentation of sound impulse series. Neuronal cortical activity is selective in respect to dynamic interaural changes of signals' phasic spectre which may serve as a basis for the mechanisms of localising a moving source of sound. Human auditory evoked potentials reveal a manifestation of memorizing the auditory image movement direction as shown by appearance of stimuli deviant from standard mismatch negativity.

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.

[Comparison of binaural release from forward masking in animals and humans. Electrophysiologic study]. / Sopostavlenie proiavlenii binaural'nogo osvobozhedeniia ot posledovatel'noi maskirovki u zhivotnykh i cheloveka. Elektrofizicheskoe issledovanie.

The EPs of the inferior colliculus and auditory cortex in anaesthetized guinea pigs and the long latency auditory EPs in alert humans were studied. The stimuli consisted of binaurally presented pairs of clicks used as a masker, and the probe, with a variable time delay between them. The greatest relative differences between out-of-phase and in-phase probe responses were observed at the beginning of the recovery course. They averaged as 1.6, 1.5 and 1.4 for the responses of the inferior colliculus, auditory cortex and long latency potentials, resp., at the stimuli intensities of 50-65 dB SPL, and then decreased to zero during the time course of the probe response recovery. Correlation of this parameter with the stimulus intensity was positive.

[Neuronal reactions of the fastigial nucleus in the cat to sound signals]. / Reaktsii neironov fastigial'nogo iadra koshki na zvukovye signaly.

28 out of 67 neurones of the fastigial nucleus responded to sound signals in anesthetized cats. Thresholds of the responses were over 72 dB in most of the neurones. Changes in intensity or duration of the sound signals were followed by insignificant changes in neuronal activity. An insignificant frequency selectivity (Q less than 0.2) was found in 8 (29%) neurones out of the 28. A considerable sensitivity was revealed in respect to the signals simulating spatial location or moving of the sound source. 13 out of 16 neurones (81%) responded to changes in interaural differences of the stimulation in time. Half of these neurones revealed the maximal changes of activity in interaural differences lesser than 50 microseconds (i.e. with the delays simulating the situation of the sound source near the midline of the head). 7 out of 18 neurones (39%) proved to be sensitive to "movement" of the sound source, each neuron having a preferential sensitivity to the movement with a certain speed.

Characteristics of neuronal responses in the sensorimotor cortex of the cat to monaural and binaural stimulation.

The dependence of neuronal responses in the sensorimotor cortex (SMC) of the cat upon localization parameters of dichotically presented auditory signals was studied in acute experiments. Binaural stimulation was more effective than either monaural stimulation. It was shown that spatial-localization parameters of auditory-stimulus source such as interaural differences in intensity and time are reflected by the characteristics of neuronal responses in the SMC; moreover, in 67-88% of cases the most pronounced responses were observed for small, close to zero, temporal and amplitudinal interaural shifts. It was found that SMC neuronal background activity may be altered by signals simulating directed movement of the sound source in the horizontal plane.

[Selectivity of trace reactions of medial geniculate neurons to the rate of simulated movement of a sound source in the cat]. / Izbiratel'nost' sledovykh reaktsii neironov vnutrennego kolenchatogo tela koshki k skorosti imitiruemogo dvizheniia istochnika zvuka.

33 out of 90 neurons of the cat medial geniculate body revealed the selectivity of their afterdischarges to movement of sound when velocity of the movement changed from 30 to 180 deg/s. There was a specific velocity of the movement for each neuron. 76% of the neurons preferred the movement of 45--90 deg/s. 9 neurons had a periodic character of responses. The selective afterdischarges occurred in 39% of dorsal neurons and in 39% of ventral ones. The afterdischarges can be dependent on the direction of sound source movement, too.

[Response of medial geniculate body responses to the velocity of simulated sound source movement in the cat]. / Reaktsii neironov vnutrennego kolenchatogo tela koshki na skorost' imitiruemogo dvizheniia istochnika zvuka.

36 neurons (39%) of the anaesthetized cat medical geniculate body responded to simulated motion of the sound source (with angular velocity of 30 to 180 degrees/sec) selectivity with a certain speed of firing rate changing specific for each neuron during action of the signal. Selective response to a certain velocity of the sound motion occurred in 55% of neurons of the dorsal portion and in 27% of the ventral portion of the medial geniculate body. Response of these neurons reflected the whole range of experimental velocities. 75% of neurons revealed most obvious responses to the sound motion velocity of 30--90%/sec. The selective response to a certain velocity of the sound motion seems to depend on the direction of motion.

[Characteristics of cat sensomotor cortex neuron responses to monaural and binaural stimulation]. / Kharakteristiki reaktsii neironov sensomotornoi kory mozga koshki na monaural'nuiu i binaural'nuiu stimuliatsii.

In cats, the technique of localization parameter of dichotic sounds showed the binaural stimulation to be more effective than the monaural one. The interaural difference in intensity and time modified characteristics of neuronal responses in the sensorymotor cortex (SMC), the responses being most obvious in 67--88% of cases at the minor, approximating zero, temporal and amplitude interaural shifts. The SMC neurons altered their spontaneous activity in response to signals simulating movement of the sound source in horizontal plane. 74% of these neurons seemed to prefer the velocity up to 48 degrees/sec. These features of the SMC neuronal responses can be of major importance for formation and regulation of the cortical programs for willed motor acts of the animals in the course of acoustic orientation.

[Reactions of neurons of the acoustic area of the cerebellar vermis in cats to binaural presentation of tone signals]. / Reaktsii neironov slukhovoi oblasti chervia mozzhechka koshki na binaural'no pred''iavliaemye tonal'nye signaly.

In anesthetized and immobilized cats, interaural time differences at dichotic stimulation with pure tone were characteristic for maximal activity of each neuron of the cerebellar vermis lobuli VI and VII. The responses of neurons to interaural time differences were the best both at more than 10 dB above the threshold intensity and up to 2.0--2.5 kHz frequency. The maximal change of activity in specific range of time delays when fo above 4 kHz occurred irrespective of the spectrum of tone signal. Two types of neurons were revealed: responding 1) at time delays different from 0, and 2) when time delay was 0. This suggests that each of these types of neurons may play a different part in organization of elements of the localizing behaviour.