[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.

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 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.

[Role of phasic changes in sound signal in localization of auditory image].

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.

[Evoked potentials of the cat inferior colliculus to acoustic stimuli simulating sound source movement with different velocities in opposite directions].

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.

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.

[Comparison of binaural release from forward masking in animals and humans. Electrophysiologic study].

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.

[Neuronal reactions of the fastigial nucleus in the cat to sound signals].

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.

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.

[Selectivity of trace reactions of medial geniculate neurons to the rate of simulated movement of a sound source in the cat].

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.

[Response of medial geniculate body responses to the velocity of simulated sound source movement in the cat].

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.

[Characteristics of cat sensomotor cortex neuron responses to monaural and binaural stimulation].

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.

[Reactions of neurons of the acoustic area of the cerebellar vermis in cats to binaural presentation of tone signals].

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.