[Mismatch negativity in the auditory event-related potentials in response to abrupt and smooth displacements of virtual sound source].

The work investigated event-related potentials, mismatch negativity (MMN), and P3a component under dichotic stimulation with deviant stimuli simulating abrupt or smooth displacement of auditory images to the left or to the right from the head midline by means of interaural time delay introduced into the deviant stimuli. Repetitive standard stimuli were localized near the head midline. All deviant stimuli elicited mismatch negativity and P3a component. It was shown the MMN for smooth deviant motion was lower than that for the abrupt deviant displacement. MMN amplitude for both deviant types obviously depended on interaural time delay, which confirms that MMN might be considered as a measure of the auditory system spatial discriminative ability. The P3a component demonstrated the same amplitude dependences as the MMN. The results obtained are discussed in respect to manifestation of the processes underlying the auditory motion detection in the event-related potentials.

[Perception of short musical fragments by hypomaniac patients].

Emotional assessment of short fragments from pieces of chamber music was studied in patients in steady elated mood (hypomaniac). Six fragments, assessed by healthy subjects as emotionally positive, neutral or negative were used. The examined subjects were shown to be capable for an emotional assessment of the musical fragments. The most pronounced difference of the examined patients from healthy subjects and depressive patients examined earlier was the predominance of neutral assessments in hypomaniacs.

[Auditory event-related potentials to the apparent auditory image motion].

Auditory event-related potentials (ERP) were registered to the dichotically presented white noise stimuli (duration 1500 ms, band 150-1200 Hz). Abrupt or gradual change ofinteraural time difference in the middle of stimuli (750 ms after sound offset) was perceived as an apparent auditory image (AI) instant relocation or motion from the midline to one of the ears. In responses these stimuli two ERPs were observed: one to the sound onset, and second--to the onset of motion or AI relocation. ERPs to AI relocation differed from those to sound onset in longer components latencies (123 ms versus 105 ms for N 1,227 ms versus 190 ms for P2). In responses to AI motion component latencies were even longer (N1: 137 ms, P2: 240 ms); N1 amplitude was greater at sites contralateral to the AI motion direction.

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.

[Responses of neurons in the primary auditory cortex of the cat to the auditory motion stimuli with variable interaural delay]. / Reaktsiia neironov pervichnoy slukhovoi kory koshki na dvizhushcheisia stimul s dinamicheski izmeniaiushcheisia mezhushnoi zaderzhkoy.

Unit responses in the primary auditory cortex of anesthetized cats to stationary and apparently moving stimuli resulted from a static and dynamically varying interaural delay (ITD) were recorded. The static stimuli consisted of binaurally presented tones and clicks. The dynamic stimuli were produced by in-phase and out-of-phase binaurally presented click trains with time-varying ITD. Sensitivity to ITDs was mostly seen in responses of the neurons with low characteristic frequency (below 2.8 kHz). All cells sampled with static stimuli responded to simulated motion. A motion effect could take the form of a difference in response magnitude depending on the direction of stimulus motion and a shift in the ITD-function opposite the direction of motion. The magnitude of motion effects was influenced by the position of motion trajectory relative to the ITD-function. The greatest motion effect was produced by motion crossing the ITD-function slopes.

[Brain activity induced by changes in acoustic stimuli]. / Mozgovaia aktivnost', vyzvannaia izmeneniiami slukhovykh stimulov.

The averaged variants of the EPs to deviant stimuli had more obvious components N100, N250 and P300 as compared with the EPs to standard stimuli. The data obtained show occurrence of a negative shift during presentation of a rare stimulus within the sequence of standard ones. This negativity seems to reflect the processes of comparison of acting excitations with the traces of previous stimuli.