[The psychoacoustic phenomenon of masking level differences in the human subject studied by auditory evoked potentials]. / Issledovanie psikhoakusticheskogo fenomena "razlichie v urovniakh maskirovki" u cheloveka po slukhovym vyzvannym potentsialam.

Auditory brainstem responses (ABRs), middle latency responses (MLRs), and slow cortical potentials (SCPs) were recorded in normal-hearing adults to trains of low-frequency acoustic signals delivered binaurally against a background of a continuous masking noise. Two stimulus conditions, labelled as binaural homophasic and binaural antiphasic paradigms, respectively, were systematically compared. In the homophasic paradigm both the signals and the masker were in-phase at two ears. In the antiphasic paradigm the signals were 180 degrees out-of-phase at two ears, while the masker was in-phase. The psychoacoustic release from masking in the antiphasic vs. the homophasic paradigm was regularly accompanied by an increase in amplitudes and a shortening in peak latencies of the SCPs. In contrast, no differences were evidenced between the homophasic and the antiphasic paradigms with respect to the ABRs and the MLRs. Considering the generation loci of the studied electric responses, it is concluded that the binaural psychoacoustic phenomenon, referred to as the masking level difference, is operated primarily at the cortical level.

[Age and changes in the latent periods of the slow human auditory potential]. / Vozrastnye izmeneniia latentnykh periodov medlennogo slukhovogo vyzvannogo potentiala cheloveka

Regular changes in latencies of slow auditory evoked potentials were found with age. In particular, peak-latencies of comparatively early deflections, i.e. P1, N1 and P2, progressively diminished. The shortening of latencies was 50-60 ms for the age between 3-7, 8-13, and 25-35 msec further on. The latencies of the later waves, namely P3, N3 and P4, increased by 35-65 ms for the age between 3-7 and 8-13. After these ages, the latency of deflection P3 did not change, while deflections N3 and P4 disappeared. Of all the evoked potential components deflection N2 was the most stable, its latency negligibly shortened with age. In children aged 3-7 two complexes of waves (P1N1P2 and P2N2P3) often overlapped, forming a broad nondifferentiated deflection. The division of the latter was completed at the age of about 8. Long-term developmental changes in wave-shape and parameters of the slow evoked potentials are considered as supporting their mainly nonspecific (extralemniscal) orgin. Basing on correlation revealed between the late evoked potential components and EEG synchronization level, a hypothesis is advanced according to which these components are generated with participation of the nonspecific synchronizing system.