The time scale of adaptation in tonal sequence processing by the mouse auditory midbrain neurons.

The time course of poststimulatory adaptation of the inferior colliculus central nucleus (ICC) of CBB6F1 hybrid mice to sound sequences, specifically, series of four tonal stimuli presented at intervals of 0, 2, 4, 10, 20, 50, 100, 200, 500, 700, 1000, and 1500 ms were studied. Assessment of the adaptation of the entire neuronal population have shown that, at an interstimulus interval of 0-200 ms, the response to the first tone in a series is significantly stronger than those to the second to fourth tones, the strengths of the latter three responses not differing significantly from one another. If the interstimulus interval is 500 ms or longer, the response to none of the tones in a series differs significantly in strength from the others. The role of adaptation of midbrain neurons to the grouping of components of bioacoustic stimuli is discussed.

[NEUROPHYSIOLOGIC APPROACHES TO THE STUDY OF FUNCTIONAL ROLE OF THE AUDITORY CRITICAL BANDS].

Neurophysiologic data on participation of the critical band mechanism in sound localization and recognition are presented. Single unit activity was recorded extracellularly-in the central nucleus of inferior colliculus of the house mouse females. First, we studied sensitivity of neurons to acoustic signals simulating spectral localization cues (notch noise with different bandwidths). Comparison of neuron responses depending on notch bandwidths revealed that 1/3 octave notch bandwidths was optimal for the analysis of the localization-significant spectral information. This notch bandwidths corresponded to the critical bandwidths of the auditory midbrain neurons evaluated earlier by the simultaneous masking paradigm. Second, we studied selectivity of neuronal responses to the mouse pups' wriggling call, a set of its models and frequency components. The data obtained showed that models of wriggling call frequency components, located as in natural call, in three non-overlapping critical bands produced stronger neuronal responses than other models. We assume that our finding proves the universal role of the critical bands mechanism in processing different parameters of acoustic stimuli. Key words: inferior colliculus, auditory critical bands, sound source localization, analysis of bioacoustic signals.

[Perception of approaching and withdrawing sound sources following exposure to broadband noise. The effect of spatial domain].

The spatial specificity of auditory aftereffect was studied after a short-time adaptation (5 s) to the broadband noise (20-20000 Hz). Adapting stimuli were sequences of noise impulses with the constant amplitude, test stimuli--with the constant and changing amplitude: an increase of amplitude of impulses in sequence was perceived by listeners as approach of the sound source, while a decrease of amplitude--as its withdrawal. The experiments were performed in an anechoic chamber. The auditory aftereffect was estimated under the following conditions: the adapting and test stimuli were presented from the loudspeaker located at a distance of 1.1 m from the listeners (the subjectively near spatial domain) or 4.5 m from the listeners (the subjectively near spatial domain) or 4.5 m from the listeners (the subjectively far spatial domain); the adapting and test stimuli were presented from different distances. The obtained data showed that perception of the imitated movement of the sound source in both spatial domains had the common characteristic peculiarities that manifested themselves both under control conditions without adaptation and after adaptation to noise. In the absence of adaptation for both distances, an asymmetry of psychophysical curves was observed: the listeners estimated the test stimuli more often as approaching. The overestimation by listeners of test stimuli as the approaching ones was more pronounced at their presentation from the distance of 1.1 m, i. e., from the subjectively near spatial domain. After adaptation to noise the aftereffects showed spatial specificity in both spatial domains: they were observed only at the spatial coincidence of adapting and test stimuli and were absent at their separation. The aftereffects observed in two spatial domains were similar in direction and value: the listeners estimated the test stimuli more often as withdrawing as compared to control. The result of such aftereffect was restoration of the symmetry of psychometric curves and of the equiprobable estimation of direction of movement of test signals.

[Asymmetry and spatial specificity of auditory aftereffects following adaptation to signals simulating approach and withdrawal of sound sources].

The spatial specificity of auditory approaching and withdrawing aftereffects was investigated in an anechoic chamber. The adapting and testing stimuli were presented from loudspeakers located in front of the subject at the distance of 1.1 m (near) and 4.5 m (far) from the listener's head. Approach and withdrawal of stimuli were simulated by increasing or decreasing the amplitude of the wide-noise impulse sequence. The listeners were required to determine the movement direction of test stimulus following each 5-s adaptation period. The listeners' "withdrawal" responses were used for psychometric functions plotting and for quantitative assessment of auditory aftereffect. The data summarized for all 8 participants indicated that the asymmetry of approaching and withdrawing aftereffects depended on spatial localization of adaptor and test. The asymmetry of aftereffects was largest when adaptor and test were presented from the same loudspeaker (either near or far). Adaptation to the approach induced a directionally dependent displacement of the psychometric functions relative to control condition without adaptation and adaptation to the withdrawal was not. The magnitude of approaching aftereffect was greater when adaptor and test were located in near spatial domain than when they came from far domain. When adaptor and test were presented from the distinct loudspeakers, magnitude approaching aftereffect was decreasing in comparison to the same spatial localization, but after adaptation to withdrawal it was increasing. As a result, the directionally dependent displacements of the psychometric functions relative to control condition were observed after adaptation as to approach and to withdrawal. The discrepancy of the psychometric functions received after adaptation to approach and to withdrawal at near and far spatial domains was greater under the same localization of adaptor and test in comparison to their distinct localization. We assume that the peculiarities of approaching and withdrawing aftereffects observed reflect their spatial specificity. It is possible that spatial peculiarities of approaching and withdrawing aftereffects can be associated with specialized mechanisms for analysis of motion at the different distance from subject.

[Auditory aftereffects with approaching and withdrawing sound sources: dependence on trajectory and domain of presentation of adapting stimuli].

The perceptual peculiarities of sound source withdrawing and approaching and their influence on auditory aftereffects were studied in the free field. The radial movement of the auditory adapting stimuli was imitated by two methods: (1) by oppositely directed simultaneous amplitude change of the wideband signals at two loudspeakers placed at 1.1 and 4.5 m from a listener; (2) by an increase or a decrease of the wideband noise amplitude of the impulses at one of the loudspeakers--whether close or distant. The radial auditory movement of test stimuli was imitated by using the first method of imitation of adapting stimuli movement. Nine listeners estimated the direction of test stimuli movement without adaptation (control) and after adaptation. Adapting stimuli were stationary, slowly moving with sound level variation of 2 dB and rapidly moving with variation of 12 dB. The percentage of "withdrawing" responses was used for psychometric curve construction. Three perceptual phenomena were found. The growing louder effect was shown in control series without adaptation. The effect was characterized by a decrease of the number of "withdrawing" responses and overestimation of test stimuli as approaching. The position-dependent aftereffects were noticed after adaptation to the stationary and slowly moving sound stimuli. The aftereffect was manifested as an increase of the number of "withdrawing" responses and overestimation of test stimuli as withdrawal. The effect was reduced with increase of the distance between the listener and the loudspeaker. Movement aftereffects were revealed after adaptation to the rapidly moving stimuli. Aftereffects were direction-dependent: the number of "withdrawal" responses after adaptation to approach increased, whereas after adaptation to withdrawal it decreased relative to control. The movement aftereffects were more pronounced at imitation of movement of adapting stimuli by the first method. In this case the listener could determine the starting and the finishing points of movement trajectory. Interaction of movement aftereffects with the growing louder effect was absent in all ways of presentation of adapting stimuli. With increase of distance to the source of adapting stimuli, there was observed a tendency for a decrease of aftereffect of approach and for an increase of aftereffect of withdrawal.

[The auditory aftereffects of radial sound source motion with different velocities].

Auditory aftereffects were evaluated after short adaptation to radial sound source motion with different velocities. Approach and withdrawal of the sound source were imitated by means of rhythmical noise (20 Hz-20 kHz) impulse sequences with arising or diminishing amplitude. They were presented in an anechoic chamber through two loudspeakers placed at 1.1 and 4.5 m from the listener. The adapting stimulus velocities were 0.68, 3.43, 6.92 and 9.97 m/s at adaptation duration of 5 s. By every adaptor speed an aftereffect revealed as distinguishing of psychometric function at approaching and withdrawing adaptors. The direction of function displacements was opposite to one of adaptor motion. Three parameters reflecting alteration of perception after motion adaptation were determined and were compared with control data: an evaluation of stationary test stimuli; a velocity of moving test signal at the point of subjective equality (perceptually unmoving point); a percentage of responses after averaging across all test signals. These parameters of auditory radial motion aftereffect have similar tendencies to change with adaptor velocity. They have demonstrated significant effect at slow motion (0.68 and 3.43 m/s) and small effect at quick motion (6.92 and 9.97 m/s).

[Auditory motion aftereffects with approaching and withdrawing sound sources].

Auditory motion aftereffects with approaching and withdrawing sound sources were investigated in the free field. Radial sound moving image (approaching or withdrawing) was imitated by means of rhythmical noise impulse sequences with arising or diminishing amplitude presented through two loudspeakers placed at 1.1 and 4.5 m from the listener. The adaptation to the auditory approaching and withdrawing exposure caused changing of evaluation by listeners the test signals followed by adapting ones. Stationary test signals were perceived by listeners as moving to the direction opposite to ones presented during adaptation. Stimuli subtly moving to the adapting signals' direction were determined as stationary. The peculiarities of auditory motion aftereffects with approaching and withdrawing sound sources were similar to ones with horizontally moving sound sources.

[Localization of virtual stimuli moving in the median plane by listeners of different age].

Capability for identification of direction of movement of sound images (upward or downward) was studied in listeners of two age groups: 19- 27-year-old (11 subjects) and 55- 73-year-old (9 subjects). Various sound models of movement in the median plane were used as stimuli. Initially, a model of movement was developed based on filtration of broadband noise pulses by sets of non-individualized. i. e., measured in other listeners, head-related transfer functions. These functions corresponded to consecutive positions of the sound sources with the 5.6 degrees step between the space points with coordinates of elevation from -45 degrees to 45 degrees. The signals generated on the basis of transfer function sets of 23 subjects were distinguished by regulatory and value of the spectral minimum shift as well as by dynamic changes of the spectral maximum. Then the dynamic changes typical on non-individual sound images were used to create synthetic models. In these models, movement of sound images in the median plane was simulated either by a regular shift of the spectral minimum in broadband noise pulses or by a combination of the spectral minimum shift with a simultaneous change of the spectral maximum width and power. The obtained data have shown that young listeners with the high capability for vertical localization could identify direction of the sound image movement based on displacement of the spectral minimum in the broadband noise. For identification of direction of the sound image movement, the younger listeners with poor capabilities for vertical localization and the older listeners used dynamic changes of the signal power, which were connected mainly with the spectral maximum range.

[Tendencies in auditory physiology].

Main tendencies in studying of human and animals auditory system with psychoacoustical and electrophysiologycal methods are considered. Concerning psychoacoustical studies some basic data are presented as well as contemporary tendencies in hearing physiology in analysis of the intensity, frequency, temporal characteristics of the sound signals and data related to such phenomena as masking and adaptation. Data concerning directional hearing are presented in detail as a basis of auditory virtual reality. In electrophysiological studies of the auditory system detailed analysis of mapping in auditory centers and mechanisms concerning localization of unmoved and moving auditory stimuli was performed. Special attempt was paid to consider the reflection of different types of auditory signals in human evoked potentials.

Changes in the latency of mouse inferior colliculus neuron responses depending on the position and direction of movement of spectral contrast.

Changes in the latency of mouse (Mus musculus) inferior colliculus neuron responses in the presence of wideband sound signals with spectral notches and noise bands with regularly varying central notch/band frequencies were studied. Relationships between the latency and the magnitude of the response on the one hand and the central notch/band frequency on the other were obtained (latency and spike count functions). Crossing of the margins of the excitatory areas of the responses of the frequency receptive fields of neurons by spectral notches/noise bands could lead to displacement of latency functions (and corresponding displacements in spike count functions). Direction-dependent shifts in latency and spike count functions were more characteristic of primary-like and V-shaped neurons. The most interesting feature of the directional sensitivity of inhibition-dependent neurons was the selective decrease in the latency and selective synchronization of the initial spike response (with a corresponding increase in the spike count). The dynamic properties of inhibition-dependent neurons can be explained on the basis of their selective sensitivity to the position of the spectral contrast in the frequency receptive field, which is associated with disinhibition, and by the nature of the distribution of the excitatory and inhibitory inputs. The extents of these effects depended on the spectral shape of the signals and the widths of the spectral notches.

[Changes in response latencies of the mouse inferior colliculus neurons depending on the position and movement direction of the spectral contrast]. / Izmeneniia latentnosti otvetov zadnego kholma myshi v zavisimosti ot polozheniia i napravleniia peremeshcheniia spektral'nogo kontrasta.

Variability of response latency of neurons in the mouse inferior colliculus of (Mus musculus) to signals of notch noise and of noise band with regular varying of the notch/band center frequencies, have been studied. Plots of latency and spike count versus notch/band center frequency were constructed (latency functions and spike count functions). Spectral notch/noise band motion crossing boundaries of excitatory areas in the neurons frequency receptive field could produce latency function shifts (and appropriate to this spike count function shifts). Direction-dependent latency function and spike count function shifts were mostly seen for primary-like and V-shape neurons. The most interesting feature of directional sensitivity of inhibitory-dominated neurons was the selective shortening of latency and selective synchronization of the initial spikes (with appropriate to this spike count rise). The dynamic properties of inhibitory-dominated neurons can be explained on the basis of their selective sensitivity to position of spectral contrast in frequency receptive field, connected with disinhibition, and of the character of distribution of excitatory and inhibitory inputs. Manifestation of motion effects was influenced by spectral shape of noise signal and notch width.

The selectivity of neurons in the auditory zone of the mouse midbrain to the direction of movement of a spectral notch in wide-band noise.

A series of noise signals was synthesized with spectral notches whose central frequencies moved regularly along the frequency range (from low frequencies to high and from high frequencies to low), imitating movement of the sound source in the vertical plane. The spike responses of neurons in the inferior colliculus of the mouse (Mus musculus) to noise signals changed as the spectral notch moved relative to the excitatory and inhibitory areas of the receptive fields of the neurons and depended on the notch width. Disinhibition reactions in the inhibitory zones were more marked when a frequency notch in the inhibitory zone was followed by a frequency notch in the excitatory part of the response. It is suggested that the selectivity of neurons to the direction of movement of the spectral notch in a noise signal is based on the interaction of the excitatory and inhibitory inputs. The overall set of neuron responses can provide information on the movement of the sound source in acoustic space.

Activity of neurons in the mouse inferior colliculus in relation to the position and direction of displacement of spectral contrast.

The variability of the responses of neurons in the inferior colliculus of the mouse (Mus musculus) to sequences of signals of noise bands and wide-band noise with spectral notches with regular changes (by 1/12 octave) in the central band frequency or notch frequency was studied. When the width of spectral changes was 1/3 octave, neurons with strong inhibitory influences in the excitatory zone of the response ("inhibition-dependent" neurons) showed low levels of spike activity if the noise band completely covered the excitatory part of the response. The most effective stimuli for these neurons were spectral contrasts passing through the center of the excitatory part of the response (through or close to the characteristic frequency). The responses of neurons to spectral contrasts created by noise bands and noises with notches were identical. It is suggested that approximation of the inhibitory and excitatory inputs sharpens the frequency tuning of neurons to the position of the spectral contrasts, as occurs in the visual system. The selectivity of neurons to the direction of moving spectral contrasts is manifest as a difference in responses when they move from the excitatory area of the response to the inhibitory and vice versa. The functional significance of the contrast mechanism for the analysis of sound source movement based on direction-dependent spectral features associated with the transfer characteristics of the external ear is discussed.

[Dependence of the mouse inferior colliculus neurons activity on position and direction of movement of the spectral contrast]. / Aktivnost' neironov zadnego kholma myshi v zavisimosti ot polozheniia i napravleniia peremeshcheniia spektral'nogo kontrasta.

Response variability of the single neurons of the inferior colliculus of mouse (Mus musculus) to series of noise bands and of notch noises with regular 1/12 octave steps of the band/notch center frequency and width of noise band/notch 1/3 octave, was studied. Neurons with strong inhibitory influence in excitatory response area (inhibitory-dominated) show low impulse activity when noise band exceeded excitatory response area. Spectral contrasts crossing the center of excitatory response area (at CF or nearly CF) were found to be the most efficient stimuli for such neurons. Neuron responses to spectral contrasts derived both from noise band and noise notch were identical. Approaching of inhibitory and excitatory inputs is expected to sharpen the auditory neurons frequency tuning to position of spectral contrasts, similar to neuronal processing in visual system. Neuron selectivity to the direction of spectral contrasts movement was determined in neuron response differences when the noise band or notch shifted from excitatory area to inhibitory areas as compared with shift in the opposite direction. Functional role of contrast mechanism for sound localization on the base spectral cues related to external ear transfer characteristics is discussed.

[Sensitivity of the neurons in the auditory inferior colliculus of mice to the direction of the shift of broadband spectral notch noise]. / Izbiratel'nost' neironov slukhovogo otdela srednego mozga myshi k napravleniiu peremeshcheniia spektral'nykh vyrezok v shirokopolostnom shume.

Series of a notch noise with regular shifts of the notch center frequency: one--from low frequencies to high frequencies and the other--from high frequencies to the low, were synthesized. The notch noise series imitated sound source vertical moving. Single neuron's responses of inferior colliculus of the house mouse (Mus musculus) to the notch-noises altered with notch central frequency varying through excitatory and inhibitory frequency response areas in neurones' receptive fields. The neural responses alteration to the notch noise varying depended on the bandwidth of notch. Disinhibition in inhibitory side band could be higher if the notch overlying the inhibitory areas followed the notch overlying the excitatory areas. The data obtained make it possible to consider the excitatory and inhibitory interaction as a mechanism of neural sensitivity to the notch moving direction. Neurones' response set could provide information about sound source moving over auditory space.

[Auditory analysis of the sound source approaching and withdrawing: psychoacoustic and neurophysiological correlates]. / Slukhovaia otsenka priblizheniia i udaleniia istochnika zvuka: psikhoakusticheskie i élektrofizicheskie korreliaty.

The findings seemed to be based on direction and velocity of modelling the radial sound source shifting in free acoustic field. The threshold and the optimal parameters of the acoustic model imitating the approaching and withdrawing of the sound source shifting in silence and under conditions of noise, were established. A correlation between peak-to-peak amplitudes of the N1-P2 components of auditory EPs and the imitated direction of the sound shifting, was shown. The role of different left and right hemispheres' areas in perception of the radial sound source was analysed. The detector features of the central auditory neurones were shown as a possible mechanism of estimating the sound source approaching and withdrawal.