Auditory aftereffects of approaching and withdrawing sound sources: Dependence on the trajectory and location of adapting stimuli

Perception of approaching and withdrawing sound sources and their action on auditory aftereffects were studied in the free field. Motion of adapting stimuli was mimicked in two ways: (1) simultaneous opposite changes of amplitude of broadband noise impulses at two loudspeakers placed at 1.1 and 4.5 m from the listener; (2) an increase or a decrease of amplitude of broadband noise impulses in only one loudspeaker, the nearer or the remote one. Motion of test stimuli was mimicked in the former way. Listeners determined direction of the test stimuli motion without any adaptation (control) or after adaptation to stationary, slowly moving (with an amplitude change of 2 dB) and rapidly moving (amplitude change of 12 dB) stimuli. Percentages of “withdrawal” reports were used for construction of psychometric curves. Three phenomena of auditory perception were observed. In the absence of adaptation, a growing-louder effect was revealed, i.e., listeners reported more frequently the test sounds as the approaching ones. Once adapted to stationary or slowly moving stimuli, listeners showed a location-dependent aftereffect. Test stimuli were reported as withdrawing more often as compared with control. The effect was associated with the previous one and was weaker when the distance to the loudspeaker producing adapting stimuli was greater. After adaptation to rapidly moving stimuli, a motion aftereffect was revealed. In this case, listeners reported a direction of test stimuli motion as being opposite to that of adapting stimuli. The motion aftereffect was more pronounced when the adapting stimuli motion was mimicked in the former way, as this method allows estimation of their trajectory. There was no relationship between the motion aftereffect and the growing-louder effect, whichever way the adapting stimuli were produced. There was observed a tendency for reduction of aftereffects of approaching and for intensification of aftereffects of withdrawal with growing distance from source of adapting stimuli.     

Perception of approaching and withdrawing sound sources after exposure to broadband noise: The importance of spatial domain

The existence of space-specific differences in auditory aftereffects has been tested under short-term (5 s) exposure to broadband noise (20–20000 Hz). Adapting stimuli were emitted as constant-amplitude noise sequences. Test stimuli could be of constant and changing amplitude: increasing amplitude of noise pulses in a sequence mimicked an approaching sound source, whereas a decrease in amplitude was perceived as withdrawal. The experiments were done in an anechoic chamber. Auditory aftereffects were assessed under the following conditions: (a) adapting and test stimuli were emitted through a loudspeaker mounted at a distance of 1.1 m from the listener (i.e., subjectively near); (b) both stimuli were emitted from a distance of 4.5 m (subjectively far); (c) adapting and test stimuli were emitted from different distances. The results showed that the characteristics of perception of the imitated sound source motion were similar in proximity and remoteness, which was observed both in the control (without adaptation) and after adaptation to noise. In the absence of adaptation, the psychophysical curves were asymmetrical: the listeners reported approaching of test stimuli more often for both spatial domains. However, the overestimation of test stimuli as drawing closer was more pronounced when they were emitted from the distance of 1.1 m, i.e., from near the listener. After the adaptation to noise, the aftereffects showed spatial specificity and were observed only when adapting and test stimuli belonged to the same spatial domain. These aftereffects were similar in their pattern and strength both in proximity and remoteness: the listeners reported withdrawal of test stimuli more frequently as compared with the control. As a result of these aftereffects, the symmetry of psychometric curves was restored, and the estimation of the direction of sound source motion in the experiment became equiprobable.     

Auditory motion aftereffects of low- and high-frequency sound stimuli

Adaptation of listeners to approaching or receding sound stimuli continued for 5 s under free-field conditions. Motion of the adaptive and test sound stimuli was simulated by means of oppositely directed linear changes in the amplitude of the low- and high-frequency noises (0.05–1 and 3–20 kHz, respectively) from two stationary loudspeakers. In a group of eight subjects with normal hearing, the auditory motion after-effect of the approaching and receding sound stimuli was evaluated by integrated indices that characterized the shift of the psychometric curves in response to the test stimuli under various conditions of listening. The aftereffect occurs in the case when the spectral composition of the adaptive and test stimuli coincides. In response to the high-frequency stimuli, the effect of adaptation to both the approaching and receding sound stimuli was observed, while in response to the low-frequency stimuli, only the approach of stimuli caused an aftereffect. There was no radial motion aftereffect in the case of mismatching the spectral bands of the adaptive and test stimuli. Thus, the frequency selectivity was characteristic of the auditory aftereffect of adaptation to the approaching and receding sound stimuli.     

Auditory motion aftereffects of approaching and withdrawing sound sources

Auditory motion aftereffects of approaching and withdrawing sound sources were investigated in the free field. The approaching and withdrawing of a sound source were simulated by means of differently directed changes in the amplitude of impulses of broadband noise (from 20 Hz to 20 kHz) through two loudspeakers placed 1.1 and 4.5 m away from the listener. Presentation of the adapting approaching and withdrawing stimuli changed the perception of test signals following them: a stationary test signal was perceived by listeners as moving in the direction opposite to one of the movement of the adapting stimulus, whereas a test stimulus slowly moving in same direction as the adapting signal was perceived as stationary. The specific features of the auditory aftereffect of signals moving in a radial direction were similar to those of sound sources moving in a horizontal plane.     

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. 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.     

Changes of evoked potentials caused by sound signals with different localization characteristics

Characteristics of the mismatch negativity (MMN) were studied by presenting the subjects with four blocks of stimuli containing standard series of clicks (90%) simulating a stationery sound image located in the head midline, and one of three different deviant series of clicks (10%) simulating either a stationary sound image located near the left ear or a moving sound image which shifted from the head midline to the left ear or in the opposite direction. All the deviant stimuli elicited the MMN with the minimal peak amplitude and the greatest latency evoked by the deviant series of clicks simulating the sound image moving from the head midline to the left ear. These findings suggest that the MMN may be considered as a pre-perceptual physiological measure of the discrimination accuracy for the sound signals with various spatial locations.     

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 simulated by means of rhythmical noise (from 20 Hz to 20 kHz) impulse sequences with an arising or diminishing amplitude. They were presented to 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 with an adaptation duration of 5 s. At all motion velocities, the aftereffect manifested itself in divergence of psychometric functions upon approaching and withdrawing of adaptors. The direction of function displacements was opposite to that of the adaptor motion. Three parameters reflecting alteration of perception after motion adaptation were determined and compared with control data: the evaluation of stationary test stimuli; the velocity of moving test signal at the point of subjective equality (perceptually unmoving point); and the percentage of responses after averaging over all test signals. These parameters of auditory radial motion aftereffect similarly changed with the adaptor velocity. They demonstrated a significant effect at slow motion (0.68 and 3.43 m/s) and a small effect at a quick motion (6.92 and 9.97 m/s).     

Auditory analysis of the sound source approaching and withdrawing: psychoacoustic and neurophysiological correlates

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.     

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.     

Moving sound source discrimination in humans: Mismatch negativity and psychophysics

The ability to discriminate moving sounds sources with different dynamic properties was studied in humans. Mismatch negativity was studied in an experiment on dichotic stimulation, with deviant stimuli simulating the instantaneous movement of the auditory image to the right or left of the head midline in the horizontal plane. Standard stimuli simulated continuous movement of the sound source to the right or to the left to the same angular distances. It was also established that both deviant stimuli caused mismatch negativity, its parameters being independent on the direction of sound movement. Psychophysical testing of the same group of subjects showed that discrimination between the stimuli was below the psychophysical threshold. The results obtained are discussed from the point of view of current theories of moving sound localization. The correlation between the objective and subjective levels of discrimination of moving auditory images are discussed.     

Quantitative evaluation of tonal sound frequency perception by a man

The possibility of objective purely instrumental investigation of human sensory characteristics in real time is demonstrated by the example of a tonal auditory analyzer. In accordance with our earlier-developed approach, root-mean-square errors of deviations of the tonal sound instantaneous frequency from its mean during vocal reproduction of tonal sounds by probationers, as well as during sound reproduction with the help of a special electronic audio-frequency oscillator, the latter necessitating continuous voluntary control for the desired frequency to be sustained, are chosen as such characteristics. The dependence of the root-mean-square deviation of the reproduced frequency on the mean frequency of the presented tonal sound is found to be virtually linear for both ways of reproduction. The proposed investigation technique can be modified without any radical changes to study the characteristics of human sensory analyzers as regards stimuli of other modalities with a view to assessing the state of the human operator sensory sphere, solving the problems of man-machine interface synthesis and constructing “virtual reality” systems.     

Source localization in underwater sound fields

We investigated the acoustical information present in the field of arbitrary sound sources which may provide direction and distance to the source from a local reading of the sound field parameters. If the effects of reflections are negligible, the particle acceleration is directed radially at the instant of sound pressure nulls. The spectral relation between the radial component of the particle aceleration and the sound pressure is characterized by a critical frequency where a sharp transition occurs in the amplitude ratio and the phase relation of these variables. The critical frequency depends on the distance to the source and depends little on the source type (mono-, di- or quadrupole). Thus, a local reading of the particle acceleration and the sound pressure is in principle sufficient to localize the sound source in three dimensions. Fish might use this kind of information for acoustic orientation.     

Estimation by humans of signals simulating different sound movement directions and specificity of the perception of these signals by patients with temporal epilepsy

The perception of moving sound stimuli that imitate directional sound source movement was studied in healthy subjects and in patients with temporal lobe lesions, as well as in a group of patients with simultaneous lesions of the temporal cortex and hippocampus. Under the conditions of dichotic stimulation of patients with the rightor left-side foci of convulsive activity, the nature and length of the trajectories of the emerging subjective sound images (SSI) were estimated depending on the direction of movement and interaural time difference (700, 400, 200 μs). The audiograms of all patients did not differ from those of healthy subjects, suggesting that the auditory sensitivity of patients remained unimpaired. However, in the patients, the trajectories were shorter than the trajectories in healthy subjects at all the values of the initial time delay and at all the directions of SSI movements. In patients with the cortical temporal epilepsy, changes of the subjective sound field were the most significant in the case of the right-side localization of foci of the convulsive activity. In patients with simultaneous lesions of the temporal cortex and hippocampus, the averaged trajectories of SSI movement differed significantly from those in the group of healthy subjects (p < 0.01) and in patients with a relatively isolated lesion of the temporal cortex (p < 0.05); these trajectories were independent of the initial delay. The mediobasal structures of the temporal lobe that are involved in the epileptic process proved to play a significant role in the perception and estimation of the moving sound stimuli, although they do not belong to the auditory system proper. The possible mechanisms underlying disorders in patients with temporal epilepsy are discussed.     

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° step between the space points with coordinates of elevation from ?45° to 45°. The signals generated on the basis of transfer function sets of 23 subjects were distinguished by regularity and the value of the spectral minimum shift as well as by dynamic changes of the spectral maximum. These dynamic changes were taken into account at creation of “synthetic” signals. In these signals, the vertical movement of sound images in the median plane was simulated either by a consecutive 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.     

Volume-dependent variations of regional lung sound, amplitude, and phase.

Acoustic imaging of the respiratory system demonstrates regional changes of lung sounds that correspond to pulmonary ventilation. We investigated volume-dependent variations of lung sound phase and amplitude between two closely spaced sensors in five adults. Lung sounds were recorded at the posterior right upper, right lower, and left lower lobes during targeted breathing (1.2 +/- 0.2 l/s; volume = 20-50 and 50-80% of vital capacity) and passive sound transmission (< or =0.2 l/s; volumes as above). Average sound amplitudes were obtained after band-pass filtering to 75-150, 150-300, and 300-600 Hz. Cross correlation established the phase relation of sound between sensors. Volume-dependent variations in phase (< or =1.5 ms) and amplitude (< or =11 dB) were observed at the lower lobes in the 150- to 300-Hz band. During inspiration, increasing delay and amplitude of sound at the caudal relative to the cranial sensor were also observed during passive transmission in several subjects. This previously unrecognized behavior of lung sounds over short distances might reflect spatial variations of airways and diaphragms during breathing.     

Evoked potentials of the human cerebral cortex to perceptible and imperceptible sound stimuli

Evoked potentials averaged with the help of an electronic computer (AEP) to brief sound stimuli of subthreshold (3–10 dB below the threshold of the signal's audibility), threshold, and superthreshold (10–60 dB above the threshold) intensity were recorded from the vertex and occipital region of the cranium in healthy people. The dynamics of the changes in the AEP with an increase in the intensity of the sound from subthreshold to superthreshold (60 dB) values was shown. The time and amplitude parameters of AEP to imperceptible and perceptible sound stimuli differed significantly. The most constant, and in many cases the only component of the AEP to an imperceptible stimulus was a long-latent, low-amplitude, slow positive oscillation. The participation of the cerebral cortex in the neural mechanisms of reactions to imperceptible sound stimuli is discussed.V. P. Serbskii Central Scientific-Research Institute of Forensic Psychiatry, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 2, pp. 115–122, March–April, 1971.     

Effects of Acoustic Context on the Perceptual Differences between Spatial Sound Stimuli

We studied the effects of the acoustic context on active and passive discrimination of moving sound signals. Different contexts were created by reversing the role of standard and deviant stimuli in the oddball blocks, while their acoustical features were kept the same. Three types of sounds were used as standard or deviant stimuli in different blocks: stationary midline noises and two (smooth and abrupt) moving sounds moving to the left or right of the midline. Auditory event-related potentials (ERPs) were recorded during passive listening (the sound stimulation ignored), and mismatch negativity potentials (MMNs) were obtained. Active discrimination of sound movements was measured by the hit rate (percent correct responses) and false alarm rate, as well as the reaction time. The influence of the stimulus context on active and passive discrimination of the moving sound stimuli was reflected in the phenomenon known as the effect of deviance direction. The hit rate and MMN amplitude were higher when the deviant moved faster than the standard. The MMN amplitude was more responsive to the velocity of sound stimuli than the hit rate and false alarm rate. The psychophysical measurements in the reversed contexts suggest that smooth and abrupt sound movements may belong to the same perceptual category (moving sounds), while the stationary stimuli form another perceptual category.     

The release of attack and escape behavior by vibratory stimuli in a wandering spider (Cupiennim salei keys.)

Summary The wandering spiderCupiennius salei responds to vibration of the substrate either with predatory behavior (approach) or with a startle reaction or escape behavior (withdrawal) (Fig. 3). The effects of different parameters of the signal in releasing this behavior were studied by applying various artificial stimuli to a spider standing on a vibrating platform with one or more legs. Receptors sensitive to substrate vibration and the trichobothria, which respond to airborne vibration, together determine the response. Spiders without trichobothria: The type of response to vertical vibrations isfrequency-dependent (Fig. 4a), with predatory reactions predominant at low frequencies (3–4 Hz), and withdrawal reactions at high frequencies (350–460 Hz). Whereas approach is most likely to occur at an intermediate, frequency-dependentamplitude, the probability of withdrawal increases continuously with increasing amplitude (Fig. 6). With sine wave stimuli the lowest threshold amplitude for approach is 9 m peak-to-peak (550 Hz, range tested 1–550 Hz) whereas that for withdrawal is 17 m (800 Hz, range tested 1–800 Hz). The threshold for approach is lower by 6–8 dB whenband-limited noise is used, and the probability of an approach response increases as the bandwidth is expanded. The threshold curve for withdrawal, however, is the same in all cases (Fig. 4b and 5). The spider is capable of both frequency and amplitude discrimination.The metatarsal and pretarsal slit sense organs contribute to these responses as is shown by increased thresholds following their destruction (Fig- 7). Intact animals, with functional trichobothria as well as slit sense organs: They have lower thresholds for withdrawal (by ca. 10 dB; Fig. 9) and shorter reaction times than do spiders without trichobothria. Unlike animals without trichobothria the amplitude thresholds of intact animals to bandlimited noise are ca. 7.5 dB lower than those to sine wave stimuli. The approach threshold is the same as that of spiders without trichobothria. According to direct observation the trichobothria are deflected by airborne sound generated by the substrate motion; the deflection angle increases with both amplitude and frequency of substrate vibration (Fig. 10).There is acentral nervous interaction between the signals from the trichobothria and the slit sense organs with the following basic properties: when both of the two receptor systems receive either a prey-like stimulus or a stimulus eliciting withdrawal their effects add, but when the trichobothria receive stimuli unlike prey they inhibit the approach reaction that would otherwise be triggered by substrate vibration.     

Forecast ability of the auditory system during perception of gradually or abruptly moving short sound images

The ability to localize endpoints of sound image trajectories was studied in comparison with stationary sound image positions. Sound images moved either gradually or abruptly to the left or right from the head midline. Different types of sound image movement were simulated by manipulating the interaural time delay. Subjects were asked to estimate the position of the virtual sound source, using the graphic tablet. It was revealed that the perceived endpoints of the moving sound image trajectories, like stationary stimulus positions, depended on the interaural time delay. The perceived endpoints of the moving sound images simulated by stimuli with the final interaural time delay lower than 200 micros were displaced further from the head midline as compared to stationary stimuli of the same interaural time delays. This forward displacement of the perceived position of the moving target can be considered as "representational momentum" and can be explained by mental extrapolation of the dynamic information, which is necessary for successive sensorimotor coordination. For interaural time delays above 400 micros, final positions of gradually and abruptly moving sound sources were closer to the head midline than corresponding stationary sound image position. When comparing the results of both duration conditions, it was shown that in case of longer stimuli the endpoints of gradually moving sound images were lateralized further from the head midline for interaural time delays above 400 micros.     

The role of the medial septum in the acoustic trachea of the cricket Gryllus bimaculatus

The auditory organs of the cricket which are situated in the front legs are joined together by a large transverse trachea which decisively influences their directional characteristics. The transverse trachea is medially divided by a septum. The importance of this septum for the localization of a sound source was tested by means of behavioural experiments in which the phonotactic movements of intact Gryllus bimaculatus females were compared quantitatively with those of the same specimen after perforation of the septum. The septal perforation does not noticeably influence locomotion in the absence of acoustic stimuli but selectively changes essential characteristics of phono taxis: 1) The animals walk in less straight lines. The oscillations around the mean course, typical of phonotaxis, are increased in amplitude, while the frequency decreases. 2) Course deviations from the direction of the sound source become more pronounced. 3) The threshold for phonotaxis is raised by about 10 dB. 4) Both the speed at which the animals walk and the proportion of time during which they are mobile are reduced. The results are discussed in relation to the role of the septum in the mechanism of sound localization, and with regard to its possible importance for the recognition of acoustic patterns.