Forward masking in the evoked responses of the guinea pig auditory cortex: effects of variation of the interaural time and phase differences

In anaesthesized guinea pigs the evoked potentials of the auditory cortex were studied in a forward masking paradigm. In-phase and out-of-phase binaurally presented clicks with interaural time delay (ITD) were used as masker, in-phase click with ITD = 0 served as probe signal. Addition of the masking stimulus suppressed the probe-evoked response that followed the masker. The magnitude of the suppression correlated with the amount of the masker-evoked response: an increase in masker-evoked excitation caused a greater reduction in probe response magnitude. Amplitude of masker-evoked response was seen to be a monotonic or non-monotonic function of ITD. The non-monotonic response exhibited a sensitivity to the interaural phase differences when in-phase and out-of-phase maskers were presented, and showed the tendency to be periodic function of ITD in the expanded range of ITD values. Phase-sensitive responses differed in recovery time following the in-phase and out-of-phase masking stimuli. At near-threshold levels of a forward masker an enhancement of the probe-evoked response was observed.     

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.     

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.     

Effects of binaural decorrelation on neural and behavioral processing of interaural level differences in the barn owl (Tyto alba)

The effect of binaural decorrelation on the processing of interaural level difference cues in the barn owl (Tyto alba) was examined behaviorally and electrophysiologically. The electrophysiology experiment measured the effect of variations in binaural correlation on the first stage of interaural level difference encoding in the central nervous system. The responses of single neurons in the posterior part of the ventral nucleus of the lateral lemniscus were recorded to stimulation with binaurally correlated and binaurally uncorrelated noise. No significant differences in interaural level difference sensitivity were found between conditions. Neurons in the posterior part of the ventral nucleus of the lateral lemniscus encode the interaural level difference of binaurally correlated and binaurally uncorrelated noise with equal accuracy and precision. This nucleus therefore supplies higher auditory centers with an undegraded interaural level difference signal for sound stimuli that lack a coherent interaural time difference. The behavioral experiment measured auditory saccades in response to interaural level differences presented in binaurally correlated and binaurally uncorrelated noise. The precision and accuracy of sound localization based on interaural level difference was reduced but not eliminated for binaurally uncorrelated signals. The observation that barn owls continue to vary auditory saccades with the interaural level difference of binaurally uncorrelated stimuli suggests that neurons that drive head saccades can be activated by incomplete auditory spatial information.     

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).     

Influence of Visual Motion,Suggestion, and Illusory Motion on Self-Motion Perception in the Horizontal Plane

A moving visual field can induce the feeling of self-motion or vection. Illusory motion from static repeated asymmetric patterns creates a compelling visual motion stimulus, but it is unclear if such illusory motion can induce a feeling of self-motion or alter self-motion perception. In these experiments, human subjects reported the perceived direction of self-motion for sway translation and yaw rotation at the end of a period of viewing set visual stimuli coordinated with varying inertial stimuli. This tested the hypothesis that illusory visual motion would influence self-motion perception in the horizontal plane. Trials were arranged into 5 blocks based on stimulus type: moving star field with yaw rotation, moving star field with sway translation, illusory motion with yaw, illusory motion with sway, and static arrows with sway. Static arrows were used to evaluate the effect of cognitive suggestion on self-motion perception. Each trial had a control condition; the illusory motion controls were altered versions of the experimental image, which removed the illusory motion effect. For the moving visual stimulus, controls were carried out in a dark room. With the arrow visual stimulus, controls were a gray screen. In blocks containing a visual stimulus there was an 8s viewing interval with the inertial stimulus occurring over the final 1s. This allowed measurement of the visual illusion perception using objective methods. When no visual stimulus was present, only the 1s motion stimulus was presented. Eight women and five men (mean age 37) participated. To assess for a shift in self-motion perception, the effect of each visual stimulus on the self-motion stimulus (cm/s) at which subjects were equally likely to report motion in either direction was measured. Significant effects were seen for moving star fields for both translation (p = 0.001) and rotation (p<0.001), and arrows (p = 0.02). For the visual motion stimuli, inertial motion perception was shifted in the direction consistent with the visual stimulus. Arrows had a small effect on self-motion perception driven by a minority of subjects. There was no significant effect of illusory motion on self-motion perception for either translation or rotation (p>0.1 for both). Thus, although a true moving visual field can induce self-motion, results of this study show that illusory motion does not.     

Human Vection Perception Using Inertial Nulling and Certainty Estimation: The Effect of Migraine History

Vection is an illusory perception of self-motion that can occur when visual motion fills the majority of the visual field. This study examines the effect of the duration of visual field movement (VFM) on the perceived strength of self-motion using an inertial nulling (IN) and a magnitude estimation technique based on the certainty that motion occurred (certainty estimation, CE). These techniques were then used to investigate the association between migraine diagnosis and the strength of perceived vection. Visual star-field stimuli consistent with either looming or receding motion were presented for 1, 4, 8 or 16s. Subjects reported the perceived direction of self-motion during the final 1s of the stimulus. For the IN method, an inertial nulling motion was delivered during this final 1s of the visual stimulus, and subjects reported the direction of perceived self-motion during this final second. The magnitude of inertial motion was varied adaptively to determine the point of subjective equality (PSE) at which forward or backward responses were equally likely. For the CE trials the same range of VFM was used but without inertial motion and subjects rated their certainty of motion on a scale of 0–100. PSE determined with the IN technique depended on direction and duration of visual motion and the CE technique showed greater certainty of perceived vection with longer VFM duration. A strong correlation between CE and IN techniques was present for the 8s stimulus. There was appreciable between-subject variation in both CE and IN techniques and migraine was associated with significantly increased perception of self-motion by CE and IN at 8 and 16s. Together, these results suggest that vection may be measured by both CE and IN techniques with good correlation. The results also suggest that susceptibility to vection may be higher in subjects with a history of migraine.     

Perceived direction of motion determined by adaptation to static binocular images

In Li and Atick's [1, 2] theory of efficient stereo coding, the two eyes' signals are transformed into uncorrelated binocular summation and difference signals, and gain control is applied to the summation and differencing channels to optimize their sensitivities. In natural vision, the optimal channel sensitivities vary from moment to moment, depending on the strengths of the summation and difference signals; these channels should therefore be separately adaptable, whereby a channel's sensitivity is reduced following overexposure to adaptation stimuli that selectively stimulate that channel. This predicts a remarkable effect of binocular adaptation on perceived direction of a dichoptic motion stimulus [3]. For this stimulus, the summation and difference signals move in opposite directions, so perceived motion direction (upward or downward) should depend on which of the two binocular channels is most strongly adapted, even if the adaptation stimuli are completely static. We confirmed this prediction: a single static dichoptic adaptation stimulus presented for less than 1 s can control perceived direction of a subsequently presented dichoptic motion stimulus. This is not predicted by any current model of motion perception and suggests that the visual cortex quickly adapts to the prevailing binocular image statistics to maximize information-coding efficiency.     

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.     

Response of Neurons of The Inferior Colliculi of Cats To Changes in the Intensity of One of The Monaural Components of Binaurally Presented Stimuli

In spite of the large quantity of psychophysiological investigations of binaural hearing, a systematic study of its concrete mechanisms has only been begun comparatively recently (cf. review [1]). In particular, changes in neuron response under conditions of lateral differentiation brought about by varying the intensity of one of the monaural components of binaurally presented stimuli have been studied in detail only at the site of the superior olivary body (3, 4, 6) — the first section of the auditory system — where afferent fibers from the right and left cochlea converge (7, 9). Published data provide evidence that variations in the intensity of one of the monaural components of binaurally presented signals has an appreciable effect on the firing rate of single neurons of the inferior colli cuius (5, 8), which is situated directly behind the superior olivary body of the auditory system. in the present report, the types of response of neurons in the inferior colliculus to variations in the intensity of one of the monaural components of binaurally presented stimuli are systematically investigated.     

How Moving Backgrounds Influence Interception

Reaching movements towards an object are continuously guided by visual information about the target and the arm. Such guidance increases precision and allows one to adjust the movement if the target unexpectedly moves. On-going arm movements are also influenced by motion in the surrounding. Fast responses to motion in the surrounding could help cope with moving obstacles and with the consequences of changes in one’s eye orientation and vantage point. To further evaluate how motion in the surrounding influences interceptive movements we asked subjects to tap a moving target when it reached a second, static target. We varied the direction and location of motion in the surrounding, as well as details of the stimuli that are known to influence eye movements. Subjects were most sensitive to motion in the background when such motion was near the targets. Whether or not the eyes were moving, and the direction of the background motion in relation to the direction in which the eyes were moving, had very little influence on the response to the background motion. We conclude that the responses to background motion are driven by motion near the target rather than by a global analysis of the optic flow and its relation with other information about self-motion.     

Responses of central auditory neurons to frequency-modulated stimuli

Unit responses of the inferior colliculi of albino rats to frequency-modulated stimuli were investigated. The number of spikes, firing pattern, and duration of the discharge were determined. Parameters of unit responses obtained with different directions of frequency modulation were compared with the results of testing the effect of constant-frequency tones on the neurons. The distinguishing features of the unit responses to stimuli with different directions of frequency modulation were compared with the characteristics of the frequency-threshold curve and the lateral inhibitory zones, taken as indices of the unit responses to constant-frequency tones. With a change in stimulus frequency upward or downward from the initial level the unit responses to both directions could be similar as regards the number of spikes per discharge and the firing pattern or could differ sharply depending on the direction or, finally, they could arise only if the stimulus frequency changed in one direction. In some cases selectivity for the direction of the change in stimulus frequency was due to the width and position of the lateral inhibitory zones. However, for one-third of the neurons tested analysis of the spatial characteristics of the excitatory and inhibitory zones alone was insufficient to explain the high selectivity in the formation of a response to a stimulus with frequency modulation in one direction only.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol.6, No.3, pp.237–245, May–June, 1974.     

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. They averaged as 1.6, 1.5 and 1.4 for the responses of the inferior colliculus, auditory cortex and long latency potentials, resp., at the stimuli intensities of 50-65 dB SPL, and then decreased to zero during the time course of the probe response recovery. Correlation of this parameter with the stimulus intensity was positive.     

Does the magnocellular octaval nucleus process auditory information in the toadfish, Opsanus tau?

Previous work on auditory processing in Opsanus tau has focused on the descending octaval nucleus; however, the magnocellular octaval nucleus receives similar inputs from the otolithic endorgans. The purpose of this study was to assess whether cells in any of the three subdivisions of the magnocellular nucleus respond to auditory frequencies and encode sound source direction. Extracellular recording sites were chosen based on anatomical landmarks, and neurobiotin injections confirmed the location of auditory sites in subdivisions of the magnocellular nucleus. In general, the auditory cells in M2 and M3 responded best to frequencies at or below 100 Hz. Most auditory cells responded well to directional stimuli presented along axes in the horizontal plane. Cells in M3 (not M2) also responded to lateral line stimulation, consistent with otolithic endorgan and lateral line inputs to M3. The convergence of auditory and lateral line inputs in M3, the lack of Mauthner cells in this species, and previous evidence that the magnocellular nucleus does not contribute to ascending auditory pathways suggest to us that the large cells of M3 may play a role in rapid behavioral responses to particle motion stimuli in oyster toadfish.     

The Enhancement of the N1 Wave Elicited by Sensory Stimuli Presented at Very Short Inter-Stimulus Intervals Is a General Feature across Sensory Systems

Background

A paradoxical enhancement of the magnitude of the N1 wave of the auditory event-related potential (ERP) has been described when auditory stimuli are presented at very short (<400 ms) inter-stimulus intervals (ISI). Here, we examined whether this enhancement is specific for the auditory system, or whether it also affects ERPs elicited by stimuli belonging to other sensory modalities.

Methodology and Principal Findings

We recorded ERPs elicited by auditory and somatosensory stimuli in 13 healthy subjects. For each sensory modality, 4800 stimuli were presented. Auditory stimuli consisted in brief tones presented binaurally, and somatosensory stimuli consisted in constant-current electrical pulses applied to the right median nerve. Stimuli were delivered continuously, and the ISI was varied randomly between 100 and 1000 ms. We found that the ISI had a similar effect on both auditory and somatosensory ERPs. In both sensory modalities, ISI had an opposite effect on the magnitude of the N1 and P2 waves: the magnitude of the auditory and the somatosensory N1 was significantly increased at ISI≤200 ms, while the magnitude of the auditory and the somatosensory P2 was significantly decreased at ISI≤200 ms.

Conclusion and Significance

The observation that both the auditory and the somatosensory N1 are enhanced at short ISIs indicates that this phenomenon reflects a physiological property that is common across sensory systems, rather than, as previously suggested, unique for the auditory system. Two of the hypotheses most frequently put forward to explain this observation, namely (i) the decreased contribution of inhibitory postsynaptic potentials to the recorded scalp ERPs and (ii) the decreased contribution of ‘latent inhibition’, are discussed. Because neither of these two hypotheses can satisfactorily account for the concomitant reduction of the auditory and the somatosensory P2, we propose a third, novel hypothesis, consisting in the modulation of a single neural component contributing to both the N1 and the P2 waves.     

Effects of Near-Threshold Stimulation of the Vestibular Apparatus on Postural Responses Evoked by Displacements of the Visualized Surrounding

In healthy subjects in the relaxed upward stance and perceiving a virtual visual environment (VVE), we recorded postural reactions to isolated visual and vestibular stimulations or their combinations. Lateral displacements of the visualized virtual scene were used as visual stimuli. The vestibular apparatus was stimulated by application of near-threshold galvanic current pulses to the proc. mastoidei of the temporal bones. Isolated VVE shifts evoked mild, nonetheless clear, body tilts readily distinguished in separate trials; at the same time, postural effects of isolated vestibular stimulation could be detected only after averaging of several trials synchronized with respect to the beginning of stimulation. Under conditions of simultaneous combined presentation of visual and vestibular stimuli, the direction of the resulting postural responses always corresponded to the direction of responses induced by VVE shifts. The contribution of an afferent volley from the vestibular organ depended on the coincidence/mismatch of the direction of motor response evoked by such a volley with the direction of response to visual stimulation. When both types of stimulations evoked unidirectional body tilts, postural responses were facilitated, and the resulting effect was greater than that of simple summation of the reactions to isolated actions of the above stimuli. In the case where isolated galvanic stimulation evoked a response opposite with respect to that induced by visual stimulation, the combined action of these stimuli of different modalities evoked postural responses identical in their magnitude, direction, and shape to those evoked by isolated visual stimulation. The above findings allow us to conclude that the effects of visual afferent input on the vertical posture under conditions of our experiments clearly dominate. In general, these results confirm the statement that neuronal structures involved in integrative processing of different afferent volleys preferably select certain type of afferentation carrying more significant or more detailed information on displacements (including oscillations) of the body in space.     

On the ability of neurons in the barn owl's inferior colliculus to sense brief appearances of interaural time difference

Summary This paper investigates the ability of neurons in the barn owl's (Tyto alba) inferior colliculus to sense brief appearances of interaural time difference (ITD), the main cue for azimuthal sound localization in this species. In the experiments, ITD-tuning was measured during presentation of a mask-probe-mask sequence. The probe consisted of a noise having a constant ITD, while the mask consisted of binaurally uncorrelated noise. Collicular neurons discriminated between the probe and masking noise by showing rapid changes from untuned to tuned and back to untuned responses.The curve describing the relation between probe duration and the degree of ITD-tuning resembled a leaky-integration process with a time constant of about 2 ms. Many neurons were ITD-tuned when probe duration was below 1 ms. These extremely short effective probe durations are interpreted as evidence for neuronal convergence within the pathway computing ITD. The minimal probe duration necessary for ITD-tuning was independent of the bandwidth of the neurons' frequency tuning and also of the best frequency of a neuron. Many narrowly tuned neurons having different best frequencies converge to form a broad-band neuron. To yield the short effective probe durations the convergence must occur in strong temporal synchronism.Abbreviations ICc central nucleus of the inferior colliculus; - ICx external nucleus of the inferior colliculus; - ITD interaural time difference - LP Likelihood parameter     

Fractal rotation isolates mechanisms for form-dependent motion in human vision

Here, we describe a motion stimulus in which the quality of rotation is fractal. This makes its motion unavailable to the translation-based motion analysis known to underlie much of our motion perception. In contrast, normal rotation can be extracted through the aggregation of the outputs of translational mechanisms. Neural adaptation of these translation-based motion mechanisms is thought to drive the motion after-effect, a phenomenon in which prolonged viewing of motion in one direction leads to a percept of motion in the opposite direction. We measured the motion after-effects induced in static and moving stimuli by fractal rotation. The after-effects found were an order of magnitude smaller than those elicited by normal rotation. Our findings suggest that the analysis of fractal rotation involves different neural processes than those for standard translational motion. Given that the percept of motion elicited by fractal rotation is a clear example of motion derived from form analysis, we propose that the extraction of fractal rotation may reflect the operation of a general mechanism for inferring motion from changes in form.     

Fooling the Eyes: The Influence of a Sound-Induced Visual Motion Illusion on Eye Movements

The question of whether perceptual illusions influence eye movements is critical for the long-standing debate regarding the separation between action and perception. To test the role of auditory context on a visual illusion and on eye movements, we took advantage of the fact that the presence of an auditory cue can successfully modulate illusory motion perception of an otherwise static flickering object (sound-induced visual motion effect). We found that illusory motion perception modulated by an auditory context consistently affected saccadic eye movements. Specifically, the landing positions of saccades performed towards flickering static bars in the periphery were biased in the direction of illusory motion. Moreover, the magnitude of this bias was strongly correlated with the effect size of the perceptual illusion. These results show that both an audio-visual and a purely visual illusion can significantly affect visuo-motor behavior. Our findings are consistent with arguments for a tight link between perception and action in localization tasks.     

A mismatch negativity elicited with stationary and moving auditory images of different azimuth positions

Characteristics of mismatch negativity elicited by dichotic stimulation were examined using deviant stimuli simulating movement of fused auditory images towards the standard stimuli or in the reverse direction. The effect of stationary deviants localized at 90 degrees in respect to standards was also measured. The standard stimuli were localized near either of ears or along the head midline. The spatial locations were produced by introducing interaural time differences into the click trains. All deviant stimuli evoked the mismatch negativity. The deviants moving from standards seem to evoke the lowest mismatch negativity with the longest latency at all azimuthal locations of standard stimuli. Besides, the deviant shift from standards proved to be the only direction at which the characteristics of mismatch negativity depended upon the standard's azimuth. It is seems that the discrimination of interaural time delay is essentially dependent on the pattern of interaural delay changes at the moment when the deviant occurs.