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Direction specific error patterns during continuous tracking of the subjective visual vertical
Abstract
The aim of this study was to characterize the error pattern of continuously tracking the perceived earth-vertical during roll rotations from upright to right or left ear-down and from right or left ear-down to upright. We compared the tracking responses of two paradigms, which either continuously activated the otoliths organs alone (constant velocity tilt) or both the otolith organs and the semicircular canals (constant acceleration tilt). The tracking responses of the subjective visual vertical showed characteristic differences depending on starting position and tilt direction relative to gravity. The error patterns in the constant-velocity and constant-acceleration tilt paradigm were reversed. Estimations during tracking, when otolith information was continuously changing, were more precise compared to estimations following fast tilts to fixed roll tilt positions. We conclude that the central processing underlying these perceptual tracking responses requires, besides the otolith input, information from the vertical semicircular canals.
... Our staircase procedure has a clear advantage when compared to a continuous-tracking method. The latter was used by Keusch et al. (2004), who asked subjects to continuously align a luminous line with the direction of gravity while they were being rotated. With this approach, measurements at different tilt angles are clearly not independent and the time needed for the adjustment may affect the time course of the response. ...
... Others have tested verticality perception during earth-horizontal and earth-vertical yaw rotation (Pavlou et al., 2003) or at intermediate tilt angles Wood et al., 2007). Keusch et al. (2004) undertook a dynamic roll-tilt study in a limited tilt range using constant-velocity and constant-acceleration rotation and reported that error patterns depend on the rotation profile. All these studies have suggested that signals from the semicircular canals are an important factor in verticality perception. ...
... From the perspective of the model, the fact that an onset effect showed up in both the dynamic SVV and SBT data may indicate that it is already present in signalĝ, but its origin remains unclear. One could speculate that it was caused by activation of the vertical semicircular canals (Jaggi- Keusch et al., 2004;Pavlou et al., 2003) or that a computational delay, which is not in the model, is involved (see Discussion, section "Disambiguation process"). ...
This thesis describes the results of a research project that focused on how visual and vestibular signals are used by the human brain to maintain spatial orientation and visual stability. Given the limitations of the vestibular sensors in terms of bandwidth and precision, outlined in chapter 1, achieving this is far from trivial. Existing spatial orientation models have specified in some detail how the brain could cope with these imperfections when it comes to reconstructing three crucial variables: angular rotation of the body in space, body-tilt with respect to gravity and linear translation of the body. Our objective was to collect extensive quantitative data sets in various static and dynamic conditions, for comparison with the model predictions. In chapters two and three we quantified the selfmotion and verticality percept of human subjects that were rotated in yaw about an off-vertical axis (OVAR). The perceptual data were compared with two spatial orientation models: the frequency segregation hypothesis and the canal-otolith interaction model. In the fourth chapter, we tested whether an extended version of the canal-otolith interaction model could account for the verticality percept during three cycles of constant velocity rotation. In the final chapter, we investigated how the presence of a tilted visual frame influences the verticality percept of roll-tilted human observers and compared the results with two subjective visual vertical models.
... Reconstructing the orientation of a visual contour in terrestrial coordinates requires information about line orientation on the retina and about body tilt. According to the literature, bodytilt information may involve various sources such as the otoliths (Mittelstaedt, 1983), the semicircular canals (Pavlou et al., 2003;Keusch et al., 2004) and the somatosensory system (Bronstein et al., 1996;Anastasopoulos and Bronstein, 1999). A peripheral explanation of the A-E transition, in the sense that this phenomenon reflects a tilt-related discontinuity in the properties of primary sensory afferents, seems unlikely. ...
... Udo de Haes and Schöne (1970) attributed this finding to an aftereffect of the semicircular canals. Although there is indeed indirect evidence for a role of the canals in the subjective visual vertical Keusch et al., 2004;Pavlou et al., 2003), a problem with the Udo de Haes and Schöne (1970) hypothesis has always been that it cannot easily explain why the hysteresis is restricted to large tilt angles. Our analysis suggests a different origin for the hysteresis which also explains why this phenomenon occurs only at large tilts. ...
... Classical visual orientation studies, testing the sense of verticality under static tilt conditions, have strongly emphasized the role of the otoliths (Mittelstaedt, 1983). Other studies, using rapid tilt paradigms, found canal-related effects, but still considered the otoliths as the main source of information Keusch et al., 2004;Udo de Haes and Schöne, 1970). Also a recent study by Klier et al. (2005), which compared saccadic updating after upright and supine roll tilts involving vigorous canal stimulation, concluded that the contribution from graviceptive signals is critical. ...
This thesis describes the results of a research project to investigate vestibular aspects of visual updating in roll-tilted subjects. The focus of the first part is on errors in verticality perception of tilted subjects. Although tilted subjects accurately known how much they are tilted and also know the line orientation relative to their body, they are not able to estimate the line orientation relative to gravity. An important model that tries to explain this relies solely on otolith signals, but other studies suggests that canal signals play a role. Our results confirm that the canals do not play a role at tilt up to about 135 degrees. However, at large tilts a sudden transition to errors of opposite sign occurs. After the transition, we find canal effects and also a strong correlation between verticality perception and body-tilt perception. Our study is the first to thoroughly quantify and discuss these phenomena. The second part of this thesis focuses on another question: how are signals of the otoliths and semicircular canals combined to update the internal representation of visual space? We tested visual stability during dynamic head rotations at different frequencies, in conditions with and without otolith cues. Our results show that subjects severely underestimate head rotation. An illusory translation percept is present at higher frequencies. The results shows that the canal contribution to visual orientation perception has high-pass characteristics. The otolith contribution is low-pass and relatively small. Current models cannot explain these findings. We suggest that the brain forms two estimates of head tilt, one based on otolith signals and one based on canal signals, and that the final estimate is a weighted sum of these two. The violations of visual position constancy are compatible with leaky integration of an internal estimate of head acceleration.
... Classical visual orientation studies, testing the sense of verticality under static tilt conditions, have strongly emphasized the role of the otoliths (Mittelstaedt 1983). Other studies, using rapid tilt paradigms, found canal-related effects, but still considered the otoliths as the main source of information (Jaggi-Schwarz et al. 2003;Keusch et al. 2004;Udo de Haes and Schöne 1970). Also a recent study by Klier et al. (2005), which compared saccadic updating after upright and supine roll tilts involving vigorous canal stimulation, concluded that the contribution from graviceptive signals is critical. ...
... We are thus left with the third possibility: to use both gravity cues and rotational cues in parallel, whenever the occasion arises. That rotational cues can influence visual space perception in the upright condition has been suggested before (Jaggi-Schwarz and Hess 2003;Jaggi-Schwarz et al. 2003;Keusch et al. 2004;Udo de Haes and Schöne 1970). Furthermore, it is known that optic-flow stimulation with a rotating random-dot pattern about the line of sight has a clear effect on the visual subjective vertical (Dichgans et al. 1972;Held et al. 1975;Mittelstaedt 1995). ...
... Studies of the subjective visual vertical under static conditions have suggested a dominant otolith contribution (Kaptein and Van Gisbergen 2004;Mittelstaedt 1983). Other studies, using dynamic conditions (Jaggi-Schwarz and Hess 2003;Jaggi-Schwarz et al. 2003;Keusch et al. 2004;Udo de Haes and Schöne 1970), did find canal-related effects, but these were considered relatively small compared with the otolith contribution, or were seen as a sign of canal-otolith interaction. Unfortunately, since such experiments cannot be carried out in supine, canal and otolith contributions could not easily be distinguished. ...
Using vestibular sensors to maintain visual stability during changes in head tilt, crucial when panoramic cues are not available, presents a computational challenge. Reliance on the otoliths requires a neural strategy for resolving their tilt/translation ambiguity, such as canal-otolith interaction or frequency segregation. The canal signal is subject to bandwidth limitations. In this study, we assessed the relative contribution of canal and otolith signals and investigated how they might be processed and combined. The experimental approach was to explore conditions with and without otolith contributions in a frequency range with various degrees of canal activation. We tested the perceptual stability of visual line orientation in six human subjects during passive sinusoidal roll tilt in the dark at frequencies from 0.05 to 0.4 Hz (30 degrees peak to peak). Because subjects were constantly monitoring spatial motion of a visual line in the frontal plane, the paradigm required moment-to-moment updating for ongoing ego motion. Their task was to judge the total spatial sway of the line when it rotated sinusoidally at various amplitudes. From the responses we determined how the line had to be rotated to be perceived as stable in space. Tests were taken both with (subject upright) and without (subject supine) gravity cues. Analysis of these data showed that the compensation for body rotation in the computation of line orientation in space, although always incomplete, depended on vestibular rotation frequency and on the availability of gravity cues. In the supine condition, the compensation for ego motion showed a steep increase with frequency, compatible with an integrated canal signal. The improvement of performance in the upright condition, afforded by graviceptive cues from the otoliths, showed low-pass characteristics. Simulations showed that a linear combination of an integrated canal signal and a gravity-based signal can account for these results.
... Reconstructing the orientation of a visual contour in terrestrial coordinates requires information about line orientation on the retina and about body tilt. According to the literature, body-tilt information may involve various sources such as the otoliths (Mittelstaedt 1983), the semicircular canals (Keusch et al. 2004; Pavlou et al. 2003) and the somatosensory system (Anastasopoulos and Bronstein 1999; Bronstein et al. 1996). A peripheral explanation of the A-E transition, in the sense that this phenomenon reflects a tilt-related discontinuity in the properties of primary sensory afferents, seems unlikely. ...
... Udo de Haes and Schöne (1970) attributed this finding to an aftereffect of the semicircular canals. Although there is indeed indirect evidence for a role of the canals in the subjective visual vertical ( Keusch et al. 2004; Pavlou et al. 2003), a problem with the Udo de Haes and Schöne (1970) hypothesis has always been that it cannot easily explain why the hysteresis is restricted to large tilt angles. Our analysis suggests a different origin for the hysteresis which also explains why this phenomenon occurs only at large tilts. ...
A striking feature of visual verticality estimates in the dark is undercompensation for lateral body tilt. Earlier studies and models suggest that this so-called Aubert (A) effect increases gradually to around 130 degrees tilt and then decays smoothly on approaching the inverted position. By contrast, we recently found an abrupt transition toward errors of opposite sign (E effect) when body tilt exceeded 135 degrees . The present study was undertaken to clarify the nature of this transition. We tested the subjective visual vertical in stationary roll-tilted human subjects using various rotation paradigms and testing methods. Cluster analysis identified two clearly separate response modes (A or E effect), present in all conditions, which dominated in different but overlapping tilt ranges. Within the overlap zone, the subjective vertical appeared bistable on repeated testing with responses in both categories. The tilt range where bistability occurred depended on the direction of the preceding rotation (hysteresis). The overlap zone shifted to a smaller tilt angle when testing was preceded by a rotation through the inverted position, compared with short opposite rotations from upright. We discuss the possibility that the A-E transition reflects a reference shift from compensating line settings for the head deviation from upright to basing them on the tilt deviation of the feet from upright. In this scenario, both the A and the E effect reflect tilt undercompensation. To explain the hysteresis and the bistability, we propose that the transition is triggered when perceived body tilt, a signal with known noise and hysteresis properties, crosses a fixed threshold.
... Others have tested verticality perception during earth-horizontal (Mittelstaedt et al. 1989) and earthvertical yaw rotation (Pavlou et al. 2003) or at intermediate tilt angles (Vingerhoets et al. 2007;Wood et al. 2007). Keusch et al. (2004) undertook a dynamic roll-tilt study in which subjects were rotated from upright to just beyond horizontal and vice versa using constant velocity or constant acceleration and reported that error patterns depend on the rotation profile. ...
... From the perspective of the model, the fact that an onset effect showed up in both the dynamic SVV and SBT data may indicate that it is already present in signal ĝ, but its origin remains unclear. One could speculate that it was caused by activation of the vertical semicircular canals Keusch et al. 2004;Pavlou et al. 2003) or that a computational delay, which is not incorporated in the model, is involved (see DISCUSSION, Disambiguation process). ...
To assess the effects of degrading canal cues for dynamic spatial orientation in human observers, we tested how judgments about visual-line orientation in space (subjective visual vertical task, SVV) and estimates of instantaneous body tilt (subjective body-tilt task, SBT) develop in the course of three cycles of constant-velocity roll rotation. These abilities were tested across the entire tilt range in separate experiments. For comparison, we also obtained SVV data during static roll tilt. We found that as tilt increased, dynamic SVV responses became strongly biased toward the head pole of the body axis (A-effect), as if body tilt was underestimated. However, on entering the range of near-inverse tilts, SVV responses adopted a bimodal pattern, alternating between A-effects (biased toward head-pole) and E-effects (biased toward feet-pole). Apart from an onset effect, this tilt-dependent pattern of systematic SVV errors repeated itself in subsequent rotation cycles with little sign of worsening performance. Static SVV responses were qualitatively similar and consistent with previous reports but showed smaller A-effects. By contrast, dynamic SBT errors were small and unimodal, indicating that errors in visual-verticality estimates were not caused by errors in body-tilt estimation. We discuss these results in terms of predictions from a canal-otolith interaction model extended with a leaky integrator and an egocentric bias mechanism. We conclude that the egocentric-bias mechanism becomes more manifest during constant velocity roll-rotation and that perceptual errors due to incorrect disambiguation of the otolith signal are small despite the decay of canal signals.
... Our staircase procedure has a clear advantage when compared with a continuous-tracking method. The latter was used by Keusch et al. (2004), who asked subjects to continuously align a luminous line with the direction of gravity while they were being rotated. With this approach, measurements at different tilt angles are clearly not independent and the time needed for the adjustment may affect the time course of the response. ...
During prolonged rotation about a tilted yaw axis, often referred to as off-vertical axis rotation (OVAR), a percept of being translated along a conical path slowly emerges as the sense of rotation subsides. Recently, we found that these perceptual changes are consistent with a canal-otolith interaction model that attributes the illusory translation percept to improper interpretation of the ambiguous otolith signals. The model further predicts that the illusory translation percept must be accompanied by slowly worsening tilt underestimates. Here, we tested this prediction in six subjects by measuring the time course of the subjective visual vertical (SVV) during OVAR stimulation at three different tilt-rotation speed combinations, in complete darkness. Throughout the 2-min run, at each left-ear-down and right-ear-down position, the subject indicated whether a briefly flashed line deviated clockwise or counterclockwise from vertical to determine the SVV with an adaptive staircase procedure. Typically, SVV errors indicating tilt underestimation were already present at rotation onset and then increased exponentially to an asymptotic value, reached at about 60 s after rotation onset. The initial error in the SVV was highly correlated to the response error in a static tilt control experiment. The subsequent increase in error depended on both rotation speed and OVAR tilt angle, in a manner predicted by the canal-otolith interaction model. We conclude that verticality misjudgments during OVAR reflect a dynamic component linked to canal-otolith interaction, superimposed on a tilt-related component that is also expressed under stationary conditions.
The vestibular system provides information for spatial orientation. However, this information is ambiguous: because the otoliths sense the gravito-inertial force, they cannot distinguish gravitational and inertial components. As a consequence, prolonged linear acceleration of the head can be interpreted as tilt, referred to as the somatogravic effect. Previous modeling work suggests that the brain disambiguates the otolith signal according to the rules of Bayesian inference, combining noisy canal cues with the a priori assumption that prolonged linear accelerations are unlikely. Within this modeling framework the noise of the vestibular signals affects the dynamic characteristics of the tilt percept during linear whole-body motion. To test this prediction, we devised a novel paradigm to psychometrically characterize the dynamic visual vertical - as a proxy for the tilt percept - during passive sinusoidal linear motion along the inter-aural axis (0.33Hz motion frequency, 1.75m/s2 peak acceleration, 80cm displacement). While subjects (n=10) kept fixation on a central body-fixed light, a line was briefly flashed (5ms) at different phases of the motion, the orientation of which had to be judged relative to gravity. Consistent with the model's prediction, subjects showed a phase-dependent modulation of the dynamic visual vertical, with a subject-specific phase-shift with respect to the imposed acceleration signal. The magnitude of this modulation was smaller than predicted, suggesting a contribution of non-vestibular signals to the dynamic visual vertical. Despite their dampening effect, our findings may point to a link between the noise components in the vestibular system and the characteristics of dynamic visual vertical.
The purpose of this doctoral dissertation is twofold: (1) to contribute to a better comprehension of the processes implied in the egocentric perception of a visual object in gravitational earth space, and (2) to study the role of the egocentric reference in the visual
perception of the direction of gravity. Data from a first set of experiments showed that only roll body tilts induced errors in the visual localization and orientation of body midline. However, the deviation was in the direction opposite to body tilt for the localization task suggesting the implication of the vestibulo-ocular reflex, whereas the deviation was in the direction of body tilt for of the orientation task suggesting the implication of the tactile somaesthetic. The second set of experiments suggested that, when the head and trunk were dissociated, the cephalic segment play an important role in the egocentric perception of the orientation of the trunk by exerting an attraction in its direction in situation of sensory discordance (vibration of neck muscles and microgravity). However, these deviations seemed independent of the efficiency of cervical information. A last experiment revealed that the deviation in the perception of the orientation of the egocentric axis in the direction of the body tilt could contribute to the Aubert effect. The perception of Z-axis would have consequences not only on the perception of egocentric space but also on the judgement of the gravitational vertical. These results give to subjective body midline a heuristic value in the space orientation.
[Purpose] To investigate whether postures of the head and trunk in the frontal plane affect the subjective visual vertical (SVV). [Subjects] Nineteen healthy adults were enrolled. [Methods] We measured SVV under five sitting conditions: upright, inclining the head, inclining the trunk, inclining the trunk with the head upright, inclining both the head and trunk. Subjects were instructed to stop a moving line on a PC monitor when they thought that the line was vertical. The values of SVV, and the differences in degree between the true vertical and subjective vertical, were compared among the five conditions. [Results] The absolute values of SVV in the upright and inclining the trunk with the head upright conditions were significantly smaller than those in the three other conditions. The values of SVV in the inclining the trunk condition was significantly smaller than those in the inclining the head or in inclining the head and trunk conditions. [Conclusions] The effects of posture on SVV measurement must be considered.
Neuronal connections and pathways underlying sacculocollic reflexes were studied by intracellular recordings from neck extensor and flexor motoneurons in decerebrate cat. Bipolar electrodes were placed within the left saccular nerve, whereas other branches of the vestibular nerve were removed in the inner ear. To prevent spread of stimulus current to other branches of the vestibular nerve, the saccular nerve and the electrodes were covered with warm semisolid paraffin-Vaseline mixture. Saccular nerve stimulation evoked disynaptic (1.8-3.0 ms) excitatory postsynaptic potentials (EPSPs) in ipsilateral neck extensor motoneurons and di- or trisynaptic (1.8-4.0 ms) EPSPs in contralateral neck extensor motoneurons, and di- and trisynaptic (1.7-3.6 ms) inhibitory postsynaptic potentials (IPSPs) in ipsilateral neck flexor motoneurons and trisynaptic (2.7-4.0 ms) IPSPs in contralateral neck flexor motoneurons. Ipsilateral inputs were about twice as strong as contralateral ones to both extensor and flexor motoneurons. To determine the pathways mediating this connectivity, the lateral part of the spinal cord containing the ipsilateral lateral vestibulospinal tract (i-LVST) or the central part of the spinal cord containing the medial vestibulospinal tracts (MVSTs) and possibly reticulospinal fibers (RSTs) were transected at the caudal end of the C1 segment. Subsequent renewed intracellular recordings following sacculus nerve stimulation indicated that the pathway from the saccular nerve to the ipsilateral neck extensor motoneurons projects though the i-LVST, whereas the pathways to the contralateral neck extensors and to the bilateral neck flexor motoneurons descend in the MVSTs/RSTs. Our data show that sacculo-neck reflex connections display a qualitatively bilaterally symmetrical innervation pattern with excitatory connections to both neck extensor motoneuron pools, and inhibitory connections to both neck flexor motoneuron pools. This bilateral organization contrasts with the unilateral innervation scheme of the utriculus system. These results suggest a different symmetry plane along which sacculus postural reflexes are organized, thus supplementing the reference planes of the utriculus system and allowing the gravistatic system to represent all three translational spatial degrees of freedom. We furthermore suggest that the sacculocollic reflex plays an important role in maintaining the relative position of the head and the body against the vertical linear acceleration of gravity.
Previous testing of the ability to set a luminous line to the direction of gravity in passively-tilted subjects, in darkness, has revealed a remarkable pattern of systematic errors at tilts beyond 60 degrees, as if body tilt is undercompensated or underestimated (Aubert or A-effect). We investigated whether these consistent deviations from orientation constancy can be avoided during active body tilt, where more potential cues about body tilt (e.g. proprioception and efference copy) are available. The effects of active body tilt on the subjective vertical and on the perception of self tilt were studied in six subjects. After adopting a laterally-tilted posture, while standing in a dark room, they indicated the subjective vertical by adjusting a visual line and gave their verbal estimate of head orientation, expressed on a clock scale. Head roll tilts covered the range from -150 degrees to +150 degrees. The subjective vertical results showed no sign of improvement. Actively-tilted subjects still exhibited the same pattern of systematic errors that characterised their performance during passive tilt. Random errors in this task showed a steep monotonic increase with tilt angle, as in earlier passive tilt experiments. By contrast, verbal head-tilt estimates in the active experiments showed a clear improvement and were now almost devoid of systematic errors, but the noise level remained high. Various models are discussed in an attempt to clarify how these task-related differences and the selective improvement of the self-tilt estimates in the active experiments may have come about.
It has been proposed that a vestibular reflex originating in the otolith organs and other body graviceptors modulates sympathetic activity during changes in posture with regard to gravity. To test this hypothesis, we selectively stimulated otolith and body graviceptors sinusoidally along different head axes in the coronal plane with off-vertical axis rotation (OVAR) and recorded sympathetic efferent activity in the peroneal nerve (muscle sympathetic nerve activity, MSNA), blood pressure, heart rate, and respiratory rate. All parameters were entrained during OVAR at the frequency of rotation, with MSNA increasing in nose-up positions during forward linear acceleration and decreasing when nose-down. MSNA was correlated closely with blood pressure when subjects were within +/-90 degrees of nose-down positions with a delay of 1.4 s, the normal latency of baroreflex-driven changes in MSNA. Thus, in the nose-down position, MSNA was probably driven by baroreflex afferents. In contrast, when subjects were within +/-45 degrees of the nose-up position, i.e., when positive linear acceleration was maximal along the naso-ocipital axis, MSNA was closely related to gravitational acceleration at a latency of 0.4 s. This delay is too short for MSNA changes to be mediated by the baroreflex, but it is compatible with the delay of a response originating in the vestibular system. We postulate that a vestibulosympathetic reflex, probably originating mainly in the otolith organs, contributes to blood pressure maintenance during forward linear acceleration. Because of its short latency, this reflex may be one of the earliest mechanisms to sustain blood pressure upon standing.
The aim of this study was to test the hypothesis that optimal activation of both the semicircular canals and the otoliths provides reliable vestibular cues about self-orientation in space. For this, we measured the ability of subjects to estimate the subjective vertical immediately, 20 s and 90 s after a rapid tilt (180 degrees /s(2)) from upright into different roll positions between 90 degrees left and right side down. Subjects had to estimate the earth-vertical and earth-horizontal direction in the dark by (a) setting a luminous line, (b) performing saccades, and (c) verbally declaring body position relative to gravity. The mean error curves from the three paradigms showed consistent E (Müller)- and A (Aubert)-effects, which did not significantly change over time. Horizontal and vertical saccade tasks exhibited different response characteristics, as previously reported by others, which likely reflect different computation mechanisms. The verbal estimation paradigm yielded complementary results to those of the luminous line paradigm and vertical saccade task. The E-effect of the luminous line and the vertical saccade paradigm might be explained by a bias towards earth-vertical due to interactions of vestibular and neck afferent signals. The invariably small A-effect of the luminous line and the vertical saccade paradigm probably reflects somatosensory signals that had relatively weak influence in our experiments. We conclude that phasic activation of the vestibular system reduces the influence of non-vestibular cues observed in low tilt velocity or static experiments. Although this activation generates an E-effect, the total error in the range of +/-90 degrees is reduced.
Unlabelled:
The subjective visual vertical (SVV) is usually considered a measure of otolith function. Herewith we investigate the influence of semicircular canal (SCC) stimulation on the SVV by rotating normal subjects in yaw about an earth-vertical axis, with velocity steps of +/- 90 degrees /s, for 60 s. SVV was assessed by setting an illuminated line to perceived earth vertical in darkness, during a per- and postrotary period. Four head positions were tested: upright, 30 degrees backward (chin up) or forward, and approximately 40 degrees forward from upright. During head upright/backward conditions, a significant SVV tilt (P < 0.01) in the direction opposite to rotation was found that reversed during postrotary responses. The rotationally induced SVV tilt had a time constant of decay of approximately 30 s. Rotation with the head 30 degrees forward did not affect SVV, whereas the 40 degrees forward tilt caused a direction reversal of SVV responses compared with head upright/backward. Spearman correlation values (Rho) between individual SCC efficiencies in different head positions and mean SVV tilts were 0.79 for posterior, 0.34 for anterior, and - 0.80 for horizontal SCCs. Three-dimensional video-oculography showed that SVV and torsional eye position measurements were highly correlated (0.83) and in the direction opposite to the slow phase torsional vestibuloocular reflex.
In conclusion:
1) during yaw axis rotation without reorientation of the head with respect to gravity, the SVV is influenced by SCC stimulation; 2) this effect is mediated by the vertical SCCs, particularly the posterior SCCs; 3) rotationally induced SVV changes are due to torsional ocular tilt; 4) SVV and ocular tilts occur in the "anticompensatory," fast phase direction of the torsional nystagmus; and 5) clinically, abnormal SVV tilts cannot be considered a specific indication of otolith system dysfunction.
This study investigated the reciprocal relation between estimation of body tilt and visual vertical by using self-controlled passive body tilts at constant velocity (slow tilts with no semicircular canal activation) or constant acceleration (rapid tilts with canal activation). In both conditions, the visual vertical was overestimated in the luminous line setting paradigm, whereas body tilt was underestimated in the position estimation paradigm. These errors were larger after slow than rapid tilts. During slow tilts, the range of actually reached positions was on average underestimated by about 25% with respect to the desired positions. Interestingly, there were no significant differences in the estimated positions for tilts in the roll and pitch plane. Most remarkably, in the range of +/-45 degrees the resulting means of position and luminous line setting errors of the velocity and acceleration paradigms as a function of the desired roll positions were close to zero. Furthermore, the resulting means of the two paradigms showed a high correlation in the tested range of +/-90 degrees. We conclude that: (a). the otoliths provide the main information for the spatial reference for both the estimation of body positions and the luminous line settings, at least in the range of about +/-45 degrees where the resulting mean errors between the two paradigms are close to zero, and (b). coactivation of semicircular canals improves the estimations.
1 Introduction.- 2 Peripheral Morphology.- 3 Biophysics of the Peripheral End Organs.- 4 Mechanoneural Transduction and the Primary Afferent Response.- 5 Labyrinthine Input to the Vestibular Nuclei and Reticular Formation.- 6 The Vestibular System and the Cerebellum.- 7 The Vestibulospinal System.- 8 The Vestibuloocular System.- References.
The subjective vertical (SV) was measured at various positions of roll-tilt (R). Positions R90-right, R 45-right, R0, R45-left, R90-left were reached either in clockwise sequence (i.e. starting with R 90-left) or in counterclockwise sequence (starting with R90-right); position R135-right was attained from R 110-right or R 160-right. The SV was affected by the preceding tilt (hysteresis). Clockwise position sequence produced, for example, a counterclockwise SV deviation (from the medium value at the obtained position) as though indicating a more advanced tilt position (Fig. 5). It is concluded that the aftereffects and hysteresis differences in perception of position and of SV depend on adaptational processes in the somatoreception system which interacts with the labyrinth posture-receptors.
A short review is presented of recent work on neural circuits responsible for the labyrinth's control of head movement.
Results of the five experiments are consistent with the following generalizations. Canal-mediated turn perception (pitch, roll, or yaw) in earth-horizontal or earth-vertical plane, is suppressed in direct relationship to the magnitude of a linear acceleration vector lying in the plane of a responding canal when the magnitude of the linear vector is constant or increasing and when its direction is either fixed or rotating in the same direction as the concomitant canal signal. Canal-mediated turn perception (pitch, roll, or yaw) is not suppressed by a coplanar linear vector that is counterrotating relative to the canal signal. Change in perceived attitude (pitch, roll, or yaw) is very sluggish in the absence of concordant canal information; attitude change may not be an immediate otolith-mediated perceptual event but a slowly developing perception dependent upon cognitive appreciation of an immediate otolith angular position signal. Otolith phasic neural units, unreinforced by appropriate canal signals, may contribute more to a brief linear velocity component in perception than to rate of attitude change. Otolith-mediated attitude perception within a given earth-vertical plane can be distorted by strong coplanar angular velocity canal information. Once distorted, return to veridical attitude perception can be gradual because, in the absence of complimentary canal or visual information, recovery is dependent upon relatively slow cognitive appreciation of a prevailing otolith position signal. Several attractive hypotheses relating to the dynamics of attitude perception can only be tested by substantially more data on the dynamics of spatial orientation perception. Most of our objectives cannot be achieved without models that yield valid prediction of the dynamics of spatial orientation perception. All of the observations in these experiments were carried out in darkness, or, in the simulated catapult experiment, without external visual reference. Various forms of visual information will change the dynamics of spatial orientation perception. My discussion has been limited to consideration of the vestibular system, as though the canal and otolith systems completely controlled the dynamics of spatial orientation perceptions. Obviously other partners in the dynamics of postural control, including vision, proprioception, and expectation, must be included in this challenging field of research. Dedication to stereotyped ideas about objectivity in the 20th century has hindered advancement of knowledge on the dynamics of spatial orientation perception relative to rate of progress achieved by several scientists of the 18th and 19th centuries, who provided word pictures of perceived motions and tilts along with descriptions of the motions that engendered the pictures.(ABSTRACT TRUNCATED AT 400 WORDS)
Voluntary gaze control obeys the law of Listing. This law specifies the torsion of the eye in every direction of gaze, when the so-called "primary position" of the eye is known. In the present article, some interesting relations between Listing's Law and the primary position on the one hand, and eye muscle innervation on the other hand are derived. A new vectorial description of eye position is introduced which permits to represent Listing's Law by a very simple equation. It also allows to approximate the transformation between eye muscle innervation and eye position by a 3 x 3-matrix in a large field of gaze and with quantities of innervation which are directly related to motoneuron firing rates. It is shown that these innervation quantities must be linearly coupled to yield Listing's Law and that the parameters of this coupling determine the primary position. Finally, relations between innervations and eye muscle forces are considered, and a hypothesis concerning the cooperation of voluntary gaze control and otolith or vergence inputs is presented.
Eight men completed an experiment in which they were rotated about an Earth-horizontal axis at velocities of 10 and 30 rpm. Both nystagmus and subjective estimates of body position in space were modified by the higher rate of rotation. Subjects who gave essentially veridical estimates of body position at 10 rpm became disoriented at 30 rpm and gave responses closely resembling those of subjects with labyrinthine dysfunction. Subjects who produced sustained unidirectional horizontal nystagmus during constant velocity rotation at 10 rpm produced a reversing horizontal nystagmus during comparable intervals of rotation at 30 rpm. Nystagmus slow phase velocity for both 10 and 30 rpm exhibited a cyclic modulation which was related to orientation relative to gravity. As in previous studies, sickness was produced by rotation about a horizontal axis, and a relationship between mental task and incidence of sickness was again noted.
The effect of postrotatory vertical canal stimulation on nystagmus and apparent vertical was investigated as a function of the tilt position at stop in a vertical roll-plane. Nystagmus duration and number of beats as well as the effect on the apparent vertical increased with change of stop position from head-up to head-down. The results are interpreted in terms of a hypothesis which proposes a decline of effectiveness of the statolith organs with increasing degree of tilt. This is discussed with respect to related findings.
When a man is accelerated on a centrifuge, the direction of gravitoinertial vertical changes relative to his body. However, a lag occurs in his perception of this change. The hypothesis has been advanced that the perceptual lag in this situation is partly the result of a conflict between signals arising from the semicircular canals and from the otolith organs. To test this hypothesis, subjects were tilted in such a way that they received consistent semicircular canal and otolith signals. This was accomplished simply by tilting them 30 deg from upright in their frontal plane. Immediately after being tilted, these subjects made estimates of the vertical which were approximately accurate, and they continued to make accurate estimates throughout a 140 sec judgment period. The absence of a perceptual lag under these circumstances supports the hypothesis.
Based on new evidence and the extensive literature, this report develops an outline of a comprehensive theory of the subjective vertical (SV) in humans. Traditionally the large deviations of the SV from veridicality are attributed to a failure on the part of the gravity systems to correctly perform the necessary coordinate transformation on the visual system. It is experimentally demonstrated, however, that in the control of posture the gravity systems do in fact work close to perfection in positions where the deviations of the SV from the physical vertical are almost largest. Since also the visual system is known to process angular information veridically in the respective range, the intervention of a third agent is suggested, namely a tendency to shift the SV towards the person's own longitudinal axis (idiotropic vector). The predictions of the theory are confirmed experimentally, proving that not only the visual but also the haptic zenith is shifted towards the long axis by strongly correlated amounts, when the head is pitched backwards. The theory is also shown to be compatible with, or amenable to typical properties of the SV response characteristic [1], quantitative neurological data on primate gravity receptors [2], a theory of postural control worked out earlier [3], and a particular type of non-linear interaction also found in other orientation systems [4].
1. Intracellular recordings of synaptic potentials in extraocular motoneurons were studied to determine the connectivities between the utricular nerve and the extraocular motoneurons in cats. 2. Stimulating electrodes were placed within the left utricular nerve, while other branches of the vestibular nerve were removed. Subsequently, the N1 field potentials evoked by utricular nerve stimulation were recorded in the vestibular nuclei. The potential typically grew until reaching a plateau (submaximal stimulation). Stimulus spread to the other nerve branches appeared as an additional increase in N1 amplitude after the plateau discontinued (supramaximal stimulation). 3. Intracellular recordings were made from 200 identified motoneurons in the bilateral III, IV, and VI cranial nuclei. 4. Stimulation of the utricular nerve at submaximal intensity evoked a longer latency depolarizing and hyperpolarizing potentials in contra- and ipsilateral medial rectus motoneurons, respectively. Complex potentials with longer latencies also were recorded in ipsilateral inferior oblique and contralateral trochlear motoneurons after stimulation of the utricular nerve at a submaximal intensity. Monosynaptic and disynaptic connections between the utricular nerve and ipsilateral abducens motoneurons and interneurons were recorded as described previously. 5. The results of the present study confirm our initial findings that a disynaptic pathway from the utricular nerve to contralateral trochlear motoneurons is absent or very poorly developed, whereas polysynaptic circuits from the utricular nerve to inferior oblique and trochlear motoneurons may play a role in eye rotation during head tilt.
3 Medical Research Council Human Movement and Balance Unit, Section of Neuro-Otology, National Hospital for Neurology and Neurosurgery, Queen Square, London, WC1N 3BG, UK
The role of the otoliths in essential performances of human orientation is analyzed. The following interactions of the otoliths are considered:
1. The otoliths cooperate with graviceptors in the trunk in the perception of body posture. The truncal graviceptors turn out to yield on average 60% of the total gain.
2. The otoliths cooperate with proprioceptors in the head-to-trunk coordinate transformation. However, under static conditions, proprioceptors in the legs, although effective in the control of posture, neither affect the perception of posture nor of the visual vertical.
3. In contrast to the perception of posture, the perception of the visual vertical (SVV) receives the necessary gravity information exclusively from the otoliths. However, their output appears to be affected by a central nervous component that tends to rotate the SVV into the z-axis of head and trunk. A theory of vectorial summation of this component, the “idiotropic vector,” with the otolithic vector is able to explain the cause of the A- and E- effects, the increase of the variance of the SVV with the tilt angle, and the asymmetrical effect of rotatory visual flow.
4. Finally, it is shown that the otoliths, by the separation of the effects of tilt from those of translation, play an essential role in navigation by path integration.
The effects of peripheral vestibular diseases on the subjective visual vertical (SVV) are resumed and provide the basis for some insights into the otolith pathophysiology. With a normal range of 0 +/- 2 deg (when measured in an upright body position), the SVV was shifted by 11 +/- 6 deg toward the ipsilateral ear in 40 patients following an acute unilateral vestibular deafferentiation (UVD), but in the opposite direction in 9 of 52 patients after stapes surgery. These opposite effects suggest a push-pull mechanism of the pairs of otolith organs with respect to the SVV. The dissociation between the SVV and the perception of body position indicates influences by unconscious reflexive mechanisms such as ocular cyclotorsion on the SVV. In chronic UVD patients, lateral shifts of the subjects during constant angular velocity rotation into various eccentric positions (+/- 16 cm) revealed a shift of the "center of graviception" close to the remaining intact contralateral inner ear. To date, this seems to be the most consistent test for clinical identification of a chronic compensated unilateral loss of otolith function. The findings regarding asymmetries in otolithic sensitivity to medially and laterally directed roll-tilts remain controversial, probably mainly because of influences of extravestibular cues.
One of the key questions in spatial perception is whether the brain has a common representation of gravity that is generally accessible for various perceptual orientation tasks. To evaluate this idea, we compared the ability of six tilted subjects to indicate earth-centric directions in the dark with a visual and an oculomotor paradigm and to estimate their body tilt relative to gravity. Subjective earth-horizontal and -vertical data were collected, either by adjusting a visual line or by making saccades, at 37 roll-tilt angles across the entire range. These spatial perception responses and the associated body-tilt estimates were subjected to a principal-component analysis to describe their tilt dependence. This analysis allowed us to separate systematic and random errors in performance, to disentangle the effects of task (horizontal vs. vertical) and paradigm (visual vs. oculomotor) in the space-perception data, and to compare the veridicality of space perception and the sense of self-tilt. In all spatial-orientation tests, whether involving space-perception or body-tilt judgments, subjects made considerable systematic errors which mostly betrayed tilt underestimation [Aubert effect (A effect)] and peaked near 130 degrees tilt. However, the A effect was much smaller in body-tilt estimates than in spatial pointing, implying that the underlying signal processing must have been different. Pointing results obtained with the visual and the oculomotor paradigm were not identical either, but these differences, which were task-related (horizontal vs. vertical), were subtle in comparison. The tilt-dependent pattern of random errors (noisy scatter) was almost identical in visual and oculomotor pointing results, showing a steep monotonic increase with tilt angle, but was again clearly different in the body-tilt estimates. These findings are discussed in the context of a conceptual model in an attempt to explain how the different patterns of systematic and random errors in external-space and self-tilt perception may come about. The scheme proposes that basically similar computational mechanisms, working with different settings, may be responsible.
After an observer adapts to a moving stimulus, texture within a stationary stimulus is perceived to drift in the opposite direction-the traditional motion aftereffect (MAE). It has recently been shown that the perceived position of objects can be markedly influenced by motion adaptation. In the present study, we examine the selectivity of positional shifts resulting from motion adaptation to stimulus attributes such as velocity, relative contrast, and relative spatial frequency. In addition, we ask whether spatial position can be modified in the absence of perceived motion. Results show that when adapting and test stimuli have collinear carrier gratings, the global position of the object shows a substantial shift in the direction of the illusory motion. When the carrier gratings of the adapting and test stimuli are orthogonal (a configuration in which no MAE is experienced), a global positional shift of similar magnitude is found. The illusory positional shift was found to be immune to changes in spatial frequency and to contrast between adapting and test stimuli-manipulations that dramatically reduce the magnitude of the traditional MAE. The lack of sensitivity for stimulus characteristics other than direction of motion suggests that a specialized population of cortical neurones, which are insensitive to changes in a number of rudimentary visual attributes, may modulate positional representation in lower cortical areas.
Aim:
The vestibulosympathetic reflex refers to sympathetic nerve activation by the vestibular system. Animal studies indicate that the vestibular system assists in blood pressure regulation during orthostasis. Although human studies clearly demonstrate activation of muscle sympathetic nerve activity (MSNA) during engagement of the otolith organs, the role of the vestibulosympathetic reflex in maintaining blood pressure during orthostasis is not well-established. Examination of the vestibulosympathetic reflex with other cardiovascular reflexes indicates that it is a powerful and independent reflex. Ageing, which is associated with an increased risk for orthostatic hypotension, attenuates the vestibulosympathetic reflex. The attenuated reflex is associated with a reduction in arterial pressure.
Conclusion:
These findings suggest that the vestibulosympathetic reflex assists in blood pressure regulation in humans, but future studies examining this reflex in other orthostatically intolerant populations are necessary to address this hypothesis.
Recent studies aim to explain the duration and variability of behavioral reaction time in terms of neural processes. The time taken to make choices is occupied by at least two processes. Neurons in sensorimotor structures accumulate evidence that leads to alternative categorizations, while other neurons within these structures prepare and initiate overt responses. These distinct stages of stimulus encoding and response preparation support variable but flexible behavior.
How does conscious perception evolve following stimulus presentation? The idea that perception relies on discrete processing epochs has been often considered, but never widely accepted. The alternative, a continuous translation of the external world into explicit perception, although more intuitive and subjectively appealing, cannot satisfactorily account for a large body of psychophysical data. Cortical and thalamocortical oscillations in different frequency bands could provide a neuronal basis for such discrete processes, but are rarely analyzed in this context. This article reconciles the unduly abandoned topic of discrete perception with current views and advances in neuroscience.
Subjective phenomena and nystagmus were compared under two conditions of rotation, one in which the axis of rotation was vertical, i.e., aligned with gravity, and one in which the rotation-axis was horizontal. When the axis of rotation was horizontal, normal subjects exhibited nystagmus and sensations of rotation for periods of three minutes (and longer); deceleration produced very brief post-rotational reactions. L-D subjects, men presumed to be without vestibular function, did not exhibit nystagmus or report sensations similar to those of normal subjects for either the vertical or horizontal axis of rotation. Because prolonged nystagmus occurred almost exclusively in normal subjects when the rotation axis was horizontal, it is concluded that vestibular function is a necessary condition for this response and that it may be dependent upon the continuous reorientation of the otolith system relative to gravity. The results emphasize the importance of increasing our range of experimental observations to check the accuracy of theoretical predictions.
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