Low-frequency loud acoustic stimulation and goal-directed arm movements

Objective To analyse the effects of low-frequency loud acoustic stimulation on goal-directed movements involving the arm. Low-frequency sound stimulation impairs eye stability, evokes a subjective tilt of the visual surround in subjects presenting Tullio's phenomenon and induces, in normal subjects, short-latency evoked potentials in the neck and limb muscles.

Material and Methods Healthy subjects performed goal-directed movements in the horizontal plane with the right (dominant) arm to a fixed 3°-wide target positioned at an angle of 30°, with the instruction to perform fast and accurate movements to the target and to hold the final position. This fast-pointing task was performed in association with sound-induced vestibular–otolithic stimulation (110 dB SPL, 500 Hz) in the absence of visual guidance (i.e. pointing at a memorized target in the absence of target or pointer cues). Pointing errors were analysed by computing the constant errors made by the subjects (mean error). Pointing errors were also correlated with movement kinematics (movement duration, peak velocity, time to peak velocity) and with the reaction time of movement.

Results The low-frequency loud acoustic stimulation modified the final position of the arm-pointing task at the memorized target in the absence of vision.

Conclusion Goal-directed movements are achieved by means of sensory interactions between visual, somatosensory and vestibular information and the vestibular–otolithic signals contribute to the accuracy of voluntary arm movements.     

Coordination of a step with a reach

Although natural reaching behavior can easily include forward body movement, most laboratory studies of reaching have constrained the body to be stationary. Recently, however, it has been shown that normal subjects exhibit a different pattern of errors when attempting to pinpoint remembered target locations, depending on whether or not the reach includes a step. In the study of Flanders et al., these errors appeared to be due to the strategy of eye/head/hand coordination which normally comes into play when the body is moving toward the target. Since the spatial positioning of the head was found to partially explain the errors in hand placement, the present study examined the movements of patients with bilateral vestibular deficits in order to further analyze the whole-body coordination. Somewhat surprisingly, the patients exhibited the same pattern of head movement and the same errors in hand placement as did the control subjects. Nevertheless, the patients' movements clearly exhibited evidence for an abnormal decomposition of elbow extension and trunk rotation. Furthermore the patients' (spatial) hand paths were significantly more curved than those of control subjects and, only in the patients, paths to remembered targets were significantly more curved than paths to visible targets. Thus for movements to remembered targets, the patients tended to move the hand to the same incorrect spatial positions as control subjects but spatiotemporal aspects of the arm and body movement differed. The results are consistent with the idea that vestibular patients are overly dependent upon visual cues, and support the hypothesis that this stepping and reaching behavior is largely dependent upon a visual reference signal.     

选择注意与对侧声刺激对畸变产物耳声发射潜伏期的影响

目的 :观察选择注意和对侧声刺激对畸变产物耳声发射 (DPOAE)潜伏期的影响。方法 :对正常人15例 (30耳 ) ,进行视选择注意任务及对侧声刺激 ,以及两者同时出现时 DPOAE潜伏期测试。结果 :3种测试条件下 DPOAE潜伏期皆无变化。结论 :选择注意和对侧声刺激对 DPOAE潜伏期是否存在影响 ,尚需进一步研究。     

Dynamic visual acuity during linear acceleration along the inter-aural axis

We investigated visual-vestibular interactions during linear acceleration along the inter-aural axis. Eighteen healthy volunteers and two patients with central neurological diseases were subjected to transaural linear acceleration in the direction of gravity force (frequency: 0.5–1.5 Hz; amplitude: 5 cm). During linear acceleration, eye movements were recorded under three test conditions: eyes closed (EC), while staring at an imaginary target (IT) and during the testing of dynamic visual acuity (DVA). As parameters of evaluation we used the amplitude of horizontal eye movements, phase shift and the decrease of DVA threshold (DVAT). Under all test conditions, eye amplitude increased with rising stimulus frequency and exceeded, especially in the higher frequency range, a hypothetically calculated eye amplitude for smooth pursuit. The combination of a visual and vestibular input (DVA and IT) led to a better compensation (lower phase shift) than under vestibular stimulation alone (EC). Eye movements during low-frequency stimulation depended more on the visual system while responses in the higher frequency range were mainly triggered by the otolith organ. At 1.5 Hz the compensatory function of the visual-vestibular system was limited (rising phase shift) and DVAT decreased even in a significant number of healthy subjects. Patients with diseases of the central nervous system showed a higher phase shift and thus a stronger decrease of DVAT (two levels) already at a stimulus frequency of 1.25 Hz. Received: 29 May 1999 / Accepted: 2 September 1999     

Effects of increasing sound pressure level on lip and jaw movement parameters and consistency in young adults.

PURPOSE: Examination of movement parameters and consistency has been used to infer underlying neural control of movement. However, there has been no systematic investigation of whether the way individuals are asked (or cued) to increase loudness alters articulation. This study examined whether different cues to elicit louder speech induce different lip and jaw movement parameters or consistency. METHOD: Thirty healthy young adults produced two sentences (a) at comfortable loudness, (b) while targeting 10 dB SPL above comfortable loudness on a sound level meter, (c) at twice their perceived comfortable loudness, and (d) while multitalker noise was played in the background. Lip and jaw kinematics and acoustic measurements were taken. RESULTS: Each of the loud conditions resulted in a similar amount of SPL increase, about 10 dB. Speech rate was slower in the background noise condition. Changes to movement parameters and consistency (relative to comfortable) were different in the targeting condition as compared to the other loud conditions. CONCLUSIONS: The cues elicited different task demands, and therefore, different movement patterns were used by the speakers to achieve the target of increased loudness. Based on these results, cueing should be considered when eliciting increased vocal loudness in both clinical and research situations.     

Spatial navigation after surgical resection of an acoustic neuroma: pilot study

OBJECTIVE: To characterize navigation errors made by patients with the absence of vestibular function on one side owing to surgical resection of an acoustic neuroma. METHODS: Seventeen young (18-38 years) and 9 older healthy individuals (67-83 years), as well as 5 patients 2 to 20 months following surgery (37-61 years), were studied. They sidestepped laterally with eyes closed toward memorized targets located 1.25 m to their right or left. They stopped when they judged that they were in front of the target. The position of head and body markers was recorded in three dimensions with a six-camera Vicon 512 system (Oxford Metrics Ltd., Oxford, UK). Navigation errors were (1) distance error, the distance between the end target and a perpendicular line drawn from the sternum to the plane of targets, and (2) deviation, the angle formed between the line joining the initial and end targets and the line joining the subject's shoulders. RESULTS: Mean distance error was 20.9 +/- 22.0 degrees cm in patients, 29.6 +/- 30.3 cm in young healthy subjects, and -1.7 +/- 18.4 cm in older subjects (p < .01 compared with young subjects). Mean deviation was symmetric and 8 degrees and -3 degrees in healthy young and older subjects, respectively. In contrast, patients had a significantly larger deviation when navigating toward the side of their lesion than the intact side (13 degrees +/- 9 degrees versus 3 degrees +/- 9 degrees; p < .01). CONCLUSIONS: Our results suggest that patients with vestibular deficits have impaired ability to control body rotations when walking sideways without vision toward the side of their vestibular lesion.     

Relationships between the perception of nasalization and speech movements in speakers with cleft palate

The purpose of this study was to examine the relationships between several temporal measures of speech movements and perceived nasalization in speakers with cleft palate. Four adult subjects with repaired cleft palate were filmed using high-speed (100 frames/s) cinefluorography as they produced target syllables embedded in a carrier phrase. Perceived nasalization of each extracted acoustic target syllable was rated by 18 trained judges. Movements of the tongue tip, tongue dorsum, jaw, velar knee, velar tip, and posterior pharyngeal wall were plotted over time. Time of movement onsets and movement offsets was identified from the plots. Voice onset and offset times were identified from the synchronized acoustic recordings. The findings indicate that normally expected velopharyngeal movements occurred near the time of jaw-lowering onset during nasalized CVC and CVN productions in two subjects who were judged to exhibit high levels of nasalization. The other two subjects showed no velopharyngeal movements during the CVC production. It is speculated that velopharyngeal movements normally expected in CVC utterances may be avoided by some speakers with cleft palate in order to minimize perceptible nasalization.     

Sensorimotor aspects of high-speed artificial gravity: III. Sensorimotor adaptation

As a countermeasure to the debilitating physiological effects of weightlessness, astronauts could live continuously in an artificial gravity environment created by slow rotation of an entire spacecraft or be exposed to brief daily "doses" in a short radius centrifuge housed within a non-rotating spacecraft. A potential drawback to both approaches is that head movements made during rotation may be disorienting and nauseogenic. These side effects are more severe at higher rotation rates, especially upon first exposure. Head movements during rotation generate aberrant vestibular stimulation and Coriolis force perturbations of the head-neck motor system. This article reviews our progress toward distinguishing vestibular and motor factors in side effects of rotation, and presents new data concerning the rates of rotation up to which adaptation is possible. We have studied subjects pointing to targets during constant velocity rotation, because these movements generate Coriolis motor perturbations of the arm but do not involve unusual vestibular stimulation. Initially, reaching paths and endpoints are deviated in the direction of the transient lateral Coriolis forces generated. With practice, subjects soon move in straighter paths and land on target once more. If sight of the arm is permitted, adaptation is more rapid than in darkness. Initial arm movement trajectory and endpoint deviations are proportional to Coriolis force magnitude over a range of rotation speeds from 5 to 20 rpm, and there is rapid, complete motor adaptation at all speeds. These new results indicate that motor adaptation to high rotation rates is possible. Coriolis force perturbations of head movements also occur in a rotating environment but adaptation gradually develops over the course of many head movements.     

Aging effects upon smooth pursuit induced by step-ramp stimulation

OBJECTIVE: in predictable target movements, pursuit gains are extremely close to 1.0. Under these conditions, aging effects upon pursuit have not been detected. Step-ramp stimuli produced by unpredictable combinations would be favorable procedures to assess the properties of smooth pursuit between young and aged people. Methods: the target was a 0.5 degrees red laser spot. Eye movements of 49 normal subjects (26 younger subjects less than 49 years old and 23 older subjects more than 50 years old) were recorded with infrared reflection oculography and sampled at 250 Hz. Step direction and distance (2, 4, 6, 8 degrees) followed by 10 degrees /s ramp speed movement in the same (onward stimulus) or opposite to the direction (backward stimulus) were programmed in an unpredictable way before each set of ten tests. Both onward and backward stimulation were randomly given for each subject. Results: in the onward study, there was a close correlation between retinal slip velocity (RSV) and eye acceleration (EA), which was expressed as a regression curve, being steeper in the younger group. This means that the younger subjects could produce faster velocity and greater acceleration than the aged group (P<0.05). Conclusion: subtle reduction in visual acuity, visual fields and contrast sensitivity will be one of possible causes, and the degradation of cortical areas crucial for visual processing might be one of possible causes of slowing of pursuit EA.     

Cross-coupling in a body-translating reaction: interaural optokinetic stimulation reflects a gravitational cue

CONCLUSION: The velocity storage integrator does not play a dominant role in the postural response to vertical visual cues; more likely, retinal slip provides the main driving force. By contrast, sideways eye movement can drive the velocity storage integrator and preserve a gravitational cue, which would be observed as a cross-coupling effect on the postural response. OBJECTIVES: To investigate the mechanism by which optokinetic stimulation causes the body to translate and to determine whether the optokinetic information is accompanied by a gravitational cue, which would appear as a cross-coupling effect. MATERIALS AND METHODS: Directionally diverse optokinetic stimuli were presented to seven healthy subjects, with and without a fixation target, and the body-translation of the subjects was recorded. RESULTS: Horizontal optokinetic stimulation with a fixation target caused the body to translate in the same direction as the optic flow. Upward or downward vertical optokinetic stimulation caused the body to translate backward or forward, respectively, only when a fixation target was present. When the subject's interaural axis was parallel to the optokinetic flow, diagonal optokinetic stimulation in the absence of a fixation target elicited responses in the pitch plane similar to those elicited by vertical stimulation in the presence of a fixation target.     

Relationship between loudness discomfort level and acoustic reflex threshold for normal and sensorineural hearing-impaired individuals

The relationship between loudness discomfort level (LDL) and acoustic reflex threshold (ART) was determined by comparing the ART to the LDL obtained by the psychophysical method of constant stimuli. Randomly presented stimuli of 1000 Hz, 2000 Hz, and a multi-talker speech noise were presented to normal and sensorineural hearing-impaired listeners. The listener's task was to judge whether the stimulus was at a level that was: (1) too loud or uncomfortably loud; or (2) not too loud or not uncomfortably loud. Prior to the judgement of the subject acoustic reflex threshold were determined. Both LDL and ART were found to be significantly higher for the hearing-impaired group. For the pure tone stimuli, LDL for the hearing-impaired group was at or below the ART. Significant differences were shown to exist between LDL and ART for each group. A multiple regression analysis indicated significant correlations between LDL and ART. Ranges of prediction error were selected to investigate the ability of ART to predict LDL. Both pure tone and speech ART successfully predicted LDL within +/- 10 dB for a high percentage of the subjects.     

Visual acuity with noise and music at 107 dbA

In Exper. I, 10 normal-hearing college students performed visual acuity, visual search, and pursuit tracking tasks during music presented at 70 or 107 dbA. Only visual acuity was significantly worse during the higher sound level, which suggest that the effect existed at the relatively low level of sensory processing rather than at the level(s) of cognition and decision-making. In Exper. II, 28 similar Ss performed the visual acuity task during either music or noise presented at 70 or 107 dbA. Acuity was impaired by loud music but not by loud noise. It was suggested that the momentary peak levels in music may play a role in disrupting vestibulo-ocular control, and that some workplace noises may partake of this acoustic characteristic.     

Optimal parameters for the clinical test of dynamic visual acuity in patients with a unilateral vestibular deficit

OBJECTIVE: To determine the influence of frequency and direction of head movement and type of vision chart on the score of a clinical test of dynamic visual acuity (DVA). METHODS: The subjects were 31 healthy individuals (22 to 79 years old) and 10 patients (19 to 70 years old) with a unilateral vestibular deficit owing to surgical resection of an acoustic neuroma. They read a Snellen or an E-chart while their head was passively moved +/- 20 degrees back and forth in the horizontal or vertical direction at one of four frequencies (0.5, 1.0, 1.5, and 2.0 Hz). The DVA score was the difference in the number of lines on the vision chart that could be read with the head passively moved versus with the head immobile. RESULTS: Four healthy subjects had a low DVA score during horizontal head movements at the fastest frequency (2.0 Hz) with the Snellen chart. In patients, DVA scores significantly decreased as head movement frequency increased from 0.5 to 1.0 Hz and from 1.0 to 1.5 Hz, during horizontal and vertical movements, and with both vision charts (p < .001). The DVA scores of healthy subjects were more consistent across three trials with the E-chart than with the Snellen chart at 1.0 and 0.5 Hz (horizontal movements, p < .01) and at 1.5 and 1.0 Hz (vertical movements, p < .01). CONCLUSIONS: This study provides new indications on the optimal parameters for the clinical test of DVA. From the results, it is recommended that DVA be tested during horizontal and vertical head movements at a frequency of 1.5 Hz with the E-chart.     

Disturbances in the control of saccadic eye movement and eye-head coordination in schizophrenics.

Some schizophrenic patients have been known to have frontal cortical dysfunction. In view of the evidence that voluntary purposive eye movements and rapid head movements involve areas of the frontal cortex, investigations of saccade performance have been carried out on schizophrenics in various laboratories. We have compared performance of schizophrenic patients in tasks involving inhibition of reflexive saccades (no-saccade) and initiation of saccades without target (memory-saccade) with performance in the antisaccade task. These measures were also compared with results of eye-head coordination tasks. Schizophrenics showed more errors and significantly longer latencies, with lower peak velocities at large amplitudes, in both the antisaccade task and the memory-saccade task. Performance with coordinated eye-head movement was basically similar, except for significantly longer latencies of head movement. These results suggest that schizophrenics may have a disturbance in initiating and executing purposive saccades without targets, and that dysfunction of the frontal cortex may contribute to this disturbance.     

Acoustic responses of vestibular afferents in a model of superior canal dehiscence.

HYPOTHESIS: Afferents innervating the superior semicircular canal are rendered especially sensitive to acoustic stimulation when there is a dehiscence of the superior canal. Other vestibular end organs are also more sensitive to acoustic stimulation. BACKGROUND: Dehiscence of the superior semicircular canal is associated with vertigo and nystagmus caused by loud sounds (Tullio phenomenon) or changes in middle ear or intracranial pressures. The mechanisms by which acoustic stimuli act on the vestibular end organs are unclear. The nystagmus caused by acoustic stimuli generally aligns with the affected superior canal. METHODS: Responses to acoustic stimuli in the superior vestibular nerves of anesthetized chinchillas were recorded before and after fenestration of the superior canal. RESULTS: Two acoustic response patterns were seen: rapid phase locking and slow tonic changes in firing rate. Phasic responses principally occurred in irregular afferents and tonic responses in regular afferents. Afferents from all of the vestibular end organs encountered could respond to acoustic stimuli, even before fenestration. However, fenestration lowered the thresholds for acoustic stimulation in superior canal afferents with phasic responses and increased the magnitude of tonic responses. CONCLUSIONS: Superior canal dehiscence may render the irregular afferents innervating the superior canal particularly sensitive to loud sounds. Rapid phase-locking responses may explain the short latency of nystagmus seen in patients with superior canal dehiscence syndrome. The mechanisms by which acoustic stimuli activate the vestibular end organs may differ from the damped endolymph motion associated with head acceleration.     

Vestibulo-tactile interactions regarding motion perception and eye movements in yaw

This paper shows that tactile stimulation can override vestibular information regarding spinning sensations and eye movements. However, we conclude that the current data do not support the hypothesis that tactile stimulation controls eye movements directly. To this end, twenty-four subjects were passively disoriented by an abrupt stop after an increase in yaw velocity, about an Earth vertical axis, up to 120 degrees /s. Immediately thereafter, they had to actively maintain a stationary position despite a disturbance signal. Subjects wore a tactile display vest with 48 miniature vibrators, applied in different combinations with visual and vestibular stimuli. Their performance was quantified by RMS body velocity during self-control. Fast eye movement phases were analyzed by counting samples exceeding a velocity limit, slow phases by a novel method applying a first order model. Without tactile and visual information, subjects returned to a previous level of angular motion. Tactile stimulation decreased RMS self velocity considerably, though less than vision. No differences were observed between conditions in which the vest was active during the recovery phase only or during the disorienting phase as well. All effects of tactile stimulation found on the eye movement parameters could be explained by the vestibular stimulus.     

The plasticity of compensatory eye movements in bilateral vestibular loss. A study with low and high frequency rotatory tests

Twelve subjects with bilateral vestibular loss, with a mean age of 27 years (18-49) were studied. The loss was based on symptoms of oscillopsia and ice-water caloric tests. Nine subjects were evaluated by low-frequency sinusoidal harmonic acceleration (SHA) rotatory tests (0.01-0.32 Hz), and 3 subjects with high broad-frequency band rotatory tests (0.25-3.25 Hz). During alertness tests (darkness) all subjects had absent or very low gains. When tested with a stationary light in the middle of the swing, the SHA tests showed perfect compensatory eye movements with gains of 1 and phases of approximately 0 degrees. In the broad-frequency test, the gain was near 1 below 1 Hz, decreasing rapidly at higher frequencies. In imaginary stationary target tests (darkness), the gain was enhanced to 'normal' values (0.5) with a phase lead in the low-frequency range (SHA). This could not be replicated in the high-frequency tests. Testing with stationary acoustic guidance (darkness), further enhanced the gain in the SHA tests. A small increase of gain could also be found in the high-frequency tests. Compensatory eye movements, when tested in low-frequency rotatory tests (less than 1 Hz), are to a large extent influenced by non-vestibular mechanisms. By voluntary modifications, normal gains could be produced by patients with 'bilateral vestibular loss'. The phase lead found is proposed to be of central non-vestibular origin. Testing in higher frequency ranges (greater than 1 Hz) could not replicate these findings, thus the broad-frequency band rotatory test should be preferred for adequate vestibular quantification.     

Kinematic analyses of speech, orofacial nonspeech, and finger movements in stuttering and nonstuttering adults.

This work investigated the hypothesis that neuromotor differences between individuals who stutter and individuals who do not stutter are not limited to the movements involved in speech production. Kinematic data were obtained from gender- and age-matched stuttering (n = 10) and nonstuttering (n = 10) adults during speech movements, orofacial nonspeech movements, and finger movements. All movements were performed in 4 conditions differing in sequence length and location of the target movement within the sequence. Results revealed statistically significant differences between the stuttering and nonstuttering individuals on several measures of lip and jaw closing (but not opening) movements during perceptually fluent speech. The magnitude of these differences varied across different levels of utterance length (larger differences during shorter utterances) and across different locations of the target movement within an utterance (larger differences close to the beginning). Results further revealed statistically significant differences between the stuttering and nonstuttering groups in finger flexion (but not extension) movement duration and peak velocity latency. Overall, findings suggest that differences between stuttering and nonstuttering individuals are not confined to the sensorimotor processes underlying speech production or even movements of the orofacial system in general. Rather, it appears that the groups show generalized differences in the duration of certain goal-directed movements across unrelated motor systems.     

Effects of head orientation and lateral body tilt on egocentric coding: cognitive and sensory-motor accuracy

A major issue in motor control studies is to determine whether and how we use spatial frames of reference to organize our spatially oriented behaviors. In previous experiments we showed that simulated body tilt during off-axis rotation affected the performance in verbal localization and manual pointing tasks. It was hypothesized that the observed alterations were at least partly due to a change in the orientation of the egocentric frame of reference, which was indeed centered on the body but aligned with the gravitational vector. The present experiments were designed to test this hypothesis in a situation where no inertial constraints (except the usual gravitational one) exist and where the orientation of the body longitudinal z-axis was not aligned with the direction of the gravity. Eleven subjects were exposed to real static body tilt and were required to verbally localize (experiment 1) and to point as accurately as possible towards (experiment 2) memorized visual targets, in two conditions, Head-Free and Head-Fixed conditions. Results show that the performance was only affected by real body tilt in the localization task performed when the subject's head was tilted relative to the body. Thus, dissociation between gravity and body longitudinal z-axis alone is not responsible for localization nor for pointing errors. Therefore, the egocentric frame of reference seems independent from the orientation of the gravity with regard to body z-axis as expected from our previous studies. Moreover, the use of spatial referentials appears to be less mandatory than expected for pointing movements (motor task) than for localization task (cognitive task).     

Quantification of slow compensatory eye movements in patients with bilateral vestibular loss. A study with a broad frequency-band rotatory test

Seven patients with bilateral vestibular dysfunction were investigated with a new broad frequency oscillatory test. The vestibular stimulation was of two types: a pseudo-random oscillation in the frequency range 0.5-4 Hz and a sinusoidal frequency sweep from 0.5 to 3.5 Hz. Compensatory eye movements were recorded by EOG. Gain and phase values between eye and head movements were extracted using power spectral analysis technique. Two different visual conditions were used: 1) fixating a stationary target and /) fixating a moving target (visual suppression test). At high frequencies all patients showed a reduced VOR gain compared to normal subjects. At low frequencies gain values were close to normal when using a predictable (sinusoidal) stimulation. With a non-predictable (pseudo-random) stimulation gain values were significantly reduced even at low frequencies. The patients with the most severe loss showed a phase lag at higher frequencies (condition 1). The results in the oscillatory test were compared to subjective symptoms and caloric responses. The new test appears to be better suited to assess the vestibular function in patients with suspected bilateral vestibular loss than the caloric test or other traditional procedures.