scholarly journals Role of Visual Feedback in Upright Posture Control

2001 ◽  
Vol 13 (6) ◽  
pp. 594-600 ◽  
Author(s):  
Takanobu Nagata ◽  
◽  
Akimasa Ishida ◽  
Yutaka Fukuoka ◽  
Haruyuki Minamitani ◽  
...  
Keyword(s):  
Visual System ◽  
Visual Feedback ◽  
Sagittal Plane ◽  
Low Frequency ◽  
Posture Control ◽  
Body Sway ◽  
Upright Posture ◽  
Frequency Range ◽  
Short Term

We studied the role of visual feedback in upright posture control on the sagittal plane. In posture control, each sensory system has the following roles: initial detection of sway, suppression of short-term sway around the equilibrium point, and suppression of longterm sway induced by a slow shift in equilibrium. Experiments were conducted to examine features of each sensor and then visual contribution was studied. Based on measured sensory thresholds for the perception of sway during standing, it was suggested that visual input provided sensitive means of perceiving postural sway. Body sway of a subject was measured under several conditions in which the subject controlled upright posture utilizing the definite number of sensors. By analyzing and comparing measured sway waveforms under each condition, it was clear that the visual system suppressed short-term sway. Spectral analysis showed that the visual system suppressed body sway in a low frequency range around 0.2 Hz. Though visual feedback contains a large time delay, the influence of the delay is small in the low frequency range. It is rational that vision is efficient at suppressing body sway in the low frequency range.

Vestibulo-Ocular (VOR) Abnormalities at High Rotational Frequencies in Patients with Meniere' Disease

1988 ◽  
Vol 98 (3) ◽  
pp. 211-214 ◽  
Author(s):  
V.S. Dayal ◽  
M. Mai ◽  
R.D. Tomlinson
Keyword(s):  
Visual Feedback ◽  
Low Frequency ◽  
Normal Subjects ◽  
Steady Increase ◽  
Apparent Difference ◽  
Rapid Rise ◽  
Frequency Range ◽  
Meniere Disease ◽  
High Frequencies ◽  
Gaze Stability

Although visual feedback is required to maintain gaze stability during low-frequency rotations (below 1 Hz) because of suboptimal VOR gain in this frequency range, such behavior is not as evident at higher frequencies. Benson1 and Hydén et al.2 noted a steady increase in VOR gain in the higher-frequency range (2 to 5 Hz), where visual feedback has little effect. Similar behavior has also been reported in the monkey models. Eleven patients with diagnoses of Meniere's disease had tests of VOR and VOR cancellations performed with the use of pseudorandom oscillations as high as 5 Hz. The reponses at various frequencies were compared with normal data from 17 subjects. The VOR gain in patients exhibited a more rapid rise at high frequencies than that observed in normal subjects. For example, at 3.5 Hz the normal gain was 1.09, whereas patients exhibited a gain of 1.35 (mean of 11 subjects). When the performance during VOR cancellation tasks was compared, Meniere's patients appeared to be less able to perform these tasks; however, when the values were compared by use of a cancellation index that compensates for any difference in VOR gain, this apparent difference disappeared.

Autonomic cardiovascular regulation in subjects with acute mountain sickness

2005 ◽  
Vol 289 (6) ◽  
pp. H2364-H2372 ◽  
Author(s):  
Paola A. Lanfranchi ◽  
Roberto Colombo ◽  
George Cremona ◽  
Paolo Baderna ◽  
Liliana Spagnolatti ◽  
...  
Keyword(s):  
High Altitude ◽  
Potential Role ◽  
Acute Mountain Sickness ◽  
Low Frequency ◽  
Short Term ◽  
Mountain Sickness ◽  
Low Altitude ◽  
Normalized Units ◽  
Hypoxic Gas Mixture

The aims of this study were 1) to evaluate whether subjects suffering from acute mountain sickness (AMS) during exposure to high altitude have signs of autonomic dysfunction and 2) to verify whether autonomic variables at low altitude may identify subjects who are prone to develop AMS. Forty-one mountaineers were studied at 4,559-m altitude. AMS was diagnosed using the Lake Louise score, and autonomic cardiovascular function was explored using spectral analysis of R-R interval and blood pressure (BP) variability on 10-min resting recordings. Seventeen subjects (41%) had AMS. Subjects with AMS were older than those without AMS ( P < 0.01). At high altitude, the low-frequency (LF) component of systolic BP variability (LFSBP) was higher ( P = 0.02) and the LF component of R-R variability in normalized units (LFRRNU) was lower ( P = 0.001) in subjects with AMS. After 3 mo, 21 subjects (43% with AMS) repeated the evaluation at low altitude at rest and in response to a hypoxic gas mixture. LFRRNU was similar in the two groups at baseline and during hypoxia at low altitude but increased only in subjects without AMS at high altitude ( P < 0.001) and did not change between low and high altitude in subjects with AMS. Conversely, LFSBP increased significantly during short-term hypoxia only in subjects with AMS, who also had higher resting BP ( P < 0.05) than those without AMS. Autonomic cardiovascular dysfunction accompanies AMS. Marked LFSBP response to short-term hypoxia identifies AMS-prone subjects, supporting the potential role of an exaggerated individual chemoreflex vasoconstrictive response to hypoxia in the genesis of AMS.

scholarly journals Physical Validation of a Residual Impedance Rejection Method during Ultra-Low Frequency Bio-Impedance Spectral Measurements

Sensors ◽  
2020 ◽  
Vol 20 (17) ◽  
pp. 4686
Author(s):  
Zoltan Vizvari ◽  
Nina Gyorfi ◽  
Akos Odry ◽  
Zoltan Sari ◽  
Mihaly Klincsik ◽  
...  
Keyword(s):  
Measurement Errors ◽  
State Of The Art ◽  
Research Work ◽  
Low Frequency ◽  
Impedance Spectrum ◽  
Frequency Range ◽  
System Characterization ◽  
Art Methods ◽  
Measuring Frequency

Accurate and reliable measurement of the electrical impedance spectrum is an essential requirement in order to draw relevant conclusions in many fields and a variety of applications; in particular, for biological processes. Even in the state-of-the-art methods developed for this purpose, the accuracy and efficacy of impedance measurements are reduced in biological systems, due to the regular occurrence of parameters causing measurement errors such as residual impedance, parasitic capacitance, generator anomalies, and so on. Recent observations have reported the necessity of decreasing such inaccuracies whenever measurements are performed in the ultra-low frequency range, as the above-mentioned errors are almost entirely absent in such cases. The current research work proposes a method which can reject the anomalies listed above when measuring in the ultra-low frequency range, facilitating data collection at the same time. To demonstrate our hypothesis, originating from the consideration of the determinant role of the measuring frequency, a physical model is proposed to examine the effectiveness of our method by measuring across the commonly used vs. ultra-low frequency ranges. Validation measurements reflect that the range of frequencies and the accuracy is much greater than in state-of-the-art methods. Using the proposed new impedance examination technique, biological system characterization can be carried out more accurately.

Role of carotid sinus baroreflex in attenuating systemic arterial pressure variability studied in anesthetized dogs

1994 ◽  
Vol 266 (2) ◽  
pp. H720-H729 ◽  
Author(s):  
T. Yoshida ◽  
Y. Harasawa ◽  
T. Kubota ◽  
H. Chishaki ◽  
T. Kubo ◽  
...  
Keyword(s):  
Arterial Pressure ◽  
Carotid Sinus ◽  
Amplitude Spectrum ◽  
Low Frequency ◽  
Systemic Arterial Pressure ◽  
Open Loop ◽  
Frequency Range ◽  
Carotid Sinus Baroreflex ◽  
Anesthetized Dogs

Attenuation of systemic arterial pressure (SAP) variability by the carotid sinus baroreflex (CSBR) was quantified in nine anesthetized, vagotomized dogs. SAP amplitude spectrum was compared between open-loop [SAPo(f)] and closed-loop [SAPc(f)] operation of the CSBR. At 0.002 Hz, SAPc amplitude was 3.5 +/- 2.2 (SD) mmHg, and SAPo was 9.6 +/- 3.5 mmHg (P < 0.01). At 0.02 Hz, SAP(c) amplitude was 2.8 +/- 1.2 mmHg, and SAPo was 4.3 +/- 1.2 mmHg (P < 0.05). At higher frequencies, SAPo(f) was indistinguishable from SAPc(f). With the opened CSBR, intracarotid sinus pressure (CSP) was pseudorandomly varied, and the resulting SAP responses were recorded to determine the transfer function from CSP to SAP [HCSP.SAP(f)]. From SAPo(f) and the determined HCSP.SAP(f), we estimated SAP(f) if the CSBR was closed [SAPc,est(f)] and compared it with SAPc(f). These two spectra were similar in each dog over a frequency range of 0.002–0.15 Hz, the differences between SAPo(f) and SAPc(f) being reconcilable with HCSP.SAP(f). Although the anesthetized state and vagotomy may have distorted the transfer characteristics of the CSBR from those in conscious (with the intact vagi) states, the results of the present study indicate that the CSBR attenuated SAP variability mainly in a low-frequency range below 0.02 Hz and that this attenuation was attributable to the transfer properties of the CSBR.

scholarly journals Trunk stabilization during sagittal pelvic tilt: from trunk-on-pelvis to trunk-in-space due to vestibular and visual feedback

2016 ◽  
Vol 115 (3) ◽  
pp. 1381-1388 ◽  
Author(s):  
Paul van Drunen ◽  
Frans C. T. van der Helm ◽  
Jaap H. van Dieën ◽  
Riender Happee
Keyword(s):  
Visual Feedback ◽  
Pelvic Tilt ◽  
Sagittal Plane ◽  
Task Instruction ◽  
Body Sway ◽  
Low Back ◽  
Flexion Extension ◽  
Trunk Sway ◽  
Eyes Open ◽  
Trunk Stabilization

The goal of this study was to investigate the human ability to stabilize the trunk in space during pelvic tilt. Upper body sway was evoked in kneeling-seated healthy subjects by angular platform perturbations with a rotation around a virtual low-back pivot point between the L4 and L5 vertebrae. To investigate motor control modulation, variations in task instruction (balance naturally or minimize trunk sway), vision (eyes open or closed), and perturbation bandwidth (from 0.2 up to 1, 3, or 10 Hz) were applied. Cocontraction and proprioceptive muscle spindle feedback were associated with minimizing low-back flexion/extension (trunk-on-pelvis stabilization), while vestibular and visual feedback were supposed to contribute to trunk-in-space stabilization. Trunk-in-space stabilization was only observed with the minimize trunk sway task instruction, while the task instruction to balance naturally led to trunk-on-pelvis stabilization with trunk rotations even exceeding the perturbations. This indicates that vestibular feedback is used when minimizing trunk sway but has only a minor contribution during natural trunk stabilization in the sagittal plane. The eyes open condition resulted in reduced global trunk rotations and increased global trunk reflexive responses, demonstrating effective visual contributions to trunk-in-space stabilization. On the other hand, increasing perturbation bandwidth caused a decreased feedback contribution leading to deteriorated trunk-in-space stabilization.

The role of central vasopressin receptors in the modulation of autonomic cardiovascular controls: a spectral analysis study

2006 ◽  
Vol 291 (6) ◽  
pp. R1579-R1591 ◽  
Author(s):  
Sanja Milutinović ◽  
David Murphy ◽  
Nina Japundžić-Žigon
Keyword(s):  
Blood Pressure ◽  
Spectral Analysis ◽  
Low Frequency ◽  
Systolic Arterial Pressure ◽  
Short Term ◽  
Vasopressin Receptors ◽  
The Central Nervous System ◽  
Respiratory Stimulation ◽  
Stimulation Of

Although it has been suggested that vasopressin (VP) acts within the central nervous system to modulate autonomic cardiovascular controls, the mechanisms involved are not understood. Using nonpeptide, selective V1a, V1b, and V2 antagonists, in conscious rats, we assessed the roles of central VP receptors, under basal conditions, after the central application of exogenous VP, and after immobilization, on cardiovascular short-term variability. Equidistant sampling of blood pressure (BP) and heart rate (HR) at 20 Hz allowed direct spectral analysis in very-low frequency (VLF-BP), low-frequency (LF-BP), and high-frequency (HF-BP) blood pressure domains. The effect of VP antagonists and of exogenous VP on body temperature (Tb) was also investigated. Under basal conditions, V1a antagonist increased HF-BP and Tb, and this was prevented by metamizol. V1b antagonist enhanced HF-BP without affecting Tb, and V2 antagonist increased VLF-BP variability which could be prevented by quinapril. Immobilization increased BP, LF-BP, HF-BP, and HF-HR variability. V1a antagonist prevented BP and HR variability changes induced by immobilization and potentiated tachycardia. V1b antagonist prevented BP but not HR variability changes, whereas V2 antagonist had no effect. Exogenous VP increased systolic arterial pressure (SAP) and HF-SAP variability, and this was prevented by V1a and V1b but not V2 antagonist pretreatment. Our results suggest that, under basal conditions, VP, by stimulation of V1a, V1b, and cognate V2 receptors, buffers BP variability, mostly due to thermoregulation. Immobilization and exogenous VP, by stimulation of V1a or V1b, but not V2 receptors, increases BP variability, revealing cardiorespiratory adjustment to stress and respiratory stimulation, respectively.

Estimated Cochlear Delays in Low Best-Frequency Neurons in the Barn Owl Cannot Explain Coding of Interaural Time Difference

2010 ◽  
Vol 104 (4) ◽  
pp. 1946-1954 ◽  
Author(s):  
Martin Singheiser ◽  
Brian J. Fischer ◽  
Hermann Wagner
Keyword(s):  
Interaural Time Difference ◽  
Low Frequency ◽  
Barn Owl ◽  
Time Difference ◽  
Central Nucleus ◽  
Response Functions ◽  
Frequency Range ◽  
Response Peak ◽  
Cochlear Delays

The functional role of the low-frequency range (<3 kHz) in barn owl hearing is not well understood. Here, it was tested whether cochlear delays could explain the representation of interaural time difference (ITD) in this frequency range. Recordings were obtained from neurons in the core of the central nucleus of the inferior colliculus. The response of these neurons varied with the ITD of the stimulus. The response peak shared by all neurons in a dorsoventral penetration was called the array-specific ITD and served as criterion for the representation of a given ITD in a neuron. Array-specific ITDs were widely distributed. Isolevel frequency response functions obtained with binaural, contralateral, and ispilateral stimulation exhibited a clear response peak and the accompanying frequency was called the best frequency. The data were tested with respect to predictions of a model, the stereausis model, assuming cochlear delays as source for the best ITD of a neuron. According to this model, different cochlear delays determined by mismatches between the ipsilateral and contralateral best frequencies are the source for the ITD in a binaural neuron. The mismatch should depend on the best frequency and the best ITD. The predictions of the stereausis model were not fulfilled in the low best-frequency neurons analyzed here. It is concluded that cochlear delays are not responsible for the representation of best ITD in the barn owl.

Evaluation of Special Hearing Aids for Deaf Children

1971 ◽  
Vol 36 (4) ◽  
pp. 527-537 ◽  
Author(s):  
Norman P. Erber
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Hearing Aid ◽  
Low Frequency ◽  
Acoustic Stimulation ◽  
Deaf Children ◽  
Frequency Range ◽  
Frequency Limit ◽  
Unpublished Studies ◽  
Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

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