Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “FEEDBACK”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44Linked to original sources
PubMed1999

Characteristics of visual feedback in postural control during standing.

In the present study, the visual feedback system in postural control was investigated. To suppress the vestibular and proprioceptive feedback paths, a subject stood on a force-measuring plate with a fixed back support. Because the subject's body was immovable under these conditions, the subject controlled a computer model which simulated body dynamics. Information on the sway angle of the model was fed visually. Under this condition, frequency response functions for the ankle moment in response to the sway angle were calculated. The experimental results suggest that the visual feedback system contains a large time delay and, consequently, the visual system does not by itself allow a subject to maintain an upright posture. Index Terms- Feedback control, frequency characteristics, identification, posture, visual sensory feedback.

Adult↗
PubMed2006

Corrective movements in response to displacements in visual feedback are more effective during periods of 13-35 Hz oscillatory synchrony in the human corticospinal system.

Oscillatory synchronization in the beta (approximately 20 Hz) band is a common feature of human motor control, manifest at cortical and muscular levels during tonic contraction. Here we test the hypothesis that the influence of visual feedback on performance in a positional hold task is increased during bursts of beta-band synchrony in the corticospinal motor system. Healthy subjects were instructed to extend their forefinger while receiving high-gain visual feedback of finger position on a PC screen. Small step displacements of the feedback signal were triggered either by bursts of beta oscillations in scalp electroencephalogram or randomly with respect to cortical beta activity, and the resulting positional corrections expressed as a percentage of the step displacement. Corrective responses to beta and randomly triggered step changes in visual feedback were 41.7+/-4.9 and 31.5+/-6.8%, respectively (P<0.05). A marked increase in the coherence in the beta band was also found between muscle activity and cortical activity during the beta-triggered condition. The results suggest that phasic elevations of beta activity in the corticospinal motor system are associated with an increase in the gain of the motor response to visual feedback during a tonic hold task. Beta activity may index a motor state in which processing relevant to the control of positional hold tasks is promoted, with behavioural consequences.

Adult↗
PubMed1975

False physiological feedback and persuasion: effect of fear arousal vs. fear reduction on attitude change.

Two experiments tested the hypothesis that increases in false physiological feedback of fear arousal will enhance persuasion and that reduction in the arousal feedback is unnecessary for increased persuasion to occur. Prior research has usually found a positive relation between level of arousal and persuasion, but support for the drive reduction hypothesis is tenuous. However, Harris and Jellison (1971) claimed support for such a hypothesis. They manipulated subjects' fear arousal cognitively via false physiological feedback while the subjects listened to a persuasive communication. The present experiments used a similar procedure in an attempt to test an "arousal only" against an "arousal reduction" hypothesis. Subjects listened to a persuasive speech while receiving false feedback via a meter concerning their fear arousal. In Experiment I half of the subjects received high arousal and half received moderate arousal information. Within each of these conditions half of the subjects had their arousal reduced, and the other half did not. In Experiment II subjects received either low arousal, high arousal, or high then low arousal feedback while listening. The results of the two studies generally provided support for the "arousal only" hypothesis. An interpretation in terms of Bem's attribution theory was tentatively suggested.

Arousal↗
PubMed1980

Video-feedback and personal attribution in anorexic, depressed and normal viewers.

Video-feedback has been shown to be particularly influential in changing bodily awareness and causal attribution by confronting participants with a concrete 'public' self-image. Body-image disturbance and denial are major aspects of patients suffering with anorexia nervosa. It was predicted that video-feedback should alter these attitudes in this group and result in a more realistic self-appraisal. Anorexics respond to video-feedback with a reduction in self-esteem whereas normal controls displayed an increase in self-esteem and depressed patients perceived themselves negatively both before and after video-feedback. It is concluded that video-feedback may prove to be a useful technique in the treatment of body-image disturbance in anorexic patients.

Adolescent↗
PubMed1991

Inhibition of tubuloglomerular feedback by the D1 agonist fenoldopam in chronically salt-loaded rats.

1. Chronic dietary NaCl loading in rats is paralleled by an increase of the dopamine concentration in the tubular fluid and humorally mediated inhibition of the tubuloglomerular feedback mechanism at the macula densa. Since these two phenomena are causally linked, the alterations in the tubuloglomerular feedback response by the luminal application of dopamine, the D1 agonist fenoldopam, the D2 agonist bromocriptine and the D1 and D2 antagonists SCH 23390 and metoclopramide were further investigated using the micropuncture technique. 2. Very similar, concentration-dependent inhibition of the tubuloglomerular feedback response was observed for dopamine and fenoldopam. Half-maximal inhibition was achieved at 10(-11) M and the slope factors of the sigmoid concentration-response curves were comparable. Bromocriptine was ineffective. 3. The inhibition of TGF by both agonists could be antagonized very similarly and concentration dependently by the D1 antagonist SCH 23390. At equimolar concentrations of 10(-9) M the inhibition was reduced by approximately 50%. Raising the SCH 23390 concentration to 10(-6) M completely abolished the TGF inhibition. In contrast, TGF inhibition by 10(-9) M-fenoldopam or dopamine was not significantly affected by an equimolar concentration of the D2 antagonist metoclopramide. Increasing metoclopramide concentration to 10(-6) M attenuated tubuloglomerular feedback inhibition by approximately 55%. 4. It is concluded that the inhibition of tubuloglomerular feedback seen during chronic dietary salt loading can be ascribed to the binding of endogenous dopamine to luminal D1 receptors on the macula densa cells.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed2000

Perceptual calibration of F0 production: evidence from feedback perturbation.

Hearing one's own speech is important for language learning and maintenance of accurate articulation. For example, people with postlinguistically acquired deafness often show a gradual deterioration of many aspects of speech production. In this manuscript, data are presented that address the role played by acoustic feedback in the control of voice fundamental frequency (F0). Eighteen subjects produced vowels under a control (normal F0 feedback) and two experimental conditions: F0 shifted up and F0 shifted down. In each experimental condition subjects produced vowels during a training period in which their F0 was slowly shifted without their awareness. Following this exposure to transformed F0, their acoustic feedback was returned to normal. Two effects were observed. Subjects compensated for the change in F0 and showed negative aftereffects. When F0 feedback was returned to normal, the subjects modified their produced F0 in the opposite direction to the shift. The results suggest that fundamental frequency is controlled using auditory feedback and with reference to an internal pitch representation. This is consistent with current work on internal models of speech motor control.

Acoustics↗
PubMed2002

Active vibroacoustic control with multiple local feedback loops.

When multiple actuators and sensors are used to control the vibration of a panel, or its sound radiation, they are usually positioned so that they couple into specific modes and are all connected together with a centralized control system. This paper investigates the physical effects of having a regular array of actuator and sensor pairs that are connected only by local feedback loops. An array of 4 x 4 force actuators and velocity sensors is first simulated, for which such a decentralized controller can be shown to be unconditionally stable. Significant reductions in both the kinetic energy of the panel and in its radiated sound power can be obtained for an optimal value of feedback gain, although higher values of feedback gain can induce extra resonances in the system and degrade the performance. A more practical transducer pair, consisting of a piezoelectric actuator and velocity sensor, is also investigated and the simulations suggest that a decentralized controller with this arrangement is also stable over a wide range of feedback gains. The resulting reductions in kinetic energy and sound power are not as great as with the force actuators, due to the extra resonances being more prominent and at lower frequencies, but are still worthwhile. This suggests that an array of independent modular systems, each of which included an actuator, a sensor, and a local feedback control loop, could be a simple and robust method of controlling broadband sound transmission when integrated into a panel.

Acoustics↗
PubMed2006

The Foundation Programme assessment tools: an opportunity to enhance feedback to trainees?

The recent change in working patterns of doctors in training has meant that the traditional systems of education are under increasing pressure and that there is the need to maximise new opportunities for learning. One new opportunity may arise after the introduction of the mandatory assessment systems (Mini-CEX, DOPPS, Multi-source feedback, and Case based discussion) in the Foundation Programmes. In this review the new assessment procedures for the Foundation Programmes are outlined and the potential of these assessments (using Mini-CEX as main example) as an opportunity to give feedback to trainees discussed. The importance of feedback in professional development and some of the techniques available for giving feedback are described. The Foundation Programme assessments will occupy a significant amount of trainees' and trainers' time and it is important that opportunity for feedback and learning is maximised.

Curriculum↗
PubMed2001

Feedback of patients' evaluations of general practice care: a randomised trial.

OBJECTIVE: To assess the effects of feedback of patients' evaluations of care to general practitioners. DESIGN: Randomised trial. SETTING: General practice in the Netherlands. SUBJECTS: 55 GPs and samples of 3691 and 3595 adult patients before and after the intervention, respectively. INTERVENTIONS: GPs in the intervention group were given an individualised structured feedback report concerning evaluations of care provided by their own patients. Reference figures referring to other GPs were added as well as suggestions for interpretation of this feedback, an evidence-based overview of factors determining patients' evaluations of care, and methods to discuss and plan improvements. MAIN OUTCOME MEASURES: Patients' evaluations of nine dimensions of general practice measured with the CEP, a previously validated questionnaire consisting of 64 questions, using a six point answering scale (1= poor, 6 = very good). RESULTS: Mean scores per CEP dimension varied from 3.88 to 4.77. Multilevel regression analysis showed that, after correction for baseline scores, patients' evaluations of continuity and medical care were less positive after the intervention in the intervention group (4.60 v 4.77, p < 0.05 and 4.68 v 4.71, p < 0.05, respectively). No differences were found in the remaining seven CEP dimensions. CONCLUSIONS: Providing feedback on patients' evaluations of care to GPs did not result in changes in their evaluation of the care received. This conclusion challenges the relevance of feedback on patients' evaluations of care for quality improvement.

Adult↗
PubMedDate not supplied

Contribution of sensory feedback to ongoing ankle extensor activity during the stance phase of walking.

Numerous investigations over the past 15 years have demonstrated that sensory feedback plays a critical role in establishing the timing and magnitude of muscle activity during walking. Here we review recent studies reporting that sensory feedback makes a substantial contribution to the activation of extensor motoneurons during the stance phase. Quantitative analysis of the effects of loading and unloading ankle extensor muscles during walking on a horizontal surface has shown that sensory feedback can increase the activity of ankle extensor muscles by up to 60%. There is currently some uncertainty about which sensory receptors are responsible for this enhancement of extensor activity, but likely candidates are the secondary spindle endings in the ankle extensors of humans and the Golgi tendon organs in the ankle extensors of humans and cats. Two important issues arise from the finding that sensory feedback from the leg regulates the magnitude of extensor activity. The first is the extent to which differences in the magnitude of activity in extensor muscles during different locomotor tasks can be directly attributed to changes in the magnitude of sensory signals, and the second is whether the enhancement of extensor activity is determined primarily by feedback from a specific group of receptors or from numerous groups of receptors distributed throughout the leg. Limitations of current experimental strategies prevent a straightforward empirical resolution of these issues. A potentially fruitful approach in the immediate future is to develop models of the known and hypothesized neuronal networks controlling motoneuronal activity, and use these simulations to control forward dynamic models of the musculo-skeletal system. These simulations would help understand how sensory signals are modified with a change in locomotor task and, in conjunction with physiological experiments, establish the extent to which these modifications can account for changes in the magnitude of motoneuronal activity.

Animals↗
PubMed1983

The effect of tubular perfusion with PGE2, PGF2 alpha, and PGI2 on the tubuloglomerular feedback control in the rat.

The prostaglandins (PG) of the renal medulla might affect the nephron and the cortical arteriolar function via the tubular route. To investigate this question PGE2 (1 microgram/mL), PGF2 alpha (10 micrograms/mL), or PGI2 (1 ng/mL) was added to the tubular perfusion solution when the characteristics of the tubuloglomerular feedback (TGF) control were measured. The experiments were performed on Sprague-Dawley rats. The proximal tubular stop-flow pressure (PSF) was measured upstream to a wax block, while at the same time the distal nephron was perfused with prostaglandin-containing or prostaglandin-free solutions at different flow rates varying from 0 to 50 nL/min. The maximal drop in PSF (delta PSF) and the tubular flow rate at which 50% of the delta PSF response was obtained, the turning point (TP), were determined. When PGE2 or PGF2 alpha was added to the tubular perfusion solution in the control animals a significant increase in feedback sensitivity was found. After 10 min of tubular PGI2 perfusion the feedback sensitivity was almost completely abolished, with a delta PSF of 0.8 mmHg (1 mmHg = 133.322 Pa) (control 8.4 mmHg) and a TP of greater than 40 nL/min (control 22 nL/min). After nephrectomy the feedback sensitivity was reduced, with a delta PSF of 2.0 mmHg and a TP of greater than 40 nL/min. When PGE2 was added to the tubular perfusion solution in the uninephrectomized animals, the feedback sensitivity was increased to the control level, with a delta PSF of 8.2 mmHg and a TP of 20.0 nL/min.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1977

Control of extracellular sodium concentration by antidiuretic hormone-thirst feedback mechanism.

The effectiveness of the antidiuretic hormone (ADH)-thirst feedback mechanism to control extracellular sodium concentration was studied in dogs. The design consisted of increasing daily sodium intake from 10 to 200 meq in a group of dogs, first in the normal condition and second with a continuous 24 h/day infusion of an amount of ADH sufficient to maintain urine osmolarity at a maximal level and with fixed water intake. We were therefore able to compare the effectiveness of sodium concentration control in the same dogs with and without feedback control of the ADH-thirst mechanism, the difference in effectiveness being a quantitative measure of the control capability of the system. In the normal condition the increase in sodium intake resulted in a steady-state 2.3% elevation in sodium concentration. With the feedback control of ADH secretion and water intake blocked, the same sodium forcing produced an 11.9% increase in extracellular sodium concentration. The minimum feedback gain for the system calculated from the data is -4.2. We conclude that control of sodium concentration in the intact state is accomplished mainly by the ADH-thirst feedback mechanism.

Animals↗
PubMed1997

Role of pulmonary stretch receptor feedback in control of episodic breathing in the bullfrog.

This study compared the "fictive" breathing patterns of decerebrate, paralyzed, unidirectionally ventilated bullfrogs in which pulmonary stretch receptor (PSR) feedback was either absent bilateral vagotomy), maintained constant at different levels (tonic) or oscillated with each fictive breath (phasic) under different levels of hypoxic or CO2-related respiratory drive. Tonic and phasic PSR feedback had identical effects on the fictive breathing pattern; decreasing PSR feedback increased the peak integrated trigeminal electroneurogram recordings and decreased breathing frequency. The effects of bilateral vagotomy and lung deflation to 0 cmH2O on breathing pattern were identical. Although hypoxia (fractional concentration of O2 in air = 0.06) had no significant effect on fictive breathing, ventilating frogs with increasing CO2 levels (fractional CO2 concentration in inspired air range: 0.00-0.03) increased the number of breaths in each fictive breathing episode, and this effect was potentiated by PSR feedback. Whenever respiratory drive was increased, regardless of the method (increase in PSR feedback or chemoreceptor drive), occasional single breaths were replaced by breathing episodes, indicating that the mechanisms responsible for the clustering of the breaths and the onset/termination of breathing episodes are not dependent on either input alone.

Animals↗
PubMed2001

Secretory process regularity monitors neuroendocrine feedback and feedforward signaling strength in humans.

The present experiments examine the neuroregulatory hypothesis that the degree of sample-by-sample regularity of hormone output by an interlinked hypothalamopituitary target-organ system monitors the strength of feedback and/or feedforward signaling. To test this postulate and assess its generality, we implemented a total of nine thematically complementary perturbation experiments. In particular, we altered feedback or feedforward signaling selectively in two distinct neuroendocrine systems; namely, the growth hormone (GH) insulin-like growth factor type I (IGF-I) and the luteinizing hormone-testosterone axes. Four experimental paradigms comprised preferential reduction vs. enhancement of IGF-I or testosterone feedback signal strength; and, conversely, five others entailed selective attenuation vs. augmentation of GH-releasing hormone and gonadotropin-releasing hormone feedforward signal intensity. In these independent interventions, quantitation of subordinate (nonpulsatile) secretory pattern reproducibility via the approximate entropy statistic unmasked salient changes (P values typically <10(-3)) in the conditional regularity of serial hormone output with high consistency (96-100%). In particular, approximate entropy quantified degradation of secretory subpattern orderliness under either muted feedback restraint or heightened feedforward drive. Assuming valid interpretation of the biological constraints imposed, these experimental observations coincide with earlier reductionist mathematical predictions, wherein increased irregularity of coupled parameter output mirrors attenuated feedback and/or augmented feedforward coupling within an integrative system.

Fasting↗
PubMed2002

Evidence that the superior colliculus participates in the feedback control of saccadic eye movements.

There is general agreement that saccades are guided to their targets by means of a motor error signal, which is produced by a local feedback circuit that calculates the difference between desired saccadic amplitude and an internal copy of actual saccadic amplitude. Although the superior colliculus (SC) is thought to provide the desired saccadic amplitude signal, it is unclear whether the SC resides in the feedback loop. To test this possibility, we injected muscimol into the brain stem region containing omnipause neurons (OPNs) to slow saccades and then determined whether the firing of neurons at different sites in the SC was altered. In 14 experiments, we produced saccadic slowing while simultaneously recording the activity of a single SC neuron. Eleven of the 14 neurons were saccade-related burst neurons (SRBNs), which discharged their most vigorous burst for saccades with an optimal amplitude and direction (optimal vector). The optimal directions for the 11 SRBNs ranged from nearly horizontal to nearly vertical, with optimal amplitudes between 4 and 17 degrees. Although muscimol injections into the OPN region produced little change in the optimal vector, they did increase mean saccade duration by 25 to 192.8% and decrease mean saccade peak velocity by 20.5 to 69.8%. For optimal vector saccades, both the acceleration and deceleration phases increased in duration. However, during 10 of 14 experiments, the duration of deceleration increased as fast as or faster than that of acceleration as saccade duration increased, indicating that most of the increase in duration occurred during the deceleration phase. SRBNs in the SC changed their burst duration and firing rate concomitantly with changes in saccadic duration and velocity, respectively. All SRBNs showed a robust increase in burst duration as saccadic duration increased. Five of 11 SRBNs also exhibited a decrease in burst peak firing rate as saccadic velocity decreased. On average across the neurons, the number of spikes in the burst was constant. There was no consistent change in the discharge of the three SC neurons that did not exhibit bursts with saccades. Our data show that the SC receives feedback from downstream saccade-related neurons about the ongoing saccades. However, the changes in SC firing produced in our study do not suggest that the feedback is involved with producing motor error. Instead, the feedback seems to be involved with regulating the duration of the discharge of SRBNs so that the desired saccadic amplitude signal remains present throughout the saccade.

Action Potentials↗
PubMed2003

Spindle model responsive to mixed fusimotor inputs and testable predictions of beta feedback effects.

Skeletofusimotor (beta) motoneurons innervate both extrafusal muscle units and muscle fibers within muscle spindle stretch receptors. By receiving excitation from group Ia muscle spindle afferents and driving the muscle spindle afferents that excite them, they form a positive feedback loop of unknown function. To study it, we developed a computationally efficient model of group Ia afferent behavior, capable of responding to multiple fusimotor inputs, that matched experimental data. This spindle model was then incorporated into a simulation of group Ia feedback during ramp/hold and triangular stretches with and without closure of the beta loop, assuming that gamma and beta fusimotor drives of the same type (static or dynamic) have identical effects on spindle afferent firing. The effects of beta feedback were implemented by driving a fusimotor input with a delayed and filtered fraction of the spindle afferent output. During triangular stretches, feedback through static beta motoneurons enhanced Ia afferent firing during shortening of the spindle. In contrast, closure of a dynamic beta loop increased Ia firing during lengthening. The strength of beta feedback, estimated as a "loop gain" was comparable to experimental estimates. The loop gain increased with velocity and amplitude of stretch but decreased with increased superimposed gamma fusimotor rates. The strongest loop gains were seen when the beta loop and the gamma bias were of different types (static vs. dynamic).

Algorithms↗
PubMed2002

Positive proprioceptive feedback elicited by isometric contractions of ankle flexors on pretibial motoneurons in cats.

Pretibial flexor motoneurons were recorded intracellularly in anesthetized cats during unfused isometric contractions of a subpopulation of motor units from either tibialis anterior (TA) or extensor digitorum longus (EDL) muscles. The contractions elicited excitatory postsynaptic potentials in 23 of 28 pretibial flexor motoneurons. No effect was observed in the remaining motoneurons. In control experiments, the effects of electrical stimulation of afferents within the TA nerve were investigated to help identify afferents responsible for the contraction-induced positive feedback. This feedback was ascribed to actions of Ia fibers because the pattern of the contraction-induced excitatory potentials was consistent with the known pattern of Ia discharge; in control experiments, electrical stimulation of group I fibers elicited only monosynaptic excitatory potentials; and the distribution of both the contraction-induced positive feedback among motor nuclei as well as the electrically evoked Ia excitatory monosynaptic potentials were restricted to homonymous and synergic motoneurons. Observation of the Ia contraction-induced positive feedback was facilitated by the absence of Ib autogenic inhibition. This contraction-induced Ia excitatory feedback in ankle flexors might either reinforce Ia-induced reflexes when these muscles are lengthened or help to lift the leg over an obstacle.

Anesthesia↗
PubMed2005

Recurrent feedback in the mormyrid electrosensory system: cells of the preeminential and lateral toral nuclei.

Many sensory regions integrate information ascending from peripheral receptors with descending inputs from other central structures. However, the significance of these descending inputs remains poorly understood. Descending inputs are prominent in the electrosensory system of mormyrid fish and include both recurrent connections from higher to lower stages of electrosensory processing and electric organ corollary discharge (EOCD) signals associated with the motor command that drives the electric organ discharge. The preeminential nucleus (PE) occupies a key position in a feedback loop that returns information from higher stages of electrosensory processing to the initial stage of processing in the electrosensory lobe (ELL). This feedback reflects the integration of ascending electrosensory input from ELL, descending input from the lateral toral nucleus (torus), and EOCD inputs to PE. We used intracellular recording and axonal tracing of stained cells to characterize EOCD and electrosensory responses of several cell types in PE and the torus. PE and toral cells exhibit prominent EOCD responses that are not due to EOCD inputs from ELL. PE cells giving rise to a direct feedback projection to ELL respond to electrosensory stimuli with rapid, precisely timed spikes that will affect ELL neurons early during the same EOD cycle. EOCD and electrosensory responses in toral cells are similar to those observed in PE and may be important in shaping feedback to ELL. These results provide an initial description of electrosensory feedback to ELL as well as information about how ascending, descending, and EOCD inputs are combined at higher stages of electrosensory processing.

Action Potentials↗