Mechanism of feedback inhibition by leucine. Purification and properties of a feedback-resistant alpha-isopropylmalate synthase.
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Dimethyl Suberimidate↗
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The effects of feedback sensory modality, feedback information content, and sex on short-term biofeedback training of three responses.
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Adolescent↗
The choice of feedback stimulus can determine the success of alpha feedback training.
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Acoustic Stimulation↗
Feedback on a feedback loop: the hypothalamic-pituitary-gonadal axis.
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Amyloid beta-Peptides↗
Student feedback in problem based learning: a survey of 103 final year students across five Ontario medical schools.
CONTEXT: Problem based learning (PBL) has become an integral component of medical curricula around the world. In Ontario, Canada, PBL has been implemented in all five Ontario medical schools for several years. Although proper and timely feedback is an essential component of medical education, the types of feedback that students receive in PBL have not been systematically investigated. OBJECTIVES: In the first multischool study of PBL in Canada, we sought to determine the types of feedback (grades, written comments, group feedback from tutor, individual feedback from tutor, peer feedback, self-assessment, no feedback) that students receive as well as their satisfaction with these different feedback modalities. SUBJECTS AND METHODS: We surveyed a sample of 103 final year medical students at the five Ontario schools (University of Toronto, McMaster University, Queens University, University of Ottawa and University of Western Ontario). Subjects were recruited via E-mail and were asked to fill out a questionnaire. RESULTS: Many students felt that the most helpful type of feedback in PBL was individual feedback from the tutor, and indeed, individual feedback was one of the more common types of feedback provided. However, although students also indicated a strong preference for peer and group feedback, these forms of feedback were not widely reported. There were significant differences between schools in the use of grades, written comments, self-assessment and peer feedback, as well as the immediacy of the feedback given. CONCLUSIONS: Across Ontario, students do receive frequent feedback in PBL. However, significant differences exist in the types of feedback students receive, as well as the timing. Although rated highly by students at all schools, the use of peer feedback and self-assessment is limited at most, but not all, medical schools.
Curriculum↗
The effect of frequency of kinetic feedback on learning an isometric force production task in nondisabled subjects.
BACKGROUND AND PURPOSE: The purpose of this study was to investigate the effects of kinetic feedback frequency and concurrent kinetic feedback on the performance and learning of an isometric force production task in young, nondisabled adults. SUBJECTS: Twenty-four nondisabled, right-hand-dominant adults (18 male, 6 female), aged 19 to 33 years (mean = 22.5, SD = 4.1), participated in this study. METHODS: Eight subjects in each of three kinetic feedback groups performed an isometric elbow extension task in an attempt to minimize error between their effort and a force template over a 5-second period. Feedback was provided (1) concurrently with and after each attempt (concurrent feedback), (2) after each attempt (100% feedback), or (3) after every other attempt (50% feedback). Immediate and delayed (48-hour) retention tests were performed without feedback. Separate analyses of variance for repeated measures were used to compare task error among the three feedback groups for acquisition, immediate retention, and delayed retention trials. RESULTS: A significant interaction was found during the acquisition trial blocks, but at each trial block, subjects in the concurrent feedback group exhibited less error than did the subjects in either the 50% or 100% feedback group during the acquisition trials. For the immediate retention test, the 50% and 100% feedback groups exhibited 58% and 39% less error, respectively, than did the concurrent group. For the delayed retention test, the 50% and 100% feedback groups exhibited 52% and 26% less error, respectively, than did the concurrent group. In the immediate and delayed retention tests, subjects in the 50% feedback group displayed less error (31% and 36%, respectively) than did the 100% feedback group. CONCLUSION AND DISCUSSION: When permanent changes in the performance of a motor task are desired, concurrent feedback about task performance may be less desirable than feedback that is provided after the task has been completed. In addition, when feedback was used after the task had been completed, a lower frequency of feedback resulted in more permanent changes in the subjects' ability to complete the task.
Adult↗
Enhancing the learning of sport skills through external-focus feedback.
The authors examined how the effectiveness of feedback for the learning of complex motor skills is affected by the focus of attention it induces. The feedback referred specifically either to body movements (internal focus) or to movement effects (external focus). In Experiment 1, groups of novices and advanced volleyball players (N = 48) practiced "tennis" serves under internal-focus or external-focus feedback conditions in a 2 (expertise) x 2 (feedback type) design. Type of feedback did not differentially affect movement quality, but external-focus feedback resulted in greater accuracy of the serves than internal-focus feedback during both practice and retention, independent of the level of expertise. In Experiment 2, the effects of relative feedback frequency as a function of attentional focus were examined. A 2 (feedback frequency: 100% vs. 33%) x 2 (feedback type) design was used. Experienced soccer players (N = 52) were required to shoot lofted passes at a target. External-focus feedback resulted in greater accuracy than internal-focus feedback did. In addition, reduced feedback frequency was beneficial under internal-focus feedback conditions, whereas 100% and 33% feedback were equally effective under external-focus conditions. The results demonstrate the effectiveness of effect-related, as opposed to movement-related, feedback and also suggest that there is a need to revise current views regarding the role of feedback for motor learning.
Adolescent↗
Effectiveness and cost of different strategies for information feedback in general practice.
AIM: The aim of this study was to determine the effectiveness and relative cost of three forms of information feedback to general practices--graphical, graphical plus a visit by a medical facilitator and tabular. METHOD: Routinely collected, centrally-held data were used where possible, analysed at practice level. Some non-routine practice data in the form of risk factor recording in medical notes, for example weight, smoking status, alcohol consumption and blood pressure, were also provided to those who requested it. The 52 participating practices were stratified and randomly allocated to one of the three feedback groups. The cost of providing each type of feedback was determined. The immediate response of practitioners to the form of feedback (acceptability), ease of understanding (intelligibility), and usefulness of regular feedback was recorded. Changes introduced as a result of feedback were assessed by questionnaire shortly after feedback, and 12 months later. Changes at the practice level in selected indicators were also assessed 12 and 24 months after initial feedback. RESULTS: The resulting cost per effect was calculated to be 46.10 pounds for both graphical and tabular feedback, 132.50 pounds for graphical feedback plus facilitator visit and 773.00 pounds for the manual audit of risk factors recorded in the practice notes. The three forms of feedback did not differ in intelligibility or usefulness, but feedback plus a medical facilitator visit was significantly less acceptable. There was a high level of self-reported organizational change following feedback, with 69% of practices reporting changes as a direct result; this was not significantly different for the three types of feedback. There were no significant changes in the selected indicators at 12 or 24 months following feedback. The practice characteristic most closely related to better indicators of preventive practice was practice size, smaller practices performing significantly better. Separate clinics were not associated with better preventive practice. CONCLUSION: It is concluded that feedback strategies using graphical and tabular comparative data are equally cost-effective in general practice with about two thirds of practices reporting organizational change as a consequence; feedback involving unsolicited medical facilitator visits is less cost-effective. The cost-effectiveness of manual risk factor audit is also called into question.
Cost-Benefit Analysis↗
Increased intracellular Ca++ in the macula densa regulates tubuloglomerular feedback.
BACKGROUND: Tubuloglomerular feedback is initiated by an increase in NaCl at the macula densa lumen, which in turn increases intracellular Ca++. In the present study, we examined the role of increased intracellular Ca++ in tubuloglomerular feedback and the source of the increased Ca++. We hypothesized that an increase in intracellular Ca++ at the macula densa via the basolateral Na+/Ca++ exchanger, caused by an increase in luminal NaCl, initiates Ca++-mediated Ca++ release from intracellular stores, which is essential for tubuloglomerular feedback. METHODS: Rabbit afferent arterioles and attached macula densas were simultaneously microperfused in vitro. Tubuloglomerular feedback was induced by increasing macula densa Na+/Cl- from 11/10 mmol/L (low) to 81/80 mmol/L (high) and was measured before and after treatment. RESULTS: To investigate whether elevations in intracellular Ca++ are required for tubuloglomerular feedback, the calcium ionophore A23187 or the Ca++ chelator BAPTA-AM was added to the macula densa lumen. During the control period, tubuloglomerular feedback decreased afferent arteriole diameter from 18.1 +/- 1.1 microm to 15.3 +/- 0.8 microm. Adding 2 x 10-6 mol/L A23187 to the low NaCl macula densa perfusate induced tubuloglomerular feedback; diameter decreased from 18.0 +/- 1.0 microm to 15.4 +/- 0.9 microm (N = 6; P < 0.01). After adding BAPTA-AM (25 micromol/L) to the macula densa lumen, tubuloglomerular feedback response was completely eliminated. We next studied the source of increased macula densa Ca++ in response to increased NaCl concentration. During the control period, tubuloglomerular feedback decreased afferent arteriole diameter from 18.5 +/- 1.6 microm to 15.3 +/- 1.2 microm (N = 6; P < 0.01). After adding the Na+/Ca++ exchanger inhibitor 2'4'-dichlorobenzamil (10 micromol/L) or KB-R7943 (30 micromol/L) to the bath, the tubuloglomerular feedback response was blocked; however, the afferent arteriole response to angiotensin II or adenosine was not altered. Next, we tested the Ca++-adenosine triphosphatase (ATPase) inhibitor thapsigargin (0.1 micromol/L), which has been reported to inhibit sarcoplasmic reticulum Ca++-ATPase activity and prevent restoration of intracellular Ca++ stores. When thapsigargin was added to the macula densa lumen, it reduced the first tubuloglomerular feedback response by 33% and completely eliminated the second and third tubuloglomerular feedback responses. In the absence of thapsigargin, there was no significant decrease in the tubuloglomerular feedback responses (N = 6). Neither the L-type Ca++ channel blocker nifedipine (25 micromol/L), nor the T-type Ca++ channel blocker pimozide (10 micromol/L), inhibited tubuloglomerular feedback when added to the macula densa lumen. CONCLUSION: We concluded that (1). increased intracellular Ca++ at the macula densa is required for the tubuloglomerular feedback response; (2). Na+/Ca++ exchange appears to initiate Ca++-mediated Ca++ release from intracellular stores; and (3). luminal L-type or T-type Ca++ channels are not involved in tubuloglomerular feedback.
Animals↗
Extrinsic feedback for motor learning after stroke: what is the evidence?
PURPOSE: There is little guidance on using extrinsic feedback to enhance motor learning after stroke. This narrative review synthesises research findings and identifies questions remaining to be answered. METHOD: A summary is given relating to the use of extrinsic feedback in healthy subjects. Then, research concerning content of feedback, feedback scheduling, and attentional focus is discussed in relation to patients with stroke. RESULTS: Though research is scarce, preliminary key findings were as follows: Patients' balance performance can improve from receiving visual feedback about weight distribution during practice; auditory feedback of force production may improve performance of sit-to-stand; providing feedback on less than 100% of trials, and giving summary or average feedback may enhance learning; instructions or feedback inducing an external focus may be more effective than those with an internal focus. Further research is needed concerning the relative benefits of verbal, visual, video and kinematic feedback; reduced feedback frequencies and summary feedback schedules; feedback delays, error estimation, and self-controlled feedback; and attentional focus of feedback. CONCLUSIONS: Although there are some indications that feedback might enhance motor learning after stroke, there are many areas as yet not examined and there is clearly a need for considerable research in this area.
Evidence-Based Medicine↗
Accelerometry-based feedback--can it improve movement consistency and performance in rowing?
The training and competition regimen of elite athletes demands rapid feedback about their performance. The aim of this study was to determine if real-time visual ipsative (comparison with oneself) feedback of instantaneous kinematic consistency improves overall kinematic consistency in rowing. Accelerometry-based data, representing the upper and lower body kinematics, were determined for 13 experienced rowers. Kinematic consistency data -- represented by percentage time outside the acceptable performance bandwidth, performance consistency -- represented by power-stroke dispersion, and several performance indicators were acquired for all the rowers for three 2000 m time trials on a RowPerfect ergometer with three different visual feedback interventions: no feedback, detailed feedback, and summary feedback. Results indicated significantly increased performance consistency for detailed feedback than for both no feedback (p < 0.01) and summary feedback (p < 0.05). No significant difference between summary feedback and no feedback was found (p = 0.173). We deemed feedback of detailed information to enhance kinematic consistency significantly more than both no feedback (p < 0.01) and summary feedback (p < 0.01) interventions, although summary feedback was shown to enhance kinematic consistency more than no feedback (p < 0.01). No improvements were found for performance-related parameters.
Acceleration↗
Understanding the influence of emotions and reflection upon multi-source feedback acceptance and use.
INTRODUCTION: Receiving negative performance feedback can elicit negative emotional reactions which can interfere with feedback acceptance and use. This study investigated emotional responses of family physicians' participating in a multi-source feedback (MSF) program, sources of these emotions, and their influence upon feedback acceptance and use. METHODS: The authors interviewed 28 volunteer family physician participants in a pilot study of MSF, purposefully recruited to represent the range of scores. The study was conducted in 2003-2004 at Dalhousie University. RESULTS: Participants' emotional reactions to feedback appeared to be elicited in response to an internal comparison of their feedback with self-perceptions of performance. Those agreeing with their feedback; i.e., perceiving it as generally consistent with or higher than self-perceptions responded positively, while those disagreeing with their feedback; i.e., seeing it as generally inconsistent with or lower than self-perceptions, generally responded with distress. For the latter group, these feelings were often strong and long-lasting. Some eventually accepted their feedback and used it for change following a long period of reflection. Others did not and described an equally long reflective period but one which focused on and questioned MSF procedures rather than addressed feedback use. Participants suggested providing facilitated reflection on feedback to enhance assimilation of troubling emotions and interpretation and use of feedback. CONCLUSIONS: Negative feedback can evoke negative feelings and interfere with its acceptance. To overcome this, helpful interventions may include raising awareness of the influence of emotions, assisting recipients to focus their feedback on performance tasks, and providing facilitated reflection on feedback.
Education, Medical, Continuing↗
Muscle involvement during intermittent contraction patterns with different target force feedback modes.
OBJECTIVE: Assess the effect of different feedback modes during intermittent contractions on primary and assessory muscle activity. BACKGROUND: Intermittent contractions and physiological responses have been studied in laboratory settings. However, the feedback given to the subjects regarding timing and force level is generally not specified. DESIGN: Repeated measure design in which six subjects in randomized order performed two experimental conditions only differing in feedback mode. METHODS: Intermittent static elbow flexion was performed against either a fixed-force transducer (visual feedback) or a weight to be held in position (proprioceptive feedback) both corresponding to 30% maximal voluntary contraction. Contraction and relaxation timing of 6 and 4 s, respectively, was shown on a VDU screen as colour code identical in both conditions. RESULTS: Test contractions performed before and following 30 min of intermittent contractions showed larger fatigue development with proprioceptive feedback than visual feedback. Also rating of perceived exertion increased more during proprioceptive feedback than visual feedback. This may in part be explained by small differences in the mechanics during the two different feedback modes. In line with this, EMG recorded from four shoulder/arm muscles analyzed for amplitude and frequency showed similar activity initially; but later, during the 30 min contraction larger amplitudes were attained during proprioceptive feedback than visual feedback. CONCLUSIONS: Feedback mode significantly effects the muscle involvement and fatigue during intermittent contractions. RelevanceIntermittent contractions are common in many work places and various feedback modes are being given regarding work requirements. The choice of feedback may significantly affect the muscle load and consequently the development muscle fatigue and disorders.
Biomechanical Phenomena↗
Positive force feedback control of muscles.
This study was prompted by recent evidence for the existence of positive force feedback in feline locomotor control. Our aim was to establish some basic properties of positive force feedback in relation to load compensation, stability, intrinsic muscle properties, and interaction with displacement feedback. In human subjects, muscles acting about the wrist and ankle were activated by feedback-controlled electrical stimulation. The feedback signals were obtained from sensors monitoring force and displacement. The signals were filtered to mimic transduction by mammalian tendon organ and muscle spindle receptors. We found that when muscles under positive force feedback were loaded inertially, they responded in a stable manner with increased active force. The activation attenuated the muscle stretch (yield) that would otherwise occur in the absence of feedback. With enough positive force feedback gain, yield could actually reverse. This behavior, which we termed the affirming reaction, was reminiscent of the mammalian positive supporting reaction, a postural response elicited by contact of the foot with the ground. Muscles under positive force feedback remained stable, even when the loop gain (Gf) was set at levels of 2 or 3. In a linear system, if Gf > 1, instability occurs when the loop is closed. On further investigation, we found that Gf changed with joint angle: it declined as the load-bearing muscle actively shortened. We inferred that in closed-loop operation, the active muscles always shortened until Gf approached unity. In other words, the length-tension curve of active muscle ensures stability even when force-related excitation of motoneurons is very large. Concomitant negative displacement feedback reinforced and stabilized load compensation up to a certain gain, beyond which instability occurred. In further trials we included delays of up to 40 ms in the positive force feedback pathway, to model the delays recently described for tendon organ reflexes in cat locomotion. Contrary to expectations, this did not destabilize the loop. Indeed, when instability was deliberately evoked by setting displacement feedback gain high, delays in the positive force feedback pathway actually stabilized control. The stabilization of positive force feedback by inherent properties of the neuromuscular system increases the functional scope to be expected of feedback from force receptors in biological motor control. Our results provide a rationale for the delayed excitatory action of Ib heteronymous input on extensor motoneurons in cat locomotion.
Adult↗
Audit and feedback: effects on professional practice and health care outcomes.
BACKGROUND: Audit and feedback continues to be widely used as a strategy to improve professional practice. It appears logical that healthcare professionals would be prompted to modify their practice if given feedback that their clinical practice was inconsistent with that of their peers or accepted guidelines. Yet, audit and feedback has not consistently been found to be effective. OBJECTIVES: To assess the effects of audit and feedback on the practice of healthcare professionals and patient outcomes. SEARCH STRATEGY: We searched the Cochrane Effective Practice and Organisation of Care Group's register and pending file up to January 2004. SELECTION CRITERIA: Randomised trials of audit and feedback (defined as any summary of clinical performance over a specified period of time) that reported objectively measured professional practice in a healthcare setting or healthcare outcomes. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and assessed study quality. Quantitative (meta-regression), visual and qualitative analyses were undertaken. For each comparison we calculated the risk difference (RD) and risk ratio (RR), adjusted for baseline compliance when possible, for dichotomous outcomes and the percentage and the percent change relative to the control group average after the intervention, adjusted for baseline performance when possible, for continuous outcomes. We investigated the following factors as possible explanations for the variation in the effectiveness of interventions across comparisons: the type of intervention (audit and feedback alone, audit and feedback with educational meetings, or multifaceted interventions that included audit and feedback), the intensity of the audit and feedback, the complexity of the targeted behaviour, the seriousness of the outcome, baseline compliance and study quality. MAIN RESULTS: Thirty new studies were added to this update, and a total of 118 studies are included. In the primary analysis 88 comparisons from 72 studies were included that compared any intervention in which audit and feedback is a component compared to no intervention. For dichotomous outcomes the adjusted risk difference of compliance with desired practice varied from - 0.16 (a 16 % absolute decrease in compliance) to 0.70 (a 70% increase in compliance) (median = 0.05, inter-quartile range = 0.03 to 0.11) and the adjusted risk ratio varied from 0.71 to 18.3 (median = 1.08, inter-quartile range = 0.99 to 1.30). For continuous outcomes the adjusted percent change relative to control varied from -0.10 (a 10 % absolute decrease in compliance) to 0.68 (a 68% increase in compliance) (median = 0.16, inter-quartile range = 0.05 to 0.37). Low baseline compliance with recommended practice and higher intensity of audit and feedback were associated with larger adjusted risk ratios (greater effectiveness) across studies. AUTHORS' CONCLUSIONS: Audit and feedback can be effective in improving professional practice. When it is effective, the effects are generally small to moderate. The relative effectiveness of audit and feedback is likely to be greater when baseline adherence to recommended practice is low and when feedback is delivered more intensively.
Education, Medical, Continuing↗
Systematic review of the literature on assessment, feedback and physicians' clinical performance: BEME Guide No. 7.
BACKGROUND AND CONTEXT: There is a basis for the assumption that feedback can be used to enhance physicians' performance. Nevertheless, the findings of empirical studies of the impact of feedback on clinical performance have been equivocal. OBJECTIVES: To summarize evidence related to the impact of assessment and feedback on physicians' clinical performance. SEARCH STRATEGY: The authors searched the literature from 1966 to 2003 using MEDLINE, HealthSTAR, the Science Citation Index and eight other electronic databases. A total of 3702 citations were identified. INCLUSION AND EXCLUSION CRITERIA: Empirical studies were selected involving the baseline measurement of physicians' performance and follow-up measurement after they received summaries of their performance. DATA EXTRACTION: Data were extracted on research design, sample, dependent and independent variables using a written protocol. DATA SYNTHESIS: A group of 220 studies involving primary data collection was identified. However, only 41 met all selection criteria and evaluated the independent effect of feedback on physician performance. Of these, 32 (74%) demonstrated a positive impact. Feedback was more likely to be effective when provided by an authoritative source over an extended period of time. Another subset of 132 studies examined the effect of feedback combined with other interventions such as educational programmes, practice guidelines and reminders. Of these, 106 studies (77%) demonstrated a positive impact. Two additional subsets of 29 feedback studies involving resident physicians in training and 18 studies examining proxy measures of physician performance across clinical sites or groups of patients were reviewed. The majority of these two subsets also reported that feedback had positive effects on performance. HEADLINE RESULTS: Feedback can change physicians' clinical performance when provided systematically over multiple years by an authoritative, credible source. CONCLUSIONS: The effects of formal assessment and feedback on physician performance are influenced by the source and duration of feedback. Other factors, such as physicians' active involvement in the process, the amount of information reported, the timing and amount of feedback, and other concurrent interventions, such as education, guidelines, reminder systems and incentives, also appear to be important. However, the independent contributions of these interventions have not been well documented in controlled studies. It is recommended that the designers of future theoretical as well as practical studies of feedback separate the effects of feedback from other concurrent interventions.
Clinical Competence↗
Role of macula densa adenosine triphosphate (ATP) in tubuloglomerular feedback.
BACKGROUND: Recent studies have shown that adenosine triphosphate (ATP) is liberated from macula densa cells in response to increased tubular NaCl in vitro. We tested the hypothesis that increased NaCl in the macula densa stimulates the release of ATP, resulting in extracellular formation of adenosine which is involved in signal transmission of the tubuloglomerular feedback response. METHODS: Rabbit afferent arterioles and attached macula densas were simultaneously microperfused in vitro. Tubuloglomerular feedback was induced by increasing macula densa Na/Cl from 11/10 to 81/80 mmol/L and was measured before and after treatment. RESULTS: We first tested whether hydrolysis of ATP is required for tubuloglomerular feedback. When we enhanced conversion of ATP to adenosine by adding hexokinase or apyrase to the bath and arteriole lumen, the tubuloglomerular feedback response was augmented. During the control period, tubuloglomerular feedback decreased arteriole diameter by 2.2 +/- 0.2 microm. In the presence of hexokinase, tubuloglomerular feedback decreased diameter by 3.4 +/- 0.3 microm (N= 8) (P < 0.05, with vs. without hexokinase). In the apyrase group, tubuloglomerular feedback decreased diameter by 2.7 +/- 0.4 microm during the control period. When apyrase was added, tubuloglomerular feedback decreased diameter by 4.7 +/- 0.4 microm (N= 8) (P < 0.05, with vs. without apyrase). When hydrolysis of adenosine monophosphate (AMP) to adenosine was blocked by supplementing the bath with 100 micromol/L alpha,beta-methylene adenosine 5'-diphosphate (MADP), an inhibitor of 5'-nucleotidase, tubuloglomerular feedback response was blocked and diameter remained unchanged. We next studied whether ATP released from the macula densa binds to P(2) receptors and activates the tubuloglomerular feedback response. The P(2) purinergic receptor inhibitor suramin was added to both arteriole lumen and bath. During the control period, tubuloglomerular feedback decreased diameter by 3.7 +/- 0.5 microm. Suramin (100 micromol/L) did not significantly inhibit tubuloglomerular feedback, since in the presence of suramin diameter decreased by 3.8 +/- 0.3 microm (N= 7). Finally, we added the adenosine A(1) receptor inhibitor FK838 to both bath and lumen and found that it completely blocked high NaCl-induced tubuloglomerular feedback. CONCLUSION: We concluded that ATP released from the macula densa is broken down to form AMP in the extracellular space. AMP in turn is degraded by ecto-5'-nucleotidases to adenosine, which mediates signal transmission of the tubuloglomerular feedback response.
5'-Nucleotidase↗
Implications of positive feedback in the control of movement.
In this paper we review some theoretical aspects of positive feedback in the control of movement. The focus is mainly on new theories regarding the reflexive role of sensory signals from mammalian tendon organ afferents. In static postures these afferents generally mediate negative force feedback. But in locomotion there is evidence of a switch to positive force feedback action. Positive feedback is often associated with instability and oscillation, neither of which occur in normal locomotion. We address this paradox with the use of analytic models of the neuromuscular control system. It is shown that positive force feedback contributes to load compensation and is surprisingly stable because the length-tension properties of mammalian muscle provide automatic gain control. This mechanism can stabilize control even when positive feedback is very strong. The models also show how positive force feedback is stabilized by concomitant negative displacement feedback and, unexpectedly, by delays in the positive feedback pathway. Other examples of positive feedback in animal motor control systems are discussed, including the beta-fusimotor system, which mediates positive feedback of displacement. In general it is seen that positive feedback reduces the sensitivity of the controlled extremities to perturbations of posture and load. We conclude that positive force feedback can provide stable and effective load compensation that complements the action of negative displacement and velocity feedback.
Afferent Pathways↗