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At least 433 records · Page 24Linked to original sources
PubMed2006

Semiconductor laser under resonant feedback from a Fabry-Perot resonator: Stability of continuous-wave operation.

We study the continuous-wave (cw) operation of a semiconductor laser subject to optical feedback from a Fabry-Perot resonator in a case where the emission is resonant to a reflection minimum of the resonator. This configuration is treated in the framework of Lang-Kobayashi equations. The nature of bifurcations and the stability of steady state solutions is analyzed in terms of the dependence on magnitude and phase of the feedback. In contrast to conventional optical feedback from a single mirror, the locus of external cavity modes is not elliptic but represents a tilted eight with possible satellite bubbles. Below a critical feedback strength, which is analytically given, only one single mode exists representing the completely unchanged cw emission of the laser. In this weak-feedback regime, the feedback phase allows noninvasive control of the cw emission and a tailoring of its small-signal response within wide limits. The results obtained are a prototype for all-optical realizations of delayed feedback control.

Journal Article↗
PubMed2003

Short term effect of feedback on fitness and health measurements on self reported appraisal of the stage of change.

BACKGROUND: An individual's current status of physical activity and nutrition and readiness to change can be determined using PACE assessment forms. Practitioners have suggested that feedback on the fitness and health components can produce a change in a subject's awareness of their behaviour and thereby lead to a beneficial change in stage of behaviour change. OBJECTIVE: To evaluate the short term effect of personalised feedback on fitness and health status on self reported appraisal of the stage of change. METHODS: A total of 299 civil servants were randomised to an intervention or a reference group. After having been tested for fitness and health, the intervention group received immediate feedback on their test results, whereas the reference group did not. PACE assessment forms were completed twice: before testing and after testing (reference group), or after testing and feedback (intervention group). The time interval between was one hour. The influence of feedback was determined using a x(2) test and analysis of variance. RESULTS: On the basis of the x(2) test, no significant effect of feedback was found on the stage of change of physical activity, nor on the stage of change with regard to nutrition. Analysis of variance results showed no significant effect on the raw PACE score as to physical activity, intake of fruit and vegetables and dietary fat. However, a significant effect was observed on the PACE score of "calorie intake and weight management". Subjects in the intervention group significantly more often regressed on their PACE score on this topic than the reference subjects. CONCLUSIONS: Feedback at baseline on measurements of an intervention study can influence PACE scores and can be considered as a small but relevant start of the intervention itself.

Adaptation, Psychological↗
PubMed2004

Contribution of force feedback to ankle extensor activity in decerebrate walking cats.

Previous investigations have demonstrated that feedback from ankle extensor group Ib afferents, arising from force-sensitive Golgi tendon organs, contributes to ankle extensor activity during the stance phase of walking in the cat. The objective of this investigation was to gain insight into the magnitude of this contribution by determining the loop gain of the positive force feedback pathway. Loop gain is the relative contribution of force feedback to total muscle activity and force. In decerebrate cats, the isolated medial gastrocnemius muscle (MG) was held at different lengths during sequences of rhythmic contractions associated with walking in the other three legs. We found that MG muscle activity and force increased at longer muscle lengths. A number of observations indicated that this length dependence was not due to feedback from muscle spindles. In particular, activity in group Ia afferents was insensitive to changes in muscle length during the MG bursts, and electrical stimulation of group II afferents had no influence on the magnitude of burst activity in other ankle extensors. We concluded that the homonymous positive force feedback pathway was isolated from other afferent pathways, allowing the use of a simple model of the neuromuscular system to estimate the pathway loop gain. This gain ranged from 0.2 at short muscle lengths to 0.5 at longer muscle lengths, demonstrating that force feedback was of modest importance at short muscle lengths, accounting for 20% of total activity and force, and of substantial importance at long muscle lengths, accounting for 50%. This length dependence was due to the intrinsic force-length property of muscle. The gain of the pathway that converts muscle force to motoneuron depolarization was independent of length. We discuss the relevance of this conclusion to the generation of ankle extensor activity in intact walking cats. These findings emphasize the general importance of feedback in generating ankle extensor activity during walking in the cat.

Algorithms↗
PubMed2006

The effect of visual feedback plus mental practice on symmetrical weight-bearing training in people with hemiparesis.

OBJECTIVE: To investigate the effect of visual feedback with mental practice on symmetrical weight-bearing training in three individuals with hemiparetic stroke. DESIGN: A single-subject experimental design, alternating with multiple baselines across individuals. SETTING: Laboratory of a department of occupational therapy. PARTICIPANTS: Three individuals with left hemiparesis from stroke. INTERVENTION: Visual feedback with mental practice on symmetrical weight-bearing training. MAIN OUTCOME MEASURES: The proportion of the participant's weight-bearing by the affected limb while standing was measured using Limloader. RESULTS: For participants 1, 2 and 3, the respective average weight-bearing proportions of the affected limb were 27%, 31% and 21% at baseline, 47%, 48% and 47% after visual feedback with mental practice, and 42%, 48% and 42% after visual feedback only, immediately following each training session. When the participants had visual feedback with mental practice, they placed a greater proportion of their weight on the affected limb, and this effect was maintained for 1 h. CONCLUSION: These findings indicate that the visual feedback approach alone can effect improvement but visual feedback together with mental practice produces further positive effect on improving and maintaining a symmetrical stance posture in people with hemiparetic stroke.

Aged↗
PubMed1994

INTEGRATION OF POSITIVE AND NEGATIVE FEEDBACK LOOPS IN A CRAYFISH MUSCLE

It is now well established that in arthropods movement-related feedback may produce positive, as well as negative, feedback reflexes (Bassler, 1976; DiCaprio and Clarac, 1981; Skorupski and Sillar, 1986; Skorupski et al. 1992; Vedel, 1980; Zill, 1985). Usually the same motor neurones are involved in both negative feedback (resistance) reflex responses and positive feedback reflexes. Reflex reversal involves a shift in the pattern of central inputs to a motor neurone, for example from excitation to inhibition. In the crayfish, central modulation of reflexes has been described in some detail for two basal limb proprioceptors, the thoracocoxal muscle receptor organ (TCMRO) and the thoracocoxal chordotonal organ (TCCO) (Skorupski et al. 1992; Skorupski and Bush, 1992). Leg promotor motor neurones are excited by stretch of the TCMRO (which, in vivo, occurs on leg remotion) in a negative feedback reflex, but when this reflex reverses they are inhibited by the same stimulus. Release of the TCCO (which corresponds to leg promotion) excites some, but not all, promotor motor neurones in a positive feedback reflex. There are at least two ways in which the reflex control of a muscle may be modulated in this system. Firstly, inputs to motor neurones may be routed via alternative reflex pathways to produce different reflex outputs. Secondly, the pattern of inputs to a motor pool may be inhomogeneous, so that activation of different subgroups of the motor pool causes different outputs. Different crayfish promotor motor neurones are involved in different reflexes. On this basis, the motor neurones may be classified into at least two subgroups: those that are excited by the TCCO in a positive feedback reflex (group 1) and those that are not (group 2). Do these motor neurone subgroups have different effects on the promotor muscle, or is the output of the two promotor subgroups summed at the neuromuscular level? To address this question we recorded from the promotor nerve and muscle in a semi-intact preparation of the crayfish, Pacifastacus leniusculus. Adult male and female crayfish, 8-11 cm rostrum to tail, were decapitated and the tail, carapace and viscera removed. The sternal artery was cannulated and perfused with oxygenated crayfish saline, as described previously (Sillar and Skorupski, 1986).

Journal Article↗
PubMed2006

Analysis of the effects of feedback asymmetry in external cavity He-Ne lasers.

A theoretical analysis of the characteristics of an external cavity He-Ne laser with asymmetric feedback induced by the misalignment of an external feedback mirror is proposed. The theoretical model considers both the multiple reflections and the phase variation caused by the asymmetric external cavity. It is found that the phase variation is of importance in determining the effects of asymmetric feedback. The three-order asymmetric feedback effects are experimentally observed and can be interpreted well by this model. The fringe frequency of the asymmetric optical feedback system can also be increased. The experimental results are in good agreement with the theoretical analysis. The theoretical and experimental results offer a potential increase in the resolution of an optical feedback system with asymmetric feedback.

Journal Article↗
PubMed2006

High-frequency intensity modulation in orthogonal polarized dual frequency lasers with optical feedback.

High-frequency modulation of laser output intensity is studied with asymmetric feedback induced by the misalignment of an external feedback reflector in an orthogonal polarized dual frequency laser. The fringe frequency of the optical feedback system is seven times higher than that of a conventional optical feedback system, due to multiple feedback effects. The output characteristics of two orthogonal polarized modes are also investigated. Mode competition is observed between the two modes. When initial intensities of the two modes are unequal, the mode competition will be strong. The difference in initial intensity between the two orthogonally polarized modes plays an important role in the mode competition with optical feedback. Experimental results are presented, as well as a theoretical explanation. The high-frequency modulation of laser intensity can greatly increase the resolution of an optical feedback sensing system.

Journal Article↗
PubMedDate not supplied

Improving test ordering in primary care: the added value of a small-group quality improvement strategy compared with classic feedback only.

PURPOSE: We wanted to evaluate the added value of small peer-group quality improvement meetings compared with simple feedback as a strategy to improve test-ordering behavior. Numbers of tests ordered by primary care physicians are increasing, and many of these tests seem to be unnecessary according to established, evidence-based guidelines. METHODS: We enrolled 194 primary care physicians from 27 local primary care practice groups in 5 health care regions (5 diagnostic centers). The study was a cluster randomized trial with randomization at the local physician group level. We evaluated an innovative, multifaceted strategy, combining written comparative feedback, group education on national guidelines, and social influence by peers in quality improvement sessions in small groups. The strategy was aimed at 3 specific clinical topics: cardiovascular issues, upper abdominal complaints, and lower abdominal complaints. The mean number of tests per physician per 6 months at baseline and the physicians' region were used as independent variables, and the mean number of tests per physician per 6 months was the dependent variable. RESULTS: The new strategy was executed in 13 primary care groups, whereas 14 groups received feedback only. For all 3 clinical topics, the decrease in mean total number of tests ordered by physicians in the intervention arm was far more substantial (on average 51 fewer tests per physician per half-year) than the decrease in mean number of tests ordered by physicians in the feedback arm (P = .005). Five tests considered to be inappropriate for the clinical problem of upper abdominal complaints decreased in the intervention arm, with physicians in the feedback arm ordering 13 more tests per 6 months (P = .002). Interdoctor variation in test ordering decreased more in the intervention arm. CONCLUSION: Compared with only disseminating comparative feedback reports to primary care physicians, the new strategy of involving peer interaction and social influence improved the physicians' test-ordering behavior. To be effective, feedback needs to be integrated in an interactive, educational environment.

Abdominal Pain↗
PubMed1976

Decreasing fuel-oil consumption through feedback and social commendation.

The energy crisis of the winter of 1973-74 led to severe shortages of fuel oil for home heating and a government request for voluntary conservation by the oil consumer. This experiment tested two methods of facilitating fuel-oil conservation. Home fuel-oil consumers were randomly assigned to one of three experimental groups: feedback of information on rate of oil use, feedback plus commendation for reduced consumption, or a no-treatment control. The consumption rate for the feedback plus commendation group was significantly lower than that of either the informational feedback group or the control group. The informational feedback group did not differ from the control group. The results suggest that feedback alone may not result in oil conservation, but that feedback combined with commendation can produce socially significant savings.

Journal Article↗
PubMed1977

The role of feedback in voluntary control of blood pressure in instructed subjects.

Forty normal male volunteers were randomly assigned to one of four experimental conditions and instructed to raise and lower their systolic blood pressure. Subjects received either beat-to-beat feedback contingent on pressure changes, noncontingent beat-to-beat feedback, noncontingent feedback presented randomly with respect to the occurrence of each heart beat, or instructions alone. The order of increase and decrease trial blocks was counterbalanced across groups. Subjects receiving contingent feedback were monetarily rewarded for appropriate pressure changes. Subjects receiving noncontingent feedback received rewards and feedback equal to the mean received by the contingent group. Subjects in the instructions-only condition were also paid this bonus but were informed of their earnings only at the conclusion of the experiment. Results indicated that in the presence of instructions, feedback, whether contingent or noncontingent, added little to subjects' ability to control pressure during a single session. Theoretical and clinical implications are discussed.

Adolescent↗
PubMed1981

Reduction of residential consumption of electricity through simple monthly feedback.

Feedback has been widely used in efforts to control the consumption of electricity. Previous efforts, however, have used forms of feedback that seem economically impractical. The present study examined the effects of a feasible program of monthly feedback. Forty matched nonvolunteer participants were randomly divided into two groups: a no-contact control group and a monthly feedback group. In an A-B-A design, the data showed a clear decrease in electricity consumption for the feedback group during the feedback phase. The effect was maintained during a 4-mo intervention period. Withdrawal of the feedback was associated with a return to higher levels of electricity consumption.

Journal Article↗
PubMed1969

A response-spacing effect: an absence of responding during response-feedback stimuli.

In most studies of operant reinforcement a response-feedback stimulus is used which is so brief that the nature of the responding during it is virtually undetectable. The present study investigated the nature of this responding by lengthening an initially brief feedback stimulus. The key-pecking responses of pigeons were maintained by a variable-interval schedule of food reinforcement. Each response produced a brief stimulus light in addition to the usual auditory response feedback. When the duration of the feedback stimulus light was gradually increased, it was found to control a nearly zero rate of responding. The result was a paced, metronomic-like performance in which the pigeon made a single response, paused until the stimulus terminated, and then responded again. As a result, the overall response rate was greatly reduced; the mean interresponse time approximated the stimulus duration. A plausible interpretation is that brief feedback stimuli acquire control over responding because they coincide with few responses and few reinforcers. These findings show that in addition to their known functions as conditioned-reinforcing stimuli and discriminative stimuli, response-feedback stimuli also exert direct stimulus control: responding is reduced during the feedback stimulus itself.

Journal Article↗
PubMed1996

Efficacy of feedback from quarterly laboratory comparison in maintaining quality of a hospital capillary blood glucose monitoring program.

OBJECTIVE: A 1-year randomized prospective study was conducted to investigate the efficacy of feedback from split-sample testing as part of a capillary blood glucose quality assurance program. RESEARCH DESIGN AND METHODS: A total of 124 nurses were randomized to either group A (quarterly comparisons with feedback) or group B (no feedback). The measure of nurse accuracy against the laboratory at 0, 6, and 12 months was determined by an additional five to seven split-sample tests without giving feedback to either group. Mean accuracy was determined in terms of percent absolute deviation from the laboratory result and a clinical consensus limit of +/- 20% deviation from the laboratory. RESULTS: By 12 months, there was a significant effect of feedback on nurse agreement with the laboratory method (P = 0.022 when agreement was scored as the mean percent absolute difference and P = 0.002 when agreement was scored in terms of the +/- 20% clinical consensus limit). Nurses in the group who had received no quarterly feedback from split-sample testing produced a 3.5% greater mean percent absolute deviation from the laboratory method and 12% fewer comparisons within the acceptable +/- 20% range. CONCLUSIONS: Feedback received from split-sample testing has a significant effect in maintaining accuracy in capillary blood glucose monitoring.

Blood Glucose↗
PubMed2005

The use of real-time ultrasound feedback in teaching abdominal hollowing exercises to healthy subjects.

STUDY DESIGN: Randomized controlled trial. OBJECTIVES: To determine if supplementing typical clinical instruction with real-time ultrasound feedback facilitates performance and retention of the abdominal hollowing exercise (AHE). BACKGROUND: Increasingly clinicians are using real-time ultrasound imaging as a form of feedback when teaching patients trunk stabilization exercises; however, there has been no justification for this practice. METHODS AND MEASURES: Forty-eight subjects were divided randomly into 3 groups that received different types of feedback: group 1 received minimal verbal feedback, group 2 received verbal and palpatory feedback, and group 3 received real-time ultrasound, verbal, and palpatory feedback. If the subject performed 3 consecutive correct AHEs during the initial session, she/he returned for a retention test. The performance of 3 consecutive, correct AHEs was the criterion measure; the number of trials to criterion was also recorded during the initial and retention test sessions. RESULTS: The ability to perform the AHE differed among groups (P<.001). During the initial session, 12.5% of subjects in group 1, 50.0% of subjects in group 2, and 87.5% of subjects in group 3 were able to perform 3 consecutive AHEs. Group 3 subjects achieved the criterion in fewer trials than the other 2 groups (P = .0006). No differences among groups were found for the retention testing; however, low power due to fewer subjects precluded a strong interpretation of this finding. CONCLUSION: Real-time ultrasound feedback can decrease the number of trials needed to consistently perform the AHE; however, the data are inconclusive with regard to retention of this skill.

Abdominal Muscles↗
PubMed1982

Effect of EMG feedback on paretic muscles and abnormal co-contraction in the hemiplegic arm, compared with conventional physical therapy.

The effectiveness of EMG feedback in hemiparetic patients with an impaired arm and hand function was compared with conventional physical therapy in 18 patients, who were assigned to two groups. EMG feedback in the experimental group (n = 9) was confined to augmenting the reduced muscle activity in one proximal and one distal agonist, and to decreasing the excessive activity in one proximal antagonist and in two distal muscle groups. The control group (n = 9) was treated with conventional physical therapy. Overall duration for both treatments was 2 1/2 moths, which included 28 sessions of one hour, three times a week. Major differences in the effect of EMG feedback were found in abnormal co-contractions as compared with reduced muscle activity in agonists. The most prominent effect was found at the end of the EMG feedback training in abnormal co-contractions. Several days after ending the EMG feedback a decrease in abnormal co-contractions in the exclusively trained muscles could still be demonstrated, compared with abnormal co-contractions in untrained muscles and abnormal co-contractions in muscles treated with conventional physical therapy. However, part of the effect was lost. By contrast, intensive EMG feedback therapy had no specific effect on proximal and distal agonists of the hemiplegic arm, when compared with conventional physical therapy of a long duration. The performance of isolated voluntary movements, the occurrence of pathological associated movements and the function of the arm and the hand were not affected by the EMG feedback therapy, or by conventional physical therapy.

Adult↗
PubMed2000

Endogenous DA-mediated feedback inhibition of DA neurons: involvement of both D(1)- and D(2)-like receptors.

To investigate the role of D(1)-like receptors in endogenous dopamine (DA)-mediated feedback control of DA neurons in vivo, single unit recordings were made from rat nigral DA cells using low cerveau isolé preparations. The D(2) antagonist raclopride, but not the D(1) antagonist SCH23390, increased baseline activity of DA neurons, suggesting that spontaneously released DA acts primarily through D(2)-like receptors to inhibit DA cells. However, feedback inhibition induced by an increased DA release by D-amphetamine (1 mg/kg, i.v.) was partially reversed by SCH23390. The same inhibition, on the other hand, was always completely reversed by raclopride, suggesting that the D(1)-mediated portion of the inhibition depends upon co-activation of D(2)-like receptors. In rats with forebrain hemitransections, D-amphetamine-induced inhibition was markedly decreased and the remaining inhibition was not blocked by SCH23390, supporting the suggestion that D(1)-D(2) co-activation-induced inhibition is mediated through long feedback pathways. In chloral hydrate-anesthetized rats, D-amphetamine-induced inhibition was also insensitive to SCH23390; however, the degree of the inhibition was not reduced. Combined with previous studies, these data suggest that chloral hydrate not only inactivates the D(1) feedback pathway but also enables the D(2) feedback pathway to operate independently of D(1)-like receptors. Conversely, in parkinsonian animals D(1) receptor activation alone has been reported to inhibit DA cells. Taken together, these results suggest that a major portion of endogenous DA-mediated feedback inhibition is due to concurrent activation of D(1)- and D(2)-like receptors. However, this D(1)-D(2) interdependence may alter under certain conditions and may play a role in the pathophysiology of Parkinson's disease.

Animals↗
PubMed1979

Influence of modelling and feedback provided by the supervisors in a microskills training program for beginning counsellors.

Investigated the influence of modelling and feedback on the effectiveness of a microskills training program for beginning counsellors. The microskills taught were: attending behavior, minimal encourages to talk, open questions, and reflection of feeling and content. Twenty-four trainee counsellors were allocated to three treatment groups: (1) no modelling, no feedback (NMF); (2) modelling and feedback from the supervisor (MF); and (3) feedback from the supervisor (F). Analysis of variance showed that MF was superior to NMF and F in increasing use of the skill reflection of feeling. These results lead to the conclusion that the microskills taught differ in level of difficulty, and, hence, in the amount of information, through instructions, practice, modelling or feedback, that will bring these skills to ceiling level. Supervisor modelling and feedback appear to improve learning of the comparatively difficult skill, reflection of feeling.

Affect↗
PubMed2007

Coupled positive and negative feedback circuits form an essential building block of cellular signaling pathways.

Cellular circuits have positive and negative feedback loops that allow them to respond properly to noisy external stimuli. It is intriguing that such feedback loops exist in many cases in a particular form of coupled positive and negative feedback loops with different time delays. As a result of our mathematical simulations and investigations into various experimental evidences, we found that such coupled feedback circuits can rapidly turn on a reaction to a proper stimulus, robustly maintain its status, and immediately turn off the reaction when the stimulus disappears. In other words, coupled feedback loops enable cellular systems to produce perfect responses to noisy stimuli with respect to signal duration and amplitude. This suggests that coupled positive and negative feedback loops form essential signal transduction motifs in cellular signaling systems.

Animals↗