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PubMed2003

Stability of bipedal stance: the contribution of cocontraction and spindle feedback.

The aim of this study is to assess the contribution of cocontraction and spindle feedback to local stability during bipedal stance. To that aim, an existing nonlinear state space model of the human musculoskeletal system is linearized in a reference equilibrium state. The maximal real part of the eigenvalues of the linearized system matrix A and the low-frequency joint stiffness are used as a measure of local stability. Muscle properties, as represented in a Hill-type muscle model, are shown to improve the behavior, the improvement being larger at high cocontraction. However, even at maximal cocontraction the low-frequency joint stiffness generated by the muscle properties is insufficient to yield a locally stable system. It follows that feedback is necessary to ensure local stability. In this study, the potential contribution of spindle feedback is investigated by optimizing the feedback gains for contractile element length and velocity for each muscle. It is found that in the case of time-delayed negative feedback, it is impossible to stabilize the system on the basis of spindle feedback. When positive time-delayed feedback is allowed, a barely stable system is obtained. When the time delays are removed, the feedback gains can be chosen such that a locally stable system is obtained, indicating the limitations imposed by the presence of time delays. Finally, it is shown that for small perturbations the response of the linear system to an arbitrary perturbation is similar to that of the nonlinear system, indicating the validity of the approach used. It is concluded that the combination of muscle properties and time-delayed spindle feedback is insufficient to obtain a system with reasonable local stability.

Feedback↗
PubMed2001

Error monitoring in the hemispheres: the effect of lateralized feedback on lexical decision.

Does each hemisphere have its own system for monitoring and responding to errors? Three experiments investigate the effect of presenting lateralized accuracy feedback in a bilateral lexical decision task. We presented feedback after each trial in either the left visual field (LVF) or right visual field (RVF). In Experiment 1 the feedback stimuli were faces smiling or frowning, in Experiment 2 we used colored squares, and Experiment 3 tested the effect of verbal feedback. Negative feedback presented in the LVF tended to improve performance on the following trial, while the same negative feedback in the RVF tended to disrupt performance on the following trial. This result was strongest with the faces as feedback, was less pronounced with colored squares, and disappeared with verbal feedback. The results are interpreted as suggesting a right hemisphere superiority for error monitoring that depends on the mode of feedback.

Analysis of Variance↗
PubMed2004

Multiple feedback loops are key to a robust dynamic performance of tryptophan regulation in Escherichia coli.

Living systems must adapt quickly and stably to uncertain environments. A common theme in cellular regulation is the presence of multiple feedback loops in the network. An example of such a feedback structure is regulation of tryptophan concentration in Escherichia coli. Here, three distinct feedback mechanisms, namely genetic regulation, mRNA attenuation and enzyme inhibition, regulate tryptophan synthesis. A pertinent question is whether such multiple feedback loops are "a case of regulatory overkill, or do these different feedback regulators have distinct functions?" Another moot question is how robustness to uncertainties can be achieved structurally through biological interactions. Correlation between the feedback structure and robustness can be systematically studied by tools commonly employed in feedback theory. An analysis of feedback strategies in the tryptophan system in E. coli reveals that the network complexity arising due to the distributed feedback structure is responsible for the rapid and stable response observed even in the presence of system uncertainties.

Computer Simulation↗
PubMed1997

Feedback strategies for visual search in airframe structural inspection.

Feedback of information has consistently shown positive results in human inspection, provided it is given in a timely and appropriate manner. Feedback serves as the basis of most training schemes; traditionally this has been performance feedback. Other forms of feedback which provide strategy information rather than performance information may have a role in improving inspection. This study compared performance feedback and cognitive feedback in a realistic simulation of an aircraft structural inspection task. Performance (time, errors) feedback showed the greatest improvements in performance measures. Cognitive feedback enhanced efficiency measures of search strategy. When cognitive feedback consisted of visual representations of the path and the coverage of the search sequence, subjects also were able to use this task information to improve their search performance.

Adult↗
PubMed1998

A new method for evaluation and dietary therapy of congenital: deficiencies of amino acid metabolic enzymes. Linear system analysis and optimization of feedback inputs for the metabolic pathways of lysine, methionine and isoleucine.

We intended to elucidate an integrated mathematical model of amino acid metabolism and we propose a system for optimization treatment of disturbed metabolic states caused by congenital enzyme deficiencies. Our analysis focused on the metabolic pathway starting at asparaginic acid proceeding to isoleucine, methionine and lysine. The rate of change in the concentration of the biochemical species was expressed as 21 linear rate equations. We obtained the rate constants and the magnitude of feedback from reported experimental data. Linear systems analysis revealed that the metabolic system under study was stable but uncontrollable. These properties were insensitive to changes in the magnitude of feedback. To show the effect of optimizing the feedback so that it minimizes the square of the concentration of the species and the control input, we analyzed the impulse response of the species, transient response and the singular value of the system for four cases; (1) at the physiological state without optimizing the feedback, (2) at the physiological state attained after optimizing the feedback, (3) at the pathophysiological state attained with enzyme deficiency states for lysine and methionine metabolism without optimizing the feedback, and (4) at the pathophysiological state attained after optimizing the feedback for enzyme deficiencies. In the enzyme deficient model, the impulse response oscillated and lasted longer than that in the physiological state. These changes appeared even in the species on other branched pathways. The singular value was elevated in the enzyme deficient state. By optimizing the feedback, all the impulse responses in the enzyme deficient state recovered to nearly those in the normal physiological state. Similarly, the transient response and the singular value in the enzyme deficient state recovered to nearly the normal physiological values. We elucidated the numerical value of the feedback gain for this optimization. The present analysis is useful for the evaluation of the integrated properties of amino acid metabolism and the optimization technique is potentially of use for determining a treatment course for congenital metabolic enzyme deficiencies.

Amino Acid Metabolism, Inborn Errors↗
PubMed1997

Stress-restress: effects on ACTH and fast feedback.

Glucocorticoid secretion is tightly regulated by negative feedback. Glucocorticoid feedback has been found to be altered in depression and post-traumatic stress disorder (PTSD). While hyposensitive glucocorticoid feedback has been found in depression, hypersensitive or enhanced negative feedback was described in PTSD. Enhanced negative feedback, can be seen as a sensitization of the inhibitory elements of HPA axis, and stress-restress or time dependent sensitization (TDS) model, has been suggested as an animal model for PTSD. We have studied the effects of this model on the HPA axis to determine whether it will produce increased sensitivity to negative feedback as found in PTSD patients. Adult Sprague-Dawley male rats were exposed to a single session of prolonged stress (restraint followed by a forced swim and exposure to ether vapors) and briefly restressed 7 days later. The effects of single prolonged stress on plasma ACTH and corticosterone responses (0, 5, and 30 min) and on glucocorticoid fast feedback (cortisol vs. saline pretreatment) were assessed in two studies. Animals exposed to single prolonged stress showed enhanced negative feedback in comparison to naive animals (F = 4.6371, df = 3, p = .0107), but there was no difference in ACTH or corticosterone responses during the restress. Pretreatment with cortisol, in the first stress session, did not prevent the development of the enhanced fast feedback when restressed. This can be seen as a sensitization of the inhibitory elements of HPA axis, suggesting that stress-restress paradigm might serve as a good animal model for HPA abnormalities found in PTSD patients.

Adrenocorticotropic Hormone↗
PubMed2004

Effects of speech and print feedback on spelling by children with autism.

In this systematic replication of a previous study (R. W. Schlosser, D. M. Blischak, P. J. Belfiore, C. Bartley, and N. Barnett, 1998), the effects of speech and print feedback on spelling performance were evaluated. Four children with autism and no functional speech were taught to spell words with a speech-generating device under 3 feedback conditions. In the auditory-visual condition, children received both speech and print feedback, whereas in the auditory and visual conditions, only 1 type of feedback was provided. An adapted alternating treatments design was used. All 4 children reached criterion across conditions. Although 3 children reached criterion first with print or speech-print feedback, 1 child was most efficient with speech-print followed by speech feedback. Based on the findings of both studies, 2 distinct profiles of feedback efficiency are proposed. Children that exemplify the primarily visual profile spell words most efficiently when feedback involves print. Children that fit the auditory profile spell words most efficiently when feedback involves speech. The implications for understanding the learning characteristics of children with autism, as well as those for practice and further research are derived.

Autistic Disorder↗
PubMed1988

The effects of three feedback modes on the ability of normal geriatric individuals to match speaking rate.

The present study investigated the effects of three feedback modes (visual-verbal, verbal-quantitative, and verbal-qualitative) on the ability of 30 normal geriatric individuals to match three different speaking rates (slow, average, and fast). Ten subjects were randomly assigned to each feedback condition. Each subject was instructed to produce the stimulus phrase, Buy Bobby a doughnut, at each of the three speaking rates. Subjects in the visual-verbal mode received both visual feedback of the utterance duration via a PM Trainer and verbal feedback from the experimenter indicating the subject's accuracy in matching the specified speaking rate. Feedback during the verbal-quantitative condition consisted of verbal information indicating the subject's accuracy in matching each speaking rate. The verbal-qualitative condition consisted of verbal feedback relative to the subject's ability to match speaking rate, although the feedback was less precise than in the other conditions. Results suggest that visual-verbal and verbal-quantitative feedback lead to significantly better performance than verbal-qualitative feedback in matching speaking rate, particularly when the task becomes more difficult. These results have implications for the training of a similar task in speech-disordered populations.

Aged↗
PubMed1998

Giving feedback in medical education: verification of recommended techniques.

OBJECTIVE: We investigated naturally occurring feedback incidents to substantiate literature-based recommended techniques for giving feedback effectively. SETTING: A faculty development course for improving the teaching of the medical interview, with opportunities for participants to receive feedback. PARTICIPANTS: Seventy-four course participants (clinician-educators from a wide range of medical disciplines, and several behavioral scientists). MEASUREMENTS AND MAIN RESULTS: We used qualitative and quantitative approaches. Participants provided narratives of helpful and unhelpful incidents experienced during the course and then rated their own narratives using a semantic-differential survey. We found strong agreement between the two approaches, and congruence between our data and the recommended literature. Giving feedback effectively includes: establishing an appropriate interpersonal climate; using an appropriate location; establishing mutually agreed upon goals; eliciting the learner's thoughts and feelings; reflecting on observed behaviors; being nonjudgmental; relating feedback to specific behaviors; offering the right amount of feedback; and offering suggestions for improvement. CONCLUSIONS: Feedback techniques experienced by respondents substantiate the literature-based recommendations, and corrective feedback is regarded as helpful when delivered appropriately. A model for providing feedback is offered.

Adult↗
PubMed1998

Oral versus written feedback in medical clinic.

OBJECTIVE: To determine whether residents perceived oral, face-to-face feedback about their continuity clinic performance as better than a similar, written version. DESIGN: Single-blind, randomized controlled trial. SETTING: Two university-based, internal medicine residency clinics. PARTICIPANTS: All 68 internal medicine and combined program (medicine-pediatrics, medicine-psychiatry, medicine-neurology, and preliminary year) residents and their clinic preceptors. MEASUREMENTS AND MAIN RESULTS: Residents at each program were separately randomized to oral or written feedback sessions with their clinic preceptors. The oral and written sessions followed similar, structured formats. Both groups were later sent questionnaires about aspects of the clinic. Sixty-five (96%) of the residents completed the questionnaire. Eight of the 19 questions dealt with aspects of feedback. A feedback scale was developed from the survey responses to those eight questions (alpha = .86). There were no significant differences in the responses to individual questions or in scale means (p > .20) between the two feedback groups. When each university was analyzed separately, one had a higher scale mean (3.10 vs 3.57, p = .047), but within each university, there were no differences between the oral and written feedback groups (p > .20). CONCLUSIONS: No differences were observed between the oral and written feedback groups. In attempting to provide better feedback to their residents, medical educators may better apply their efforts to other aspects, such as the frequency of their feedback, rather than the form of its delivery.

Clinical Competence↗
PubMed1997

Dynamic cursor gain and tactual feedback in the capture of cursor movements.

Recent research involving a trackball with force feedback has demonstrated that tactile feedback can enhance the acquisition of targets in graphical user interfaces in terms of movement times and errors. The present study seeks to explore the degree to which tactual feedback over a target, in contrast to changes in the display/control gain over the target, influences target acquisition performance. Tactual feedback over a target is felt as a pulling force towards the centre of a target, with a counterforce applied when moving out of the centre. Changes in the cursor gain can be used to create a cursor-catching effect by requiring more movement effort of the control device to leave than to enter the target centre, without increasing the total amount of effort to enter and leave the target area. User movement in entering a target is thus braked by the change in cursor gain. Results of an experiment indicated that target acquisition performance was generally higher in the tactual feedback condition, followed by cursor gain feedback, in comparison with no-cursor gain feedback. User interface design issues as related to gain feedback in visual interfaces and tactual feedback over targets are considered.

Adult↗
PubMed1990

Concurrent augmented feedback and isometric force generation during familiar and unfamiliar muscle movements.

To evaluate the effect of concurrent augmented feedback on isometric force output during familiar and unfamiliar muscle movements, 18 men and 21 women, 18 to 23 years of age, completed two isometric exercises: flexion of the thumb (a familiar muscle movement) and abduction of the fifth digit (an unfamiliar movement). The exercises consisted of 10 maximum voluntary isometric contractions lasting 10 s each and separated by 10-s intertrial rest intervals. Concurrent visual feedback was provided during alternate contractions. The order of exercises and trials for feedback was randomly assigned and balanced over subjects. Peak force output during abduction of the fifth digit was significantly (p less than or equal to .01) greater with (4.4 +/- 0.29 kg) than without feedback (4.1 +/- 0.26 kg). Feedback did not influence (p greater than .05) peak force output during thumb flexion (23.2 +/- 1.09 kg vs 22.5 +/- 1.05 kg). Muscular fatigue was more pronounced during thumb flexion without feedback (18.4 +/- 1.17%) than when feedback was provided (11.8 +/- 1.36%). These data suggest that fatigue may increase the effect of feedback on force generation during familiar muscular movements. To obtain maximal isometric force measures during strength testing, augmented feedback should be provided.

Adolescent↗
PubMed2005

Self-controlled feedback is effective if it is based on the learner's performance.

The study follows up on the contention that self-controlled feedback schedules benefit learning because they are more tailored to the performers' needs than externally controlled feedback schedules (Chiviacowsky & Wulf, 2002). Under this assumption, one would expect learning advantages for individuals who decide whether they want to receive feedback after a trial rather than before a trial. Participants practiced a sequential timing task, and all could decide the trials on which they received feedback. One group ("self-after") decided after every trial whether they wanted to receive feedback for that trial while another group ("self-before") made that decision before each trial The self-after group showed learning benefits on a delayed transfer test (novel absolute timing requirements) with regard to overall timing and relative-timing accuracy. Thus, self-controlled feedback was more effective when the learner could make a decision about receiving feedback after the trial. This seems to support the view that self-controlled feedback benefits learning, because learners can make a decision about feedback based on their performance on a given trial.

Adult↗
PubMedDate not supplied

Development of forward and feedback connections between areas V1 and V2 of human visual cortex.

We have determined the sequence in which forward connections between visual cortical areas V1 and V2, and feedback connections between V2 and V1 develop in humans. For this purpose Dil was injected into V1 and V2 of postmortem brains of different pre- and postnatal ages. The laminar distribution of labeled fibers and cell bodies in V1 and V2 indicates that forward and feedback connections emerge shortly before birth. The development of both pathways proceeds over several postnatal months such that the laminar termination pattern of forward connections appears relatively mature before feedback connections reach their mature form. At 37 weeks of gestation both forward and feedback connections originate exclusively from deep-layer neurons, which extend axons in deep layers only. By 9 d postnatal, forward connections from V1 to V2, in addition to layers 5 and 6, also arise from neurons in layer 4B of V1. At this stage for the first time forward fibers enter layer 4 at the topographically appropriate location of V2. At 9 d postnatal most feedback fibers from V2 still occupy deep layers of V1 but many, through interstitial growth, elaborate vertical sprouts at regular intervals along the length of horizontal axons. As feedback connections mature, distal segments of horizontal axons are pruned back to branch points and fibers assume L-shaped configurations. By 7 weeks of age forward fibers from V1 enter V2 through deep and superficial layers and provide input to layers 3 and 4. At this stage feedback fibers from V2 have entered layer 4B of V1. By 4 months of age forward connections have assumed all the laminar characteristics of mature connections; that is, they arise from layers 2/3, 4B, 5, and 6 of V1, and terminate in layers 3 and 4 of V2. In sharp contrast, at 4 months of age feedback connections to V1 are still immature, showing terminations in layers 4B, 5, and 6 but no input to layer 2/3. The protracted postnatal emergence of feedback connections is similar to that of local long-range connections within layer 2/3 of V1 (Burkhalter et al., 1993). Since both of these circuits are thought to provide information about the context in which objects are seen, it is interesting to speculate that the late onset of texture segmentation in infants (Atkinson and Braddick, 1992; Sireteanu and Rieth, 1992) may be related to the postnatal maturation of specific intracortical circuits.

Carbocyanines↗
PubMed1998

The effect of a drug and supply cost feedback system on the use of intraoperative resources by anesthesiologists.

UNLABELLED: We performed a randomized, prospective study to evaluate the use of a written feedback system in reducing the intraoperative costs of drugs and supplies used by anesthesiologists. Over 6 mo, 27 anesthesiology residents were randomized to feedback and control groups for their rotations in neurosurgical anesthesia. We recorded the cost of drugs and supplies for three procedures: carotid endarterectomy, lumbar decompression, and cervical decompression. For each study case, members of the feedback group received a written cost analysis showing their performance relative to the departmental average. Members of the feedback group had significantly lower costs for carotid endarterectomies ($79.98 +/- $15.20 vs $97.59 +/- $21.53) and for lumbar decompressions ($56.72 +/- $16.49 vs $76.05 +/- $20.11). The source of savings included lower use rates for propofol and etomidate and for patient warming devices. Analysis of data from recovery areas revealed a trend toward lower patient temperature in lumbar procedures performed by the feedback group. Three months after the feedback period, we collected a follow-up data set in the absence of feedback. This revealed a significant rebound in overall cost by the feedback group for both carotid endarterectomies and lumbar surgery. IMPLICATIONS: This is the first randomized, prospective evaluation of a cost management system in anesthesia. Using resident anesthesiologists, we showed that the written feedback of individualized performance data can be used to lower the overall cost of intraoperative drugs and supplies used for an anesthetic in the absence of mandated clinical guidelines.

Anesthesiology↗
PubMed2006

Value of debriefing during simulated crisis management: oral versus video-assisted oral feedback.

BACKGROUND: The debriefing process during simulation-based education has been poorly studied despite its educational importance. Videotape feedback is an adjunct that may enhance the impact of the debriefing and in turn maximize learning. The purpose of this study was to investigate the value of the debriefing process during simulation and to compare the educational efficacy of two types of feedback, oral feedback and videotape-assisted oral feedback, against control (no debriefing). METHODS: Forty-two anesthesia residents were enrolled in the study. After completing a pretest scenario, participants were randomly assigned to receive no debriefing, oral feedback, or videotape-assisted oral feedback. The debriefing focused on nontechnical skills performance guided by crisis resource management principles. Participants were then required to manage a posttest scenario. The videotapes of all performances were later reviewed by two blinded independent assessors who rated participants' nontechnical skills using a validated scoring system. RESULTS: Participants' nontechnical skills did not improve in the control group, whereas the provision of oral feedback, either assisted or not assisted with videotape review, resulted in significant improvement (P < 0.005). There was no difference in improvement between oral and video-assisted oral feedback groups. CONCLUSIONS: Exposure to a simulated crisis without constructive debriefing by instructors offers little benefit to trainees. The addition of video review did not offer any advantage over oral feedback alone. Valuable simulation training can therefore be achieved even when video technology is not available.

Adult↗
PubMedDate not supplied

360-feedback in health care management: a field study.

In recent years, organizations representing all types of industries, including health care, have adopted the 360-feedback approach with the goal of strengthening leader performance. But while 360-feedback enjoys a high level of face validity, current research shows that it is not problem-free and often fails to achieve its goals without proper development and implementation. This research, conducted in a large public hospital, surveyed the top management team of 49 executives who participated in a 360-feedback project beginning in February 2001. The survey, designed to solicit opinions about the effectiveness of the 360-feedback project, resulted in several recommendations to improve the process: One, both mentors and participants (raters and those rated) should be formally trained to improve the feedback process. Two, participants--both raters and those rated--should be significantly involved in 360-feedback planning and development efforts. Three, the 360-feedback process should be linked to hospital objectives. Four, the 360-feedback process should focus not only on interpersonal issues but departmental and organizational goals as well. First and foremost, our findings show that regardless of how popular a management development program may be, no technique for improving management and organizational effectiveness, including 360-feedback, will work unless properly designed and implemented.

Feedback↗
PubMed2005

Delayed excitatory and inhibitory feedback shape neural information transmission.

Feedback circuitry with conduction and synaptic delays is ubiquitous in the nervous system. Yet the effects of delayed feedback on sensory processing of natural signals are poorly understood. This study explores the consequences of delayed excitatory and inhibitory feedback inputs on the processing of sensory information. We show, through numerical simulations and theory, that excitatory and inhibitory feedback can alter the firing frequency response of stochastic neurons in opposite ways by creating dynamical resonances, which in turn lead to information resonances (i.e., increased information transfer for specific ranges of input frequencies). The resonances are created at the expense of decreased information transfer in other frequency ranges. Using linear response theory for stochastically firing neurons, we explain how feedback signals shape the neural transfer function for a single neuron as a function of network size. We also find that balanced excitatory and inhibitory feedback can further enhance information tuning while maintaining a constant mean firing rate. Finally, we apply this theory to in vivo experimental data from weakly electric fish in which the feedback loop can be opened. We show that it qualitatively predicts the observed effects of inhibitory feedback. Our study of feedback excitation and inhibition reveals a possible mechanism by which optimal processing may be achieved over selected frequency ranges.

Action Potentials↗