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PubMed2000

Differences in use and impact of computer-tailored dietary fat-feedback according to stage of change and education.

Computer-tailored written nutrition education has been found to be more effective in motivating people to reduce their consumption of fat than traditional written information. The present study aimed to test whether this innovative nutrition education intervention is also suitable for people with low motivation to change and low education among a self-selected sample of 699 adults. Computer-tailored feedback proved to be more effective in motivating precontemplators to proceed towards fat reduction than general information. Higher appreciation and use of the computer-tailored fat-feedback was found among respondents in contemplation than in other stages. No difference in impact of computer-tailored fat-feedback on fat intake was found between educational groups. Respondents with low education were more positive about how interesting and how personally relevant the tailored letters were. It was concluded that printed computer-tailored fat-feedback can be applied successfully to motivate precontemplators and people with low education to (consider to) reduce their fat intake.

Adult↗
PubMed2000

Detection of nuclear resonance signals: modification of the receiver operating characteristics using feedback.

The performance of a nuclear resonance detection system can be quantified using binary detection theory. Within this framework, signal averaging increases the probability of a correct detection and decreases the probability of a false alarm by reducing the variance of the noise in the average signal. In conjunction with signal averaging, we propose another method based on feedback control concepts that further improves detection performance. By maximizing the nuclear resonance signal amplitude, feedback raises the probability of correct detection. Furthermore, information generated by the feedback algorithm can be used to reduce the probability of false alarm. We discuss the advantages afforded by feedback that cannot be obtained using signal averaging. As an example, we show how this method is applicable to the detection of explosives using nuclear quadrupole resonance.

Algorithms↗
PubMed2001

Provider feedback improves adherence with AHCPR Smoking Cessation Guideline.

BACKGROUND: This study evaluated the effect of primary care providers' adherence with the AHCPR Smoking Cessation Guideline after receiving a multicomponent intervention. METHODS: A quasi-experimental study with one intervention and one control team was conducted in a southeastern Veterans Affairs Medical Center primary care setting. During phase I, chart reviews were conducted to measure baseline provider adherence and documentation of the four A's (ask, advise, assist, arrange). In phase II, the intervention team received a single educational session on the AHCPR Guideline, four A's, and tobacco dependence treatment. This was followed by chart reviews of patients seen 4 to 8 weeks after the educational intervention to measure provider adherence and documentation of the four A's. During phase III, the intervention team received individual and team feedback from the chart reviews in phases I and II and booster education on the AHCPR Guideline. Chart reviews were conducted from patient visits 4 to 8 weeks after the feedback and booster education to determine provider adherence and documentation of the four A's. RESULTS: A nested repeated measures two-factor analysis of variance was performed for each of the following outcomes: ask, advise, assist, and arrange. Data analyses revealed that both the control and the intervention teams had 100% compliance in asking the patient about smoking status. There was a prestudy implementation of the vital sign stamp that included smoking status in this setting. Education on tobacco dependence and the AHCPR Guideline had no significant impact on provider performance with the advisement, assistance, and arrangement of follow-up. However, significant improvements occurred in the intervention team in the advisement (P = 0.05), assistance (P = 0.001), and arrangement of follow-up (P = 0.001) phase after individual and team feedback was provided. This research supports the fact that feedback impacts individuals and team performances and facilitated positive system changes to improve provider adherence with the AHCPR recommendations in treating tobacco dependence.

Feedback↗
PubMed1994

Feedback inhibition in the cat's lateral geniculate nucleus.

Feedback inhibition is generally believed to be a ubiquitous feature of brain circuitry, but few specific instances have been documented. An example in cats is the supposed feedback circuit involving relay cells of the lateral geniculate nucleus and cells of the perigeniculate nucleus (a part of the thalamic reticular nucleus): geniculate relay cells innervate the perigeniculate nucleus, which, in turn, provides an inhibitory, GABAergic projection back to the lateral geniculate nucleus. However, feedback inhibition at the single-cell level requires that a given perigeniculate cell project back onto the same geniculate relay cell that innervates it. We probed for this in an in vitro slice preparation of the cat's lateral geniculate nucleus. We evoked a single action potential in a geniculate cell via a brief, depolarizing pulse delivered through an intracellular recording electrode and looked for any evoked hyperpolarizations. For 6 of the 36 geniculate cells tested, we observed a long-lasting hyperpolarization after the action potential, and much of this was eliminated by application of bicuculline, suggesting synaptically activated inhibitory postsynaptic potentials. We interpreted this to be clear evidence that a given neuron may inhibit itself via circuitry mediating feedback inhibition in the cat's lateral geniculate nucleus.

Animals↗
PubMed1993

Ocular limit cycles induced by delayed retinal feedback.

Lisberger's and Robinson's models of smooth pursuit predict very different results from altering retinal feedback delay. We have therefore investigated the effects of increasing the retinal feedback time delay in three normal human subjects by means of an artificial feedback paradigm. When additional delays were incorporated into the retinal feedback path a threshold was reached beyond which the eye exhibited sustained self-excited oscillations or "limit cycles". The oscillation period increased linearly (as the added delay was increased) with slopes ranging from 1.41 to 1.6 with zero-delay intercepts of between 212 and 306 ms. Contrary to our experimental findings the Robinson and Lisberger models predict that the plot of oscillation period against added delay should have a slope of 3.4 and 2.7 and an intercept of 479 and 554 ms, respectively. Neither model produced comparable limit cycles, both being unstable at delays greater than 280 ms. Our results imply that the models of smooth pursuit need to incorporate predictive control.

Adult↗
PubMed1989

Paw-shake responses with joint immobilization: EMG changes with atypical feedback.

To determine the effects of atypical motion-related feedback on motor patterns of the paw shake, EMG patterns of selected flexor and extensor muscles were recorded under four conditions of joint immobilization (hip and ankle alone, hip-knee, hip-knee-ankle) and compared to responses evoked in the freely-moving hindlimb of the chronic-spinal cat. With only the ankle joint casted, paw shaking was easily evoked by applying tape to the paw, and cyclic characteristics were not altered. However, under the three conditions with hip-joint immobilization (hip alone, hip-knee, hip-knee-ankle), responses were difficult to obtain, and if elicited, the number of cycles within a response decreased and cycle periods were prolonged. The temporal organization of consecutive cycles, however, was not altered by immobilization of any joint(s). Ankle (LG) and hip (GM) extensor activity was relatively unaffected by conditions of joint immobilization. In contrast, hip flexor (IP) and knee extensor (VL) bursts were often absent under all three conditions of hip-joint immobilization, and if present, VL burst durations decreased under the casted hip-knee-ankle condition, while the onset of IP activity occurred early in the cycle with prolonged bursts under casted ankle and casted hip-knee-ankle conditions. The coactivity of the knee extensor (VL) and ankle flexor (TA) was disrupted by conditions of hip-joint immobilization: VL onset was dissociated from TA onset and coincident with LG onset. These results suggest that motion-related feedback from the hip joint is particularly important in the initiation, cycle frequency, and the number of cycles of paw-shake responses. The presence of atypical motion-dependent feedback from the hip joint altered activity of knee and ankle anterior muscles, while motion-dependent feedback from the ankle joint changed activity of the anterior hip muscle. Moreover, the results suggest a differential control of posterior and anterior muscles of the hindlimb, consistent with paw-shake limb dynamics.

Animals↗
PubMed1975

Maintenance of feedback regulation of filtration dynamics in the absence of divalent cations in the lumen of the distal tubule.

In the present experiments we have studied the hypothesis that the feedback responses of glomerular capillary pressure and glomerular filtration rate to elevated distal fluid delivery depend to some extent on the luminal concentration of calcium or magnesium [1]. Loops of Henle were therefore perfused with the following solutions which were designed to yield wide variations of distal divalent cation concentration: 1. Ringer, 2. 140mM NaCl, 3. 125mM NaCl + 10mM CaCl2, 4. 125 mM NaCl + 10 mM MgCl2, 5. 125 mM NaCl + 10 mM Na citrate, and 6. 125 mM NaCl + 10 mM EDTA. During orthograde perfusion with these solutions stop flow pressure (SEP) and early proximal flow rate (EPFR) were measured in each nephron at perfusion rates of 0, 15, 30, and 45 nl/min. We found that perfusion with solutions 2 to 6 did not significantly modify the flow induced change of SFP or EPFR observed during Ringer perfusion. To expose the macula densa cells to chemically well defined solutions loops of Henle were retrogradely perfused from the distal tubule and EPFR was measured in a given nephron with and without perfusion. Identical reductions of EPFR were induced by retrograde perfusions with 140 mM NaCl, 125 mM NaCl + 10 mM CaCl2, and 125 mM NaCl + 10 mM EDTA. Furthermore, an almost complete blunting of the feedback response was noted during retrograde perfusion with 25 mM NaCl. Addition of 5 mM CaCl2 failed to restore the feedback reaction. These results do not support the concept that luminal divalent cations participate in the initiation of tubulo-glomerular feedback responses.

Animals↗
PubMed1981

Effects of discrete visual feedback on the electrodermal control of a stressful situation.

Two groups of human volunteers received three sessions of discriminated avoidance and punishment with the skin resistance response (SRR) as the operant. During each session one group (feedback) received three 6-8-min periods of Sidman avoidance of a 1.5-mA shock (R-S = 40 sec, S-S = 35 sec) mixed with three periods of punishment with a 20-sec time-out after each period. The avoidance and punishment periods were signaled by red and green lights, and a circle appeared superimposed on the discriminative stimuli for the duration of a criterion response. A second group (no feedback) received the same conditions as the feedback group except that no circle appeared. Instructions to the subject were not informative regarding experimental events. Subjects made significantly more SRR's during avoidance, a contingency in which responding prevented shock, than during punishment, a contingency in which responding produced shock. A reliable four-way interaction suggested that the feedback stimulus curtailed a tendency for avoidance response rate to diminish within and between experimental sessions. The data are considered as evidence for electrodermal (autonomic) control of two different stressful situations, and the potential value of the paradigm for establishing tonic autonomic arousal and suppression is considered.

Avoidance Learning↗
PubMed1996

The diluting effect of medical work groups on feedback efficacy in changing physician's practice.

Feedback intervention has been advocated as a successful method to modify the way that physicians practice medicine. However, most studies concerned with modifying physician profiles have focused on interns and residents. The results presented here concern regular staff and therefore provide a better basis for generalization. Over a 2.5-year period, we analyzed the use of clinical resources by physicians practicing in four medical specialties in two hospitals. Hierarchical multiple regression models were used to control case mix in order to identify the specific effects attributable to feedback. The information failed to modify the physicians' practice profiles. Our results suggest that this failure is related to the organization of inpatient medical practice as a group effort. This mode of practice has a negative effect on feedback efficacy. First, it weakens one of the main feedback mechanisms, that is personal identification with the data. Second, it probably generates mutual adjustment among physicians, thus eliminating practice variations at the source.

Adult↗
PubMed1995

Effects of enteral feedback inhibition on motility, luminal flow, and absorption of nutrients in proximal gut of minipigs.

We wanted to clarify whether the postprandial intestinal feedback control activated by nutrients in the distal gut exerts different effects on motility, transit of digesta, and absorption of nutrients in the proximal gut. Additionally, interrelationships among motility, transit, and absorption were to be elucidated because these relationships have only been investigated in the fasted state. In five minipigs, a 150-cm segment of the proximal jejunum was isolated by two cannulas. Motility of the jejunal segment was recorded by multiple strain gauges and analyzed by computerized methods. Markers (Cr- and Cu-EDTA) were used for the measurement of the flow rate, transit time, and absorption of nutrients. After a meal, the test segment was perfused with 2 kcal/min of an elemental diet over a period of 90 min. A feedback inhibition was activated by infusion of nutrients into the midgut at rates of 1-4 kcal/min. Saline was infused as control. With increasing energy loads infused into the midgut, the motility index and the length of contraction waves decreased, whereas the incidence of stationary contractions increased, ie, the motility changed from a propulsive to a segmenting pattern. These modulations of motility were associated with a linear decrease in the flow rate and a linear increase in transit time. Flow and transit were linearly correlated with each other. Additionally, the reduction in flow rate and the delay in luminal transit were associated with a linear increase in the absorption of nutrients. However, the increase in absorption induced by the feedback mechanism was small (7.3-13.4%) compared to the marked inhibition of the motility parameters (54-64%), the flow rate (59%), and the delay of transit (5.8-fold). Feedback control primarily modulated motor patterns and luminal flow, whereas the small increase in absorption was only a side effect due to the longer contact time of the nutrients with the mucosa.

Animals↗
PubMedDate not supplied

Participation of gamma-aminobutyric acid in the negative feedback mechanisms of the hypothalamohypophyseotesticular complex.

It is known that gamma-aminobutyric acid (GABA) participates in the regulation of the secretion of many adenohypophyseal hormones [2, 9]. In addition, GABAergic mechanisms may be involved in the regulation of testosterone-dependent aggressive [5] and sexual [8] behavior. A substantial number of studies suggest that GABA and its receptors are capable of participating in the regulation of the secretions of luteinizing hormone (LH). However, its role in this process is not entirely clear, since according to the data of various authors, GABA exerts both inhibitory and activating influences on the secretion of LH [3, 12]. Still less is known of the role of GABA and its receptors in the regulation of the secretion of LH by the negative feedback mechanism, which has been studied in bilaterally castrated rats [3]. However, such a model offers the possibility of investigating only a separate link of this mechanism which regulates the hypothalamohypophyseotesticular complex (HHTC). With regard to the study of the neurochemical regulation of the integral negative feedback system, the use of unilaterally castrated rats is more appropriate for this purpose. In such animals the compensation of the insufficiency of androgens is determined by negative feedback stimulation, and not by the administration of exogenous steroids. In addition, the level of testosterone in the peripheral blood more adequately reflects the state of this mechanism than the level of the gonadotropins [7]. However, the role of GABA and its receptors in the regulation of the integral negative feedback mechanism of the HHTC, so far as we know, remains entirely unstudied. This was in fact the purpose of the present study.

Animals↗
PubMed2003

Quantitative analyses of principal and secondary compound parieto-occipital feedback pathways in cat.

The purpose of our study was to quantify the magnitude of principal and secondary pathways emanating from the middle suprasylvian (MS) region of visuoparietal cortex and terminating in area 18 of primary visual cortex. These pathways transmit feedback signals from visuoparietal cortex to primary visual cortex. (1) WGA-HRP was injected into area 18 to identify inputs from visual structures. In terms of numbers of neurons, feedback projections to area 18 from MS sulcal cortex (areas PMLS, AMLS and PLLS) comprise 26% of inputs from all visual structures. Of these neurons, between 21% and 34.9% are located in upper layers 2-4 and the dominant numbers are located in deep layers 5 and 6. Areas 17 (11.8%) and 19 (11.2%) provide more modest cortical inputs, and another eight areas provide a combined total of 4.3% of inputs. The sum of neurons in all subcompartments of the lateral geniculate nucleus (LGN) accounts for another 34.8% of the input to area 18, whereas inputs from the lateral division of the lateral-posterior nucleus (LPl) account for the final 11.9%. (2) Injection of tritiated-((3)H)-amino acids into MS sulcal cortex revealed substantial direct projections from MS cortex that terminated in all layers of area 18, but with a markedly lower density in layer 4. Projections from MS cortex to both areas 17 and 19 are of similar density and characteristics, whereas those to other cortical targets have very low densities. Quantification also revealed minor-to-modest axon projections to all components of LGN and a massive projection throughout the LP-Pul complex. (3) Superposition of the labeled terminal and cell fields identified secondary, compound feedback pathways from MS cortex to area 18. The largest secondary pathway is massive and it includes the LPl nucleus. Much more modest secondary pathways include areas 17 and 19, and LGN. The relative magnitudes of the secondary pathways suggest that the one through LPl exerts a major influence on area 18, whereas the others exert more modest or minor influences. MS cortex in the contralateral hemisphere also innervates area 18 directly. These data are important for interpreting the impact of deactivating feedback projections from visuoparietal cortex on occipital cortex.

Animals↗
PubMed2004

Augmented visual feedback increases finger tremor during postural pointing.

Physiological tremor in the upper limb of eight adults was examined during the performance of a unilateral pointing task under conditions where the visual feedback, limb used and target size were altered. All subjects were required to aim a hand-held laser pointer at a circular target 5.5 m away with the goal of keeping the laser emission within the centre of the target. Visual feedback was defined as either normal vision (NV) of their limb tremor, where the laser was switched off, or augmented vision (AV) where the laser was switched on. Postural tremor from the segments of the upper limb, forearm muscle EMG activity, and target accuracy measures were recorded and analysed in the time and frequency domains. Accuracy-tremor relations were assessed using cross correlation and linear regression. Results revealed a high degree of similarity in the general pattern of the tremor output seen for each limb segment across conditions with only scalar (amplitude) changes being seen as a function of the different constraints imposed. For any single condition the tremor amplitude increased from proximal to distal segments. The frequency profile for the tremor in any segment displayed two prominent frequency peaks (at 2-4 Hz and 8-12 Hz). A third, higher frequency peak (18-22 Hz) was observed in the index fingers only. Across all conditions significant coupling relations were observed only between the hand-finger and forearm-upper arm segment pairs. Altering the visual feedback was shown to have the greatest effect on limb tremor with increased tremor and EMG activity and decreased coupling being seen under AV conditions. In trying to reduce tremor output when the augmented feedback was provided novice subjects instead increased muscle activity which resulted in increased tremor. Overall these results indicate that the physiological tremor output observed in neurologically normal subjects is not simply the product of intrinsic oscillations but is influenced by the nature of the task being performed.

Adult↗
PubMed2005

Humans use continuous visual feedback from the hand to control both the direction and distance of pointing movements.

Vision of the hand during reaching provides dynamic feedback that can be used to control movement. We investigated the relative contributions of feedback about the direction and distance of the hand relative to a target. Subjects made pointing movements in a 3-D virtual environment, in which a small sphere provided dynamic visual feedback about the position of their unseen fingertip. On a subset of trials, the position of the virtual fingertip was smoothly shifted by 2 cm during movement, either (1) in the direction of movement, which would require adjustments to the distance moved, or (2) orthogonal to the direction of movement, which would require adjustments to the direction moved. Despite not noticing the perturbations, subjects adjusted their movements to compensate for both types of visual shifts. Corrective responses to direction perturbations were observed within 117 ms, and response latencies were invariant to movement speed and perturbation onset time. Initial corrections to distance perturbations were smaller and appeared after longer delays of 130-200 ms, and both the speed and magnitude of responses were reduced for early onset perturbations. Simulations of a feedback control model that optimally integrates visual information over time show that the results can be explained by differences in the sensory noise levels in the visual dimensions relevant for direction and distance control.

Adaptation, Physiological↗
PubMed1998

Sinusoidal forearm tracking with delayed visual feedback. II. Dependence of the relative phase on the relative delay.

The influence of delayed visual feedback on the phase relationships between target and response signal during a sinusoidal tracking task was analysed in five normal subjects. Target frequency was varied systematically between 0.3 and 1.5 Hz, and the delay between 0 and 120% of the target cycle duration. For each subject, 63 trials were recorded. Phase parameters (relative phase, absolute relative phase and percentage of positive relative phases) revealed a clear dependence on relative delay but not on target frequency. With relative delays close to 0 and 100% of the target cycle duration, subjects successfully tracked the target signal with a small phase lag. With delays in the 30-90% range, larger phase differences were observed. Furthermore, the (delayed) response signal usually preceded the target signal in this delay range. These findings provide further evidence for a dependence of tracking error on external delays in the visual feedback loop, and indicate that delays of about 50% of the movement cycle are more difficult to handle than are smaller or larger delays. The results are discussed with regard to the influence of different control strategies (feedback, feedforward) and different types of feedback (such as vision and proprioception) on motor control.

Adult↗
PubMed1998

Changes in the force-sharing pattern induced by modifications of visual feedback during force production by a set of fingers.

We investigated force-sharing among three fingers which acted in parallel and produced ramp profiles of total force from zero to the maximal voluntary force. The feedback to the subject was provided by a visual signal on the monitor and could correspond to the sum of forces of all the fingers or to the sum of forces of two fingers, while the force of the third finger was added with a coefficient 2 or 0.5. If the subjects did not know about the distorted feedback, they showed a template-sharing pattern within the whole range of total force values. This pattern did not depend on which finger force was multiplied and by which coefficient. If the subjects knew in advance how the feedback signal would be calculated, they tried to perform the task using either only the finger whose force was multiplied by 2 or two fingers when the force of the third one was multiplied by 0.5. Further into the trial, however, they were unable to track the ramp pattern using only one or two fingers and demonstrated a search activity that could continue until the end of the trial or lead eventually to a three-finger sharing pattern similar to the template pattern used in cases of undistorted feedback. We conclude that the limited number of preferred sharing pattern within the studied task reflects an organization of the fingers into a structural unit (involving one, two, or all three fingers) by the central nervous system. The availability of structural units defines the presence of stable solutions available for the system.

Adult↗
PubMed2001

Role of cortical feedback in the receptive field structure and nonlinear response properties of somatosensory thalamic neurons.

Previous studies have suggested that the descending pathway from the primary somatosensory (SI) cortex to the ventral posterior nucleus of the thalamus has only a mild facilitative influence over thalamic neurons. Given the large numbers of corticothalamic terminations within the rat somatosensory thalamus and their complex topography, we sought to examine the role of corticothalamic feedback in the genesis of spatiotemporal receptive fields and the integration of complex tactile stimuli in the thalamus. By combining focal cortical inactivation (produced by microinjection of the GABA(A) agonist muscimol), with chronic multielectrode recordings, we observed that feedback from the rat SI cortex has multiple influences on its primary thalamic relay, the ventral posterior medial (VPM) nucleus. Our data demonstrate that, when single-whisker stimuli were used, the elimination of cortical feedback caused significant changes in the spatiotemporal structure of the receptive fields of VPM neurons. Cortical feedback also accounted for the nonlinear summation of VPM neural responses to simultaneously stimulated whiskers, in effect "linearizing" the responses. These results argue that the integration and transmission of tactile information through VPM are strongly influenced by the state of SI cortex.

Animals↗
PubMed2003

Traveling-wave pattern generator controls movement and organization of sensory feedback in a spinal cord model.

A traveling wave in a two-dimensional spinal cord model constitutes a stable pattern generator for quadruped gaits. In the context of the somatotopic organization of the spinal cord, this pattern generator is sufficient to generate stable locomotive limb trajectories. The elastic properties of muscles alone, providing linear negative feedback, are sufficient to stabilize stance and locomotion in the presence of perturbative forces. We further show that such a pattern generator is capable of organizing sensory processing in the spinal cord. A single-layer perceptron was trained to associate the sensory feedback from the limb (coding force, length, and change of length for each muscle) with the two-dimensional activity profile of the traveling wave. This resulted in a well-defined spatial organization of the connections within the spinal network along a rostrocaudal axis. The spinal network driven by peripheral afferents alone supported autonomous locomotion in the positive feedback mode, whereas in the negative feedback mode stance was stabilized in response to perturbations. Systematic variation of a parameter representing the effect of gamma-motor neurons on muscle spindle activity in our model led to a corresponding shift of limb position during stance and locomotion, resulting in a systematic displacement alteration of foot positions.

Feedback, Physiological↗