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PubMed2004

Modeling direct positive feedback between predators and prey.

Predators can have positive impacts on their prey through such mechanisms as nutrient mineralization and prey transport. These positive feedbacks have the potential to change predictions based on food web theory, such as the assertion that enrichment is destabilizing. We present a model of a simple food web, consisting of a resource, a consumer, and its predator. We assume that the predator has a direct positive effect on the consumer, by increasing the rate at which the consumer acquires resources. We consider two cases: the feedback strength is a saturating function of predator density, or it is proportional to the encounter rate between predators and prey. In both cases, the positive feedback is stabilizing, delaying or preventing the onset of oscillations due to enrichment. Positive feedback can introduce an Allee effect for the predator population, yielding multiple stable equilibria. Strong positive feedback can yield counterintuitive results such as a transient increase in consumer density following the introduction of predators, and a decrease in the resource pool following enrichment.

Animals↗
PubMed2004

Vicious circles: positive feedback in major evolutionary and ecological transitions.

Evolutionary biologists and ecologists often focus on equilibrium states that are subject to forms of negative feedback, such as optima for phenotypic traits or regulation of population sizes. However, recent theoretical and empirical studies show how positive feedback can be instrumental in driving many of the most important and spectacular processes in evolutionary ecology, including the evolution of sex and genetic systems, mating systems, life histories, complex cooperation in insects and humans, ecological specialization, species diversity, species ranges, speciation and extinction. Taken together, this work suggests that positive feedback is more common than is generally appreciated, and that its self-reinforcing dynamics generate the conditions for changes that might otherwise be difficult or impossible for selection or other mechanisms to achieve. Testing for positive feedback requires analysing each causal link in feedback loops, tracking genetic, character and population-dynamic changes across generations, and elucidating the conditions that can result in self-reinforcing change.

Journal Article↗
PubMed2001

The impact of sucrose-derived unconditioned and conditioned negative feedback on the microstructure of ingestive behavior.

We describe at the microstructural level the impact of unconditioned and conditioned negative feedback on the licking behavior of the rat. Seven groups of rats were trained to ingest one of seven different concentrations of sucrose (0.025, 0.05, 0.1, 0.2, 0.4, 0.6, and 0.8 M sucrose) under real-feeding conditions until intake was stable. They were then given three sham-feeding tests with the same solution. We compared the size of the clusters (SC) and number of clusters (NC) during the 17-min period when intake rate was declining in the real-feeding test with SC and NC during the corresponding 17-min period in the following sham-feeding test. Intake increased significantly over the three sham-feeding tests with the three highest concentrations, indicating the extinction of conditioned negative feedback. With these three solutions, we compared the microstructure of licking behavior in the first with that in the third sham-feeding test to determine if conditioned negative feedback affected SC or NC or both. The effect of both unconditioned and conditioned negative feedback on licking behavior was to decrease the NC without significantly affecting their size. We conclude that negative feedback derived from the accumulation of sucrose in the gastrointestinal tract decreases the probability of initiating a bout of licking during a pause. It has no effect on the ability to continue a bout of licking once it has begun.

Animals↗
PubMedDate not supplied

The effect of standardized patient feedback in teaching surgical residents informed consent: results of a pilot study.

PURPOSE: The purpose of this pilot study was to determine the effectiveness of using feedback from a standardized patient (SP) to teach a surgical resident (SR) informed consent (IC) protocol. METHODS: Four general case types of increasing difficulty were tested in a longitudinal experimental design format. The four types of cases were appendectomy, cholecystectomy, colorectal cancer, and breast cancer. Eight SRs of varying years of completion in medical school served as subjects-four in the experimental group (received performance feedback from an SP) and four in the control group (received no SP feedback). Both the control and experimental groups participated in two patient encounters per case type. The first patient encounter served as the pretest, and the second patient encounter was the posttest. In each encounter, an SP rated the resident on 14 measures using an open-ended seven-point rating scale adopted and modified from the Brown University Interpersonal Skill Evaluation (BUISE). Each resident also reviewed a videotape of an expert giving IC between pretest and the posttest for basic instructional protocol. Random stratified sampling was used to equally distribute the residents by postgraduate years. A total of 16 SPs were used in this study. All patient/SR encounters were videotaped. RESULTS: There was a statistically significant overall change--pretest to posttest and across cases (p = 0.001). The group effect was statistically significant (p = 0.000), with the experimental group averaging about 10 points greater than the control group. CONCLUSIONS: Standardized patient feedback is an effective modality in teaching surgical residents informed consent protocol. This conclusion is tentative, due to the limitations of sample size. The results of this study support continued research on the effects of standardized patient feedback to teach informed consent to surgical residents.

General Surgery↗
PubMed2002

Significance of auditory and kinesthetic feedback to singers' pitch control.

An accurate control of fundamental frequency (F0) is required from singers. This control relies on auditory and kinesthetic feedback. However, a loud accompaniment may mask the auditory feedback, leaving the singers to rely on kinesthetic feedback. The object of the present study was to estimate the significance of auditory and kinesthetic feedback to pitch control in 28 students beginning a professional solo singing education. The singers sang an ascending and descending triad pattern covering their entire pitch range with and without masking noise in legato and staccato and in a slow and a fast tempo. F0 was measured by means of a computer program. The interval sizes between adjacent tones were determined and their departures from equally tempered tuning were calculated. The deviations from this tuning were used as a measure of the accuracy of intonation. Statistical analysis showed a significant effect of masking that amounted to a mean impairment of pitch accuracy by 14 cent across all subjects. Furthermore, significant effects were found of tempo as well as of the staccato/legato conditions. The results indicate that auditory feedback contributes significantly to singers' control of pitch.

Adult↗
PubMed2003

Pitch matching accuracy of trained singers, untrained subjects with talented singing voices, and untrained subjects with nontalented singing voices in conditions of varying feedback.

At a physiological level, the act of singing involves control and coordination of several systems involved in the production of sound, including respiration, phonation, resonance, and afferent systems used to monitor production. The ability to produce a melodious singing voice (eg, in tune with accurate pitch) is dependent on control over these motor and sensory systems. To test this position, trained singers and untrained subjects with and without expressed singing talent were asked to match pitches of target pure tones. The ability to match pitch reflected the ability to accurately integrate sensory perception with motor planning and execution. Pitch-matching accuracy was measured at the onset of phonation (prephonatory set) before external feedback could be utilized to adjust the voiced source, during phonation when external auditory feedback could be utilized, and during phonation when external auditory feedback was masked. Results revealed trained singers and untrained subjects with singing talent were no different in their pitch-matching abilities when measured before or after external feedback could be utilized. The untrained subjects with singing talent were also significantly more accurate than the trained singers when external auditory feedback was masked. Both groups were significantly more accurate than the untrained subjects without singing talent.

Adult↗
PubMed1995

Performance feedback increases the incidence of handwashing by staff following patient contact in intensive care.

Nosocomial infections affect up to 30% of ICU patients. Although infection rates decline with increasing handwashing frequency, handwashing rates in ICU's are poor. This study investigated the hypotheses that the subjects' profession would not influence, and performance feedback would not increase, the incidence of handwashing post-patient contact. The study involved an initial period of covert observation to record the baseline level of handwashing, followed by a period of overt observation with regular feedback on handwashing performance by means of letters to staff and histograms of the data displayed in the ICU. Handwashing incidence was reassessed 6 months after performance feedback had ceased. Handwashing differed significantly between professions (P = 0.0001). Initially, the incidence of handwashing was highest amongst wardsmen (90%) and lowest amongst Visiting Medical Officers (VMOs) (20%). Sixty-nine percent (69%) of Registered Nurses (RNs), 57% of physiotherapists, 41% of Resident Medical Officers (RMOs) and 35% of radiographers washed their hands after touching patients. With the exception of the wardsmen, there was a trend towards an increased frequency in handwashing in all groups after performance feedback, but the differences were only statistically significant in the VMO and physiotherapist groups (P < 0.001). The improvements were maintained for 6 months after the feedback phase ended in 4 of the 6 groups.

Critical Care↗
PubMed2003

Internal vs external generation of movements: differential neural pathways involved in bimanual coordination performed in the presence or absence of augmented visual feedback.

It is commonly agreed that a functional dissociation with respect to the internal vs external control of movements exists for several brain regions. This has, however, only been tested in relation to the timing and preparation of motor responses, but not to ongoing movement control. Using functional magnetic resonance imaging (fMRI), the present study addressed the neuroanatomical substrate of the internal-external control hypothesis by comparing regional brain activation for cyclical bimanual movements performed in the presence or absence of augmented visual feedback. Subjects performed a bimanual movement pattern, either with the help of on-line visual feedback of the movements (externally guided coordination) or with the eyes closed on the basis of an internal representation of the movement pattern (internally generated coordination). Visual control and baseline rest conditions were also added. Results showed a clear functional dissociation within the network involved in movement coordination. The hMT/V5+, the superior parietal cortex, the premotor cortex, the thalamus, and cerebellar lobule VI showed higher activation levels when movements were guided by visual feedback. Conversely, the basal ganglia, the supplementary motor area, cingulate motor cortex, the inferior parietal, frontal operculum, and cerebellar lobule IV-V/dentate nucleus showed higher involvement when movements were internally generated. Consequently, the present findings suggest the existence of distinct cortico-cortical and subcortico-cortical neural pathways for externally (augmented feedback) and internally guided cyclical bimanual movements. This provides a neurophysiological account for the beneficial effect of providing augmented visual feedback to optimize movements in normal and motor disordered patients.

Adult↗
PubMed1999

Tactile feedback is present during minimally invasive surgery.

BACKGROUND: The applications of minimally invasive surgery (MIS) and laparoscopy are rapidly expanding. Despite this expansion, our understanding of the importance of haptic feedback during laparoscopic surgery is incomplete. Although many surgeons believe that the use of minimally invasive techniques eliminates force feedback and tactile sensation (haptics), the importance of haptics in MIS has not been fully evaluated. There is considerable interest in the development of simulators for MIS even though the importance of force feedback remains poorly understood. This study was designed to determine the ability of experienced surgeons to interpret haptic feedback with respect to texture, shape, and consistency of an object. STUDY DESIGN: A randomized, single-blinded study was designed. Twenty surgeons were presented objects in a random order, with participants blinded as to their identity. Inspection by direct palpation, conventional instruments, and laparoscopic instruments was performed on all objects. Statistic analysis of the data was performed using chi-square analysis and, when appropriate, a Fischer exact probability test. RESULTS: Direct palpation was associated with the highest accuracy for shape identification and was superior to both conventional instruments (p < 0.001) and laparoscopic instruments (p<0.001). Fine texture analysis with either a conventional instrument or a laparoscopic instrument was superior to direct palpation (p < 0.05). Finally, the three methods of analysis were comparable for consistency analysis. CONCLUSIONS: These data indicate that laparoscopic instruments do, in fact, provide surgeons with haptic feedback. Interpretation of the texture, shape, and consistency of objects can be performed. In some situations, laparoscopic instruments appear to amplify the haptic information available. Our ongoing work is directed at further defining force interactions.

Adult↗
PubMed2005

Closing the loop: follow-up and feedback in a patient safety program.

BACKGROUND: As health care organizations establish patient safety agendas, attention has focused on creating less cumbersome systems for reporting errors. However, experience at Brigham and Women's Hospital (Boston) suggests that more emphasis needs to be placed on what happens after a report is submitted. FOLLOW-UP AND FEEDBACK: Follow-up includes prioritizing opportunities and actions, assigning responsibility and accountability, and implementing the action plan. Feedback entails (1) follow-up to those who report issues and (2) communication to the hospital staff and clinicians about events and actions taken. Responsibility and accountability for improvements need to be assigned by senior administration to hospital leaders who can effect the needed changes. Hospital leaders, not just the members of the patient safety team, must own these changes or improvements. Events that require follow-up action are brought to the attention of risk management and the patient safety team through several mechanisms, including voluntary reporting of adverse events through a computerized safety reporting system, root cause analyses, and Patient Safety Leadership WalkRounds. DISCUSSION: Developing and maintaining a systematic method for feedback represents more of a challenge than the completion of any single recommended action item. However, it is the feedback to the reporter that perpetuates the influx of information and closes the loop. Developing the information-tracking database has made providing feedback easier and more reliable but significant effort is required to keep the database current.

Boston↗
PubMed2001

Changes in hemodynamic response to mental stress with heart rate feedback training.

This study was designed to examine underlying hemodynamic changes that accompany observed reductions in heart rate (HR) response to mental stress following HR feedback training. Twenty-five college males, assigned to either a HR feedback training group (FB+) or a control group (FB-), were presented with a videogame and mental arithmetic challenge, as HR, blood pressure, and impedance cardiography-derived measures of hemodynamic functioning were recorded. During training, the FB+ group received HR feedback and the FB- group was not provided with HR feedback while playing a videogame. At posttraining, results revealed that the FB+ group exhibited significantly lower HR, systolic blood pressure, stroke volume, and total peripheral resistance responses to the videogame compared to that at pretraining. There was no evidence that the acquired skills generalized to a mental arithmetic task. These results suggest that HR feedback training is an effective method for reducing cardiovascular and hemodynamic responses to a mental stressor; however, the generalizability of this effect remains questionable.

Adolescent↗
PubMed2002

EEG signature and phenomenology of alpha/theta neurofeedback training versus mock feedback.

Alpha/theta (a/t) neurofeedback training has in the past successfully been used as a complementary therapeutic relaxation technique in the treatment of alcoholism. In spite of positive clinical outcomes, doubts have been cast on the protocol's specificity when compared to alternative relaxation regimes. This study investigated the basic tenet underlying the a/t training rationale, that accurate a/t feedback representation facilitates the generation of these frequency components. Two groups of healthy volunteers were randomly assigned to either (a) real contingent a/t feedback training or (b) a noncontingent mock feedback control condition. The groups were compared on measures of theta/alpha (t/a) ratios within and across training sessions, as well as activational self-report scales after each session. The contingent a/t feedback group displayed significant within-session t/a ratio increments not evident in the mock control group, as well as higher overall t/a ratios in some but not all of the training sessions. No differences were found between the groups in terms of subjective activational phenomenology, in that both groups reported significantly lower levels of activation after training sessions. The data demonstrate that irrespective of considerations of clinical relevance, accurate a/t neurofeedback effectively facilitates production of higher within-session t/a ratios than do noncontingent feedback relaxation.

Adult↗
PubMed1998

Effect of optical temperature feedback control on patency in laser-soldered microvascular anastomosis.

Feedback control has been postulated to improve the efficacy of laser welding in microsurgery, but alteration of outcome has not been clearly shown. The authors evaluated the ability of an optical closed loop temperature feedback control to improve patency, aneurysm rate, and to histologically limit thermal damage. Rat femoral artery anastomoses were performed under operating microscope magnification. One hundred and twenty-four anastomoses were performed in five groups using 1) free-hand (FH) 1.9-microm laser soldering without feedback; 2) temperature controlled (TC) 1.9-microm laser soldering with optical feedback; 3) FH 808 nm laser; 4) TC 808 nm laser soldering; and 5) 10-0 nylon suture control. In Groups 2 and 4, an optical feedback system controlling laser exposure to produce a preset temperature was used. Anastomotic time was significantly less for all laser groups (p < 0.05). Late patency for all 1.9-microm laser anastomoses was almost 0. Temperature controlled 808-nm anastomoses showed no significant difference from sutures in terms of patency (88 percent vs. 96 percent), bursting pressure, and aneurysm rate, while freehand 808-nm anastomoses had a significantly lower patency (71 percent) and more tissue damage (ANOVA, p < 0.05). The authors conclude that temperature control improves outcome in microvascular anastomosis by reducing transmural thermal injury caused by variations in surgeon technique.

Anastomosis, Surgical↗
PubMed1997

Spatiotemporal dynamics in the coherence collapsed regime of semiconductor lasers with optical feedback.

This paper presents a spatiotemporal characterization of the dynamics of a single-mode semiconductor laser with optical feedback. I use the two-dimensional representation of a time-delayed system (where the delay time plays the role of a space variable) to represent the time evolution of the output intensity and the phase delay in the external cavity. For low feedback levels the laser output is generally periodic or quasiperiodic and with the 2D representation I obtain quasiperiodic patterns. For higher feedback levels the coherence collapsed regime arises, and in the 2D patterns the quasiperiodic structures break and "defects" appear. In this regime the patterns present features that resemble those of an extended spatiotemporally chaotic system. The 2D representation allows the recognition of two distinct types of transition to coherence collapse. As the feedback intensity grows the number of defects increases and the patterns become increasingly chaotic. As the delay time increases the number of defects in the patterns do not increase and there is a signature of the previous quasiperiodic structure that remains. The nature of the two transitions is understood by examining the behavior of various chaotic indicators (the field autocorrelation function, the Lyapunov spectrum, the fractal dimension, and the metric entropy) when the feedback intensity and the delay time vary. (c) 1997 American Institute of Physics.

Journal Article↗
PubMed1980

The effects of delayed and displaced visual feedback on motor control.

Developments in television technology have made possible new approaches to the study of the role of visual feedback in motor control. In two experiments using a special videodisc recording and playback system, the effects of delaying for 66 msec a subject's view of his own hand during a target-directed movement was investigated. The observed effects of such visually delayed feedback compared to spatially distorted feedback produced by prisms led to three major conclusions: (a) despite the behavioral similarity (overshooting) induced by the two kinds of altered feedback, the role of each in the visual-motor control loop is different; (b) adaptation to and the after effect of the two kinds of altered feedback are based on different control mechanisms (c) the processing and use of visual information in hand control requires less time than previous experiments have indicated.

Journal Article↗
PubMed1990

Effects on prism adaptation of duration and timing of visual feedback during pointing.

In two experiments, we investigated the effects of duration of visual feedback of the pointing limb and the time (early to late) in the movement when the limb first becomes visible (timing of visual feedback). Timing, rather than duration of visual feedback, proved to have the greater effect on the relative magnitude of visual and proprioceptive adaptation. Visual adaptation increased smoothly with feedback delay, but corresponding decreases in proprioceptive adaptation underwent an additional sharp change when feedback was delayed until about three-fourths of the way to the terminal limb position. These results are consistent with the idea that visual and proprioceptive adaptation are mediated by exclusive processes. Change in the limb position sense (i.e., proprioceptive adaptation) may be produced by visual guidance of the pointing limb, and view of the limb early in the pointing movement seems to be critical for such visual guidance. The limb may be ballistically released as it nears the terminal position, and, thereafter, any opportunity for visual guidance (i.e., view of the limb) is not effective. On the other hand, change in the eye position sense (i.e., visual adaptation) may be mediated by proprioceptive guidance of the eye; the eyes may track the imaged position of the nonvisible limb. Such proprioceptive guidance seems to be solely a function of the distance moved before the limb becomes visible.

Journal Article↗
PubMed1992

Effects of Pointing Rate and Availability of Visual Feedback on Visual and Proprioceptive Components of Prism Adaptation.

While looking through laterally displacing prisms, subjects pointed 60 times straight ahead of their nose at a rate of one complete movement every 2 or 3 s, with visual feedback available early in the pointing movement or delayed until the end of the movement. Sagittal pointing was paced such that movement speed covaried with pointing rate. Aftereffect measures (obtained after every 10 pointing trials) showed that when the limb became visible early in a pointing movement, proprioceptive adaptation was greater than visual, but when visual feedback was delayed until the end of the movement, the reverse was true. This effect occurred only with the 3-s pointing rate, however. With the 2-s pointing rate, adaptation was predominately proprioceptive in nature, regardless of feedback availability. Independent of the availability of visual feedback, visual adaptation developed more quickly with 3-s pointing, whereas proprioceptive adaptation developed more rapidly with 2-s pointing. These results are discussed in terms of a model of perceptual-motor organization in which the direction of coordinative (guidance) linkage between eye-head (visual) and hand-head (proprioceptive) systems (and consequently the locus of discordance registration and adaptive recalibration) is determined jointly by pointing rate and feedback availability. An additional effect of pointing rate is to determine the rate of discordant inputs. Maximal adaptive recalibration occurs when the input (pointing) rate matches the time constant of the adaptive encoder in the guided system.

Journal Article↗
PubMed1994

Effects of movement duration and visual feedback on visual and proprioceptive components of prism adaptation.

While looking through laterally displacing prisms, subjects pointed sagittally 80 times at an objectively straight-ahead target, completing a reciprocal out-and-back pointing movement ever 1, 3, or 6 s. Visual feedback was available early in the pointing movement or only late at the end of the movement. Aftereffect measures of adaptive shift (obtained after every 10 pointing trials) showed adaptive change only in limb position sense (i.e., proprioceptive adaptation) when movement duration was 1 s, regardless of visual feedback condition; but as movement duration increased, adaptive change in the eye position sense (i.e., visual adaptation) increased while proprioceptive adaptation decreased, especially for the late visual feedback condition. Regardless of visual feedback condition, proprioceptive adaptation showed the maximal rate of growth with the 1-s movement duration, whereas visual adaptation showed maximal growth with the 6-s movement duration. These results provide additional support for a model of adaptive spatial mapping in which the direction of strategically flexible coordination (guidance) between eye and limb (and consequently the locus of adaptive spatial mapping) is jointly determined by movement duration and timing of visual feedback. An additional effect of movement duration is to determine the rate of discordant inputs. Maximal growth of adaptation occurs when the input rate matches the response time of the spatial mapping function.

Journal Article↗