Time Delays In Feedback Research Articles

Time delays, competitive interdependence, and firm performance

Research summary: Competitors' experiences of prior interactions shape patterns of rivalry over time. However, mechanisms that influence learning from competitive experience remain largely unexamined. We develop a computational model of dyadic rivalry to examine how time delays in competitors' feedback influence their learning. Time delays are inevitable because the process of executing competitive moves takes time, and the market's responses unfold gradually. We analyze how these lags impact learning and, subsequently, firms' competitive behavior, industry profits, and performance heterogeneity. In line with the extant learning literature, our findings reveal that time delays hinder learning from experience. However, this counterintuitively increases rivals' profits by reducing their investments in costly head‐to‐head competition. Time delays also engender performance heterogeneity by causing rivals' paths of competitive behavior to diverge.Managerial summary: While competitive actions such as new product launches, geographical expansion, and marketing campaigns require up‐front resource commitments, the potential lift in profits takes time to materialize. This time delay, combined with uncertainty surrounding the outcomes of competitive actions, makes it difficult for managers to learn reliably from previous investment decisions. This results in systematic underinvestment in competitive actions. The severity of the underinvestment grows as the time delay between an investment and its positive results increases. Counterintuitively, however, competitors' collective underinvestment increases profit‐making opportunities. In industries with large time delays, companies that do invest in competitive actions are likely to enjoy high returns on investment. It is also likely that rivals' paths of competitive behavior bifurcate. Together, these mechanisms generate large differences in competitors' profits. Copyright © 2016 John Wiley & Sons, Ltd.

Modeling the Male Reproductive Endocrine Axis: Potential Role for a Delay Mechanism in the Inhibitory Action of Gonadal Steroids on GnRH Pulse Frequency.

We developed a compartmental model so we could test mechanistic concepts in the control of the male reproductive endocrine axis. Using SAAM II computer software and a bank of experimental data from male sheep, we began by modeling GnRH-LH feed-forward and LH-T feedback. A key assumption was that the primary control signal comes from a hypothetical neural network (the PULSAR) that emits a digital (pulsatile) signal of variable frequency that drives GnRH secretion in square wave-like pulses. This model produced endocrine profiles that matched experimental observations for the testis-intact animal and for changes in GnRH pulse frequency after castration and T replacement. In the second stage of the model development, we introduced a delay in the negative feedback caused by the aromatization of T to estradiol at the brain level, a concept supported by empirical observations. The simulations showed how changes in the process of aromatization could affect the response of the pulsatile signal to inhibition by steroid feedback. The sensitivity of the PULSAR to estradiol was a critical factor, but the most striking observation was the effect of time delays. With longer delays, there was a reduction in the rate of aromatization and therefore a decrease in local estradiol concentrations, and the outcome was multiple-pulse events in the secretion of GnRH/LH, reflecting experimental observations. In conclusion, our model successfully emulates the GnRH-LH-T-GnRH loop, accommodates a pivotal role for central aromatization in negative feedback, and suggests that time delays in negative feedback are an important aspect of the control of GnRH pulse frequency.

Similarity of finger and hand intermittent corrective movements

Event Abstract Back to Event Similarity of finger and hand intermittent corrective movements Jason Friedman1, 2* and Lior Noy3, 4 1 Tel Aviv University, Physical Therapy, Israel 2 Tel Aviv University, Sagol School of Neuroscience, Israel 3 Weizmann Institute of Science, Molecular Cell Biology, Israel 4 Weizmann Institute of Science, The Theatre Lab, Israel Due to the inherent time delays in processing visual and proprioceptive feedback, it is believed that the central nervous system uses intermittent control as a way of producing stable movement, that is, corrections are made at discrete points in time rather than continuously. While several lines of evidence support this notion, the nature of this corrective process is largely unknown. In this study, we examined whether intermittent control results mostly from a central process by comparing two motor tasks with vastly different inertial properties and determining whether the frequency of these corrections is similar. We examined the frequency of these corrections when subjects attempted to move synchronously with (i.e. imitate) the motion of an unpredictably oscillating stimulus, with varying frequency and amplitude. Subjects performed the same task with two different types of movement - either raising and lowering the index finger, or moving a pen backwards and forwards, with the movements recorded with a motion capture system. We defined the onset of a corrective movement as a zero-crossing in the filtered acceleration profile, and removed the acceleration zero-crossings which corresponded to acceleration zero-crossings in the stimuli. We summarized for each subject the frequency of corrections using the value corresponding to the peak of the frequency histogram. We found that while the frequency of these corrections varied significantly across subjects (0.7 - 1.1 Hz), a similar frequency was used by each subject for the two tasks. These results support the notion that corrective movements results from a central process, and it is likely that a similar process is used for the two different movement types. Further, the significant between-subject variation suggests that the timing of these corrective movements varies across individuals, which is likely to affect strategies used for movement generation. Keywords: Hand, Movement, Imitation, motor control, Intermittent control, Finger Conference: XII International Conference on Cognitive Neuroscience (ICON-XII), Brisbane, Queensland, Australia, 27 Jul - 31 Jul, 2014. Presentation Type: Poster Topic: Motor Behaviour Citation: Friedman J and Noy L (2015). Similarity of finger and hand intermittent corrective movements. Conference Abstract: XII International Conference on Cognitive Neuroscience (ICON-XII). doi: 10.3389/conf.fnhum.2015.217.00167 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 19 Feb 2015; Published Online: 24 Apr 2015. * Correspondence: Dr. Jason Friedman, Tel Aviv University, Physical Therapy, Tel Aviv, Israel, jason@tau.ac.il Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Jason Friedman Lior Noy Google Jason Friedman Lior Noy Google Scholar Jason Friedman Lior Noy PubMed Jason Friedman Lior Noy Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Maintenance of the Upright Posture in Humans upon Manipulating the Direction and Delay of Visual Feedback

We examined the maintenance of the upright posture in subjects immersed in a 3D virtual visual environment, VVE. The latter consisted of two plans; the VVE foreground represented the image of a room window, while the background looked like an outside urban landscape. The position of the foreground (window) was linked, using the respective software, with body sways in the sagittal plane and shifted in accordance with body movements, while the background always remained immobile. By manipulating the direction and time delay of the relationship between the body sways and shifts of the VVE foreground, we tried to estimate the contribution of visual signals to postural control. For this purpose, we used the technique of frequency filtration of displacements of the center of feet pressure (CFP) and, in such a way, detected signals proportional to movements of the general center of gravity (CG) of the body (CG variable). After this, we calculated the difference between the CFP and CG shifts (CFP-CG-variable). The latter variable is known to be proportional to the horizontal acceleration; this is why it was used for estimation of the muscular torques correcting CG shifts. Analysis of changes in the above variables (CG and CFP-CG) demonstrated a clear dependence between the root mean square (RMS) of their amplitude spectra on the direction of feedback between body sways and shifts of the VVE foreground. With a synphase (SPh) pattern of the link between shifts of the body and those of the VVE foreground, the RMS values were closer to the range typical of standing with the eyes closed, while with an antiphase (APh) link, they were closer to the zone of values observed under conditions of normal vision. Introduction of time delays in feedback between sagittal body sways and shifts of the VVE foreground exerted nearly similar effects on the CG and CFP-CG variables. In both SPh and APh relations, 0.2- and 0.5-sec-long time delays resulted in increases in the RMS of the sway spectrum, while 0.8- and 1.0-sec-long delays led to RMS decreases. Thus, our findings show that the maintenance of upright stance under conditions of manipulations of the direction and time delay of visual feedback is performed, at least partly, with the use of an unstable VVE foreground as the reference. This can be considered proof of a special (frequently, dominating) role of the visual signals in postural control.

Asymptotic stability in a flexible-joint robot with model uncertainty and multiple time delays in feedback

This study considers the stability problem of a flexible-joint robot in case time delays are involved in the feedback loop. We assume in our analysis that the controller uses only position measurements. The single and multiple time-delay cases, are considered. By using some useful structural properties of the robot model, sufficient conditions for asymptotic (exponential) stability of the system under consideration have been established. An estimate to the system rate of convergence is given and a procedure for evaluating the region of attraction, is given.

DELAY-INDEPENDENT STABILITY OF RETARDED DYNAMIC SYSTEMS OF MULTIPLE DEGREES OF FREEDOM

On the basis of generalized Sturm theory, this paper presents a simple, but systematic approach to the delay-independent stability analysis of the linear dynamic systems involving multiple degrees of freedom and possibly two time delays. The approach enables one to complete the stability analysis in a much simpler way than before through the use of a MAPLE routine given in the paper. To demonstrate the approach, the paper gives a detailed analysis, the corresponding sufficient and necessary conditions as well as stable regions in parameter space of concern for the delay-independent stability of a vibrating system with time delays in state feedback, an active-tendon for a tall structure and an active suspension of a quarter car model.

Delayed responses and stability in two-species systems

AbstractIt is shown that if intraspecific self-regulating negative feedback effects are strong enough such that a nontrivial steady state of a two species system is locally asymptotically stable, then time delays in the positive feedback as well as in other interspecific interactions cannot destabilise the system and hence delay induced instability leading to persistent oscillations is impossible whatever the magnitude of the time delays. A method is also proposed for an estimate of decay rate of perturbations.

The time relationship of performance and audit feedback on conformance with emergency department process criteria

Adherence to physician-developed process criteria is critical to the medical and legal acceptance of algorithm-directed nonphysician care of acute non-life-threatening illnesses seen in the emergency department. It is generally assumed that adherence to prescribed medical process criteria results in acceptable patient outcomes. We evaluated changes in compliance with varying time delays in audit feedback and varying degrees of supervision. Our evaluation indicated that, under ideal circumstances of daily audit and supervisory feedback, a conformance rate of 80% was achieved. This is a 100% improvement over a group in which neither element was operative.

Reactivity feedback with short delay times

Analytical expressions based on the point reactor model are presented for the increase in peak power, temperature and energy release-caused by short time delays in the temperature feedback of reactivity-in superpromptcritical excursions. A criterion is presented to decide whether the delay time ought to be included in the analysis or not. Two specific cases, slowing-down delay and heat transfer delay of Doppler feedback in Na cooled fast breeder reactors are discussed.