Artificial Delay Research Articles

Neural Correlates of State Estimation in Visually Guided Movements: an Event-Related FMRI Study

State estimation of self-movement, based on both motor commands and sensory feedback, has been suggested as essential to human movement control to compensate for inherent feedback delays in sensorimotor loops. The present study investigated the neural basis for state estimation of human movement using event-related functional magnetic resonance imaging (fMRI). Participants traced visually presented curves with a computer mouse, and an artificial delay was introduced to visual feedback. Motor performance and brain activities during movements were measured. Experiment 1 investigated brain activations that were significantly correlated with visual feedback delay and motor error by parametrically manipulating visual feedback delay. Activation of the right posterior parietal cortex (PPC) was positively correlated with motor error, whereas activation of the right temporo-parietal junction (TPJ) was observed only in the group with a smaller increase in motor error with increased visual feedback delay. Experiment 2 involved parametric analysis of motor performance while controlling mouse movement speed during the task. Activity in the right TPJ showed a significant positive correlation with motor performance under the delayed visual feedback condition. In addition, activity of the PPC was greater when motor error was presented visually. These results suggest that the PPC plays a significant role in evaluating visuomotor prediction error, while the TPJ is involved in state estimation of self-movement during visually guided movements.

Comparison of fuzzy logic and artificial neural networks approaches in vehicle delay modeling

Modeling vehicle delay has been an interesting subject for traffic engineers and urban planners. Determination of vehicle delay is a complex task and the delay is influenced by many variables that have uncertainties and vagueness, especially for non-uniform or over-saturated conditions. In this study, vehicle delay is modeled using new approaches such as Fuzzy Logic (FL) and Artificial Neural Networks (ANN) to deal with all conditions. The Neuro Fuzzy Delay Estimation (NFDE) model and Artificial Neural Networks Delay Estimation (ANNDE) model are developed. The overall delay data required for the model were collected from ten signalized intersections in Turkey. The results of the developed models are compared with the Highway Capacity Manual (HCM), Akçelik’s methods and the delay data collected from intersections. The results showed that delay estimations by the ANNDE and NFDE model are promising. It is also inferred that the NFDE model results are the best fitted. The Average Relative Error (ARE) rates of NFDE model are determined as 7% for under-saturated and 5% for over-saturated conditions. The results reflect the fact that the neuro-fuzzy approach may be used as a promising method in vehicle delay estimation.

Unbiased adaptive feedback cancellation in hearing aids by closed-loop identification

Hearing aid users often suffer from feedback which causes "howling" and limits the maximum stable gain. The direct method of adaptive feedback cancellation is widely used to mitigate feedback, however it is less effective for high forward path gains due to the inherent bias in the feedback path estimate. This bias can be reduced at the expense of artificial delays which can potentially introduce pre-echo and "comb filter" effects. The direct method also tends to cancel tonal audio signals such as alarms and music. We propose using a system identification method in closed-loop for unbiased feedback cancellation which does not possess the negative characteristics manifested by the direct method, but uses an identification signal. The two-stage method which employs two adaptive filters, one to identify the entire closed-loop, and another to extract the feedback path response was the preferred unbiased method due to its low computation and good feedback identification particularly during "howling." This paper presents the theory of the proposed new method, and computer simulations which demonstrate its advantages over the widely used direct method.

Low molecular weight species of tau in Alzheimer's disease are dependent on tau phosphorylation sites but not on delayed post-mortem delay in tissue processing

Gel electrophoresis and Western blotting of sarkosyl-insoluble fractions enriched in hyper-phosphorylated tau in Alzheimer disease (AD) have been used to analyze the pattern of phospho-tau by using different antibodies directed to the amino-terminal, core and carboxyl terminus of tau, and by using samples with increased artificial post-mortem delay in order to gain understanding on the characteristics of the band pattern and its vulnerability to post-mortem degradation. In addition to the typical profile of three major bands of 68, 64 and 60 kDa, several bands of lower molecular weight have been distinguished in frontal cortex homogenates in four AD cases stage V of Braak and Braak in optimal samples with 2 h of post-mortem delay. Lower bands, ranging from 60 to 22 kDa, are best seen with antibodies directed to the core of tau protein and, particularly, to the carboxy-terminus, thus suggesting the presence of truncated or cleaved forms of tau containing the C-terminal region. This pattern is not the result of post-mortem degradation, as artificial post-mortem delay of the same sample does not reveal the appearance of new bands with time. On the contrary, tau degradation, manifested as a reduction in the number and intensity of the bands, may occur between 8 and 26 h post-mortem and is universal in samples with post-mortem delays of 50 h.

Passive depolariser based on artificial polarisation-dependent delay

A passive depolariser based on artificial polarisation-dependent delay is demonstrated. Experimental results show that a low degree of polarisation (<2%) and a low polarisation-dependent loss (0.08 dB) are obtained for any input state of polarisation.

Metamodel-Driven Design Optimization Using Integrative Graphical Design Interfaces: Results From a Job-Shop Manufacturing Simulation Experiment

Today, engineers are relying more on modern computer tools and techniques to visualize complex data sets; however, few studies have examined the effect of fast, graphical design interfaces on user performance during system design. The objective in this paper is to extend our previous findings in this area by examining the impact of fast, graphical design interfaces on design efficiency and design effectiveness within the context of a job-shop design problem. We accomplish this by investigating the effect of an artificial response delay, intended to mimic computationally intensive analyses, on user performance. Experimental results indicate that user performance deteriorates significantly when a small response delay of 1.5 s is introduced: percent error and task completion time increase, on average, by 9.4% and 81 s, respectively, when the delay is present. The use of first-order, stepwise, and second-order polynomial regression models for approximating the system responses (outputs) is also investigated, and user performance is found to improve when stepwise polynomial regression models are used instead of first- or second-order models. The stepwise models yielded 12% lower error and 91 s faster completion times, on average, over the first-order models; error was 13.5% lower and completion time was 62 s faster, on average, than when second-order models were used. The results confirm our previous findings about the negative impact of response delay on task completion time while demonstrating that delay can also significantly decrease the efficacy of a metamodel-driven graphical design interface.

Multiple-electrode nerve cuffs for low-velocity and velocity-selective neural recording

In the paper, a method using multiple-electrode nerve cuffs is presented that enables electroneurographic signals (ENG) to be recorded selectively by action potential velocity. The theory uses a one-dimensional model of the electrodes in the cuff. Using this model, the transfer function for a single tripole is derived, and it is shown that more than one tripole signal can be recorded from within a cuff. When many tripole signals are available and are temporally aligned by artificial delays and summed, there is a significant increase in the amplitude of the recorded action potential, depending on the cuff length and the action potential velocity, with the greatest gain occurring for low velocities. For example, a cuff was considered that was constrained by surgical considerations to 30 mm between the end electrodes. For action potentials with a velocity of 120 m s(-1), it was shown that, as the number of tripoles increased from one, the peak energy spectral density of the recorded output increased by a factor of about 1.6 with three tripoles, whereas, for 20 m s(-1), the increase was about 19, with ten tripoles. The time delays and summation act as a velocity-selective filter. With consideration of the energy spectral densities at frequencies where these are maximum (to give the best signal-to-noise ratio), the tuning curves are presented for these velocity-selective filters and show that useful velocity resolution is possible using this method. For a 30 mm cuff with nine tripoles, it is demonstrated that it is possible to resolve at least five distinct velocity bands in the range 20-120m s(-1).

Experimental and computational analysis of monkey smooth pursuit eye movements.

Smooth pursuit eye movements are guided by visual feedback and are surprisingly accurate despite the time delay between visual input and motor output. Previous models have reproduced the accuracy of pursuit either by using elaborate visual signals or by adding sources of motor feedback. Our goal was to constrain what types of signals drive pursuit by obtaining data that would discriminate between these two modeling approaches, represented by the "image motion model" and the "tachometer feedback" model. Our first set of experiments probed the visual properties of pursuit with brief square-pulse and sine-wave perturbations of target velocity. Responses to pulse perturbations increased almost linearly with pulse amplitude, while responses to sine wave perturbations showed strong saturation with increasing stimulus amplitude. The response to sine wave perturbations was strongly dependent on the baseline image velocity at the time of the perturbation. Responses were much smaller if baseline image velocity was naturally large, or was artificially increased by superimposing sine waves on pulse perturbations. The image motion model, but not the tachometer feedback model, could reproduce these features of pursuit. We used a revision of the image motion model that was, like the original, sensitive to both image velocity and image acceleration. Due to a saturating nonlinearity, the sensitivity to image acceleration declined with increasing image velocity. Inclusion of this nonlinearity was motivated by our experimental results, was critical in accounting for the responses to perturbations, and provided an explanation for the unexpected stability of pursuit in the presence of perturbations near the resonant frequency. As an emergent property, the revised image motion model was able to reproduce the frequency and damping of oscillations recorded during artificial feedback delays. Our second set of experiments replicated prior recordings of pursuit responses to multiple-cycle sine wave perturbations, presented over a range of frequencies. The image motion model was able to reproduce the responses to sine wave perturbations across all frequencies, while the tachometer feedback model failed at high frequencies. These failures resulted from the absence of image acceleration signals in the tachometer model. We conclude that visual signals related to image acceleration are important in driving pursuit eye movements and that the nonlinearity of these signals provides stability. Smooth pursuit thus illustrates that a plausible neural strategy for combating natural delays in sensory feedback is to employ information about the derivative of the sensory input.

A load torque compensation scheme under the speed measurement delay

The average speed detection method involves a measurement delay, which can cause a serious instability problem to the unknown load torque observer. The instability can be cured by inserting an artificial delay into the torque-filtering path of the observer. Also, by utilizing the concept of the phase lead compensator, we propose a method of designing an arbitrary high-order low-pass filter (Q filter). Through the results of simulation and experiments, we show that our proposed method yields more robust and improved results than the conventional load torque observer.

Efficient multiwavelength dynamic model for erbium-doped fiber amplifier

An efficient full spectrum (1480-1600 nm) large-signal transient dynamic model of an erbium-doped fiber amplifier (EDFA) is developed. A technique to speed up the simulation by a factor of 1000 using artificial delay lines based on the transmission-line model (TLM) is presented. Simulations and experimental results show the delay line method is not detrimental to the accuracy of the model. The efficiency of this model means it is ideal for simulating the dynamics of large wavelength division multiplexed (WDM) networks if included in a network simulator.

Acousto-fluidic sound augmentation for Orthodox Jewish worship spaces

An acousto-fluidic sound augmentation system has been developed which provides adequate sound coverage in worship spaces accommodating as many as 1600 persons. Because of the unique religious restrictions of Orthodox Judaism, use of electricity and sound reproduction per se are prohibited while sound augmentation is permissible as long as the original sound is preserved and no apparent sound amplification occurs. A kosher sound system has been built and tested with essentially 0-dB sound-level gain but about 50 dB of power gain when operating with a 10-psi air source. The system frequency response is flat from 700–3500 Hz, and cuts off at 200 and 6000 Hz, respectively. A single-channel output comprises two 180° out-of-phase ElectroVoice HB640 horns. The monaural sound quality is good enough for recognition of the speaker’s voice with good reproduction of sufficient overtones to render singing pleasant. Sounds can be transmitted up to 25 m through 5-cm-diam PVC pipes thereby allowing speakers to be placed far enough away from the inputs to ensure good aural reception at the furthest reaches of worship spaces. The inherent acoustic delay obviates the need for the introduction of artificial delays and consequently results in very natural sound propagation and rendition.

On the outage probability in local/regional single frequency broadcasting networks

A receiver in an ODFM based broadcasting system allows all transmitters in a radio network to simultaneously broadcast the same information in the same frequency block. This procedure generates an artificial multipath environment at the receiver. Since the receiver is designed to overcome these problems, such a Single Frequency Network (SFN) provides good coverage and frequency economy in national applications. However, the efficiency in local SFN has been questioned. The network planning of local SFNs is a mixture of conventional frequency reuse planning and planning to avoid excessive propagation delays caused by the artificial delay spread. In this paper we propose some rules of thumb to be considered in the design of local SFNs. The coverage properties in SFNs are strongly dependent on the transmitter density which determines the degree of diversity of receiving signals from several transmitters. Results indicate that required coverage can be attained in local networks using three OFDM frequency blocks, provided that seven transmitters are used to cover each regional service area. The results also indicate that the duration of the guard interval between two consecutive OFDM signals has to be chosen with some care dependent on the size of the service area. Furthermore, we show that there exists an optimal antenna height for a given coverage area and guard interval.

EFFECT OF ETHEPHON ON BLOOM DELAY IN ALMOND TREES.

Under temperate climates almond production is restricted to areas without risk of frosts on flowering. However an artificial delay of flowering would be beneficial to avoid frost damages under such conditions. With the objetive of delay flowering, foliar applications of Ethephon were made to mature almond trees in the fall 1990 and 1991, when their natural defoliation was 10%. Three rates of Ethephon and a check were evaluated for that proposal. Bloom delay was 7, 8 and 9 days for 75, 150 and 300 mg·L-1 in the first year the three rates decreased fruit set and fruit yield. In the second year of evaluation the bloom was delayed only 3 days at the highest rate but fruit set and fruit yield was not affected. In both years fruit quality was the same for all the treatment.

Oculo-manual coordination control: ocular and manual tracking of visual targets with delayed visual feedback of the hand motion.

The aim of this study was to examine coordination control in eye and hand tracking of visual targets. We studied eye tracking of a self-moved target, and simultaneous eye and hand tracking of an external visual target moving horizontally on a screen. Predictive features of eye-hand coordination control were studied by introducing a delay (0 to 450 ms) between the Subject's (S's) hand motion and the motion of the hand-driven target on the screen. In self-moved target tracking with artificial delay, the eyes started to move in response to arm movement while the visual target was still motionless, that is before any retinal slip had been produced. The signal likely to trigger smooth pursuit in that condition must be derived from non-visual information. Candidates are efference copy and afferent signals from arm motion. When tracking an external target with the eyes and the hand, in a condition where a delay was introduced in the visual feedback loop of the hand, the Ss anticipated with the arm the movement of the target in order to compensate the delay. After a short tracking period, Ss were able to track with a low lag, or eventually to create a lead between the hand and the target. This was observed if the delay was less than 250-300 ms. For larger delays, the hand lagged the target by 250-300 ms. Ss did not completely compensate the delay and did not, on the average, correct for sudden changes in movement of the target (at the direction reversal of the trajectory). Conversely, in the whole range of studied delays (0-450 ms), the eyes were always in phase with the visual target (except during the first part of the first cycle of the movement, as seen previously). These findings are discussed in relation to a scheme in which both predictive (dynamic nature of the motion) and coordination (eye and hand movement system interactive signals) controls are included.

IMPROVING CONTROL PERFORMANCE OF MULTIVARIABLE SYSTEMS BY MODIFICATION OF THE PROCESS DEADTIME STRUCTURE

A new multivariate deadtime control algorithm was designed in a previous paper. This algorithm, while very efficient, was developed under the restriction that the deadtimes on the diagonal of the transfer function matrix are less than the others in each row. In this paper, we further investigate this restriction's effect on the performance of the control system, and show that this restriction can be achieved by rearranging the order of the input variables and adding artificial delays. Several examples demonstrate the significance of the results.

Effect of artificial voice feedback delay in typing and its implications for the blind user

We examined the effect of voice-feedback delay on learning to type nonsense strings on a reduced computer terminal keyboard. The results suggest that long delays (1,642 msec) affect learning of the keyboard before mastery, whereas shorter delays (841 msec) do not. With mastery, subjects learn to ignore the disruptive effects of long feedback delays. Feedback delay may nevertheless be an important human-factors issue for blind consumers who are learning to type with a voice-based system, and for hardware and software designers of systems for the blind and visually impaired.

Windowless position-sensitive x-ray detector for a Rowland circle crystal spectrometer

The output from an x-ray detector using a Chevron pair of microchannel plates has been linearly encoded using an artificial delay line technique. The detector, operating in the wavelength region 12–30 Å, has been mounted on the focusing plane of a Johann crystal spectrometer, radius 25 cm, and used to survey the spectrum from the Divertor Injection Tokamak Experiment (DITE) tokamak. The 20×20 mm2 detector is encoded by a remote, CAMAC based, computer acquisition system which at an electronic count rate of 1×105 Hz shows negligible degradation of the spectral profiles. Events encoded along the 20-mm dimension are directly histogrammed into a CAMAC memory which is capable of recording 128 time frames each with 256 spectral bins with 12 bits/bin. In nonoptimized tests, a FWHM of 60 μm is observed, and a count rate up to 2×104 Hz/mm has been achieved. The high-resolution capability and the shallow detection depth of the microchannel plate both complement the low f number of the spectrometer. Results are reported for the DITE tokamak.

Improving the performance of the MWPC X-ray imaging detector by means of the multi-step avalanche technique

X-ray imaging systems based on conventional MWPC technology and artificial delay line readout techniques have been developed at RAL for several applications over a period of some eight years. Successful as this effort has been, it is now perceived that very limited scope exists for the further improvement of the imaging capability of the standard MWPC design. Attention has therefore been turned to the possibility of exploiting the multi-step avalanche (MSA) system of electron multiplication in this context. Results from a prototype system are presented which show spatial resolution better than that achieved in our MWPC systems with no wire artefacts in the image. The facility for controlling the effective depth of the detector electronically is also demonstrated so offering some alleviation of the parallax problem common to all gaseous X-ray detectors.

Fault-tolerant broadcast of routing information

An algorithm is presented for the reliable broadcast of routing information throughout a network. The algorithm anticipates the possibility of long-delayed packets, line and node outages, network partitions, hardware failures, and a history of arbitrarily corrupted databases throughout the network. After any failure, the algorithm stabilizes in reasonable time without human intervention, once any malfunctioning equipment is repaired or disconnected. The algorithm also has the advantages of not requiring frequent control traffic in the absence of topological changes, not imposing artificial delays on nodes upon startup, and not relying on timers in ordinary operation. The algorithm is compared to a functionally similar algorithm in the ARPANET.

A new implementation algorithm of second-order IIR digital filters

In the implementation of a second-order IIR digital filter, five multiplications and four additions are required for each output sample calculation. In this correspondence we present a new implementation algorithm which requires four multiplications and seven additions per output sample, and the output sequence can be produced at uniform rate without introducing any artificial delay in the filter. Since the number of operations (such as multiplication, addition, data transfer, etc.) between any two consecutive input samples are kept the same, the design of the control section is quite simple. For the circumstances where multiplication time dictates the filter speed, the new algorithm achieves 20 percent improvement on the filter speed.