Detecting system failures from durations and binary cues

Durations are often used to judge the status of an invisible process. However, the apparent duration of an interval depends on the actual duration and on other variables, such as the workload during the interval and the person's expectations. An experiment dealt with the use of durations as an information source on the state of an invisible process and the effects of expectations and workload on decisions regarding the process. Eighty-nine participants observed a computerized simulation of a process which could be either intact or faulty, with intact processes ending on average sooner than faulty ones, and they had to indicate whether or not the process is intact and to estimate its duration. A binary cue with either intermediate or no validity indicated whether the process was supposedly intact or not, generating expectations about the duration of the process. Perceived durations and the decisions about the intactness of a process depended on the actual process duration, as well as on the expectations generated by the binary cue. In addition, task workload affected time estimates, but it had no effect on participants' tendency to adhere to cue recommendations or their ability to distinguish between intact and faulty processes. Results show that users' duration-based decisions about the status of a computerized process are affected by internal and external cues. While users can use durations as an information source, they should, whenever possible, be accompanied by additional indicators, lowering the inherent uncertainty in the duration estimation process.     

A computationally efficient frequency-domain LMS algorithm withconstraints on the adaptive filter

The frequency domain implementation of the LMS algorithm is attractive due to both the reduced computational complexity and the potential of faster convergence compared with the time domain implementation. Another advantage is the potential of using frequency-domain constraints on the adaptive filter, such as limiting its magnitude response or limiting the power of its output signal. This paper presents a computationally efficient algorithm that allows the incorporation of various frequency domain constraints into the LMS algorithm. A penalty function formulation is used with a steepest descent search to adapt the filter so that it converges to the new constrained minimum. The formulation of the algorithm is derived first, after which the use of some practical constraints with this algorithm and a simulation example for adaptive blind equalization are described     

Spatial Aliasing in Spherical Microphone Arrays

Performance of microphone arrays at the high-frequency range is typically limited by aliasing, which is a result of the spatial sampling process. This paper presents analysis of aliasing for spherical microphone arrays, which have been recently studied for a range of applications. The paper presents theoretical analysis of spatial aliasing for various sphere sampling configurations, showing how high-order spherical harmonic coefficients are aliased into the lower orders. Spatial antialiasing filters on the sphere are then introduced, and the performance of spatially constrained filters is compared to that of the ideal antialiasing filter. A simulation example shows how the effect of aliasing on the beam pattern can be reduced by the use of the antialiasing filters     

Perception of traffic risks for older and younger adults

The study examined differences in the perception of traffic risks for older and younger adults. Thirty-four younger participants (mean age 24.7 years) and 30 older participants (mean age 70 years) estimated the number of younger and older people (out of 100,000 people) that were injured in car and pedestrian crashes in a recent year. Both age groups viewed older adults’ risks in pedestrian crashes as higher than those of younger adults, and saw older adults’ risks in car crashes as identical to the risks for younger adults. Both age groups assessed the risks for their own group quite accurately, but erred in their assessment of the risk for the other group. Older participants tended to overestimate the risk for younger adults, and younger participants tended to underestimate the risk for older adults. These results point to the need to enhance awareness of the age-related increase in traffic risk, which could potentially promote more considerate driving behavior.     

Frequency-domain adaptation of causal digital filters

The adaptation of causal FIR digital filters in the discrete frequency domain is considered, and it is shown how the bin-normalized form of the LMS algorithm can converge to a biased solution for problems such as linear prediction. A discrete frequency-domain version of Newton's algorithm is derived, and it is demonstrated how this can converge to the optimal causal solution, even for linear prediction problems. The algorithm employs a spectral factorization of the estimated power spectral density of the reference signal, the entirely noncausal part of which is used before the causality constraint in the adaptation algorithm, and the entirely causal part is applied after the causality constraint. The spectral factors can be calculated online from a recursive estimate of the power spectral density without too great a loss of convergence speed. The extension of the algorithm to the adaptation of feedforward controllers is also described, in which case, the spectral factors of the reference signals filtered by the plant response are required, and these are shown to be equal to the spectral factors of the reference signal multiplied by the minimum phase part or the plant frequency response     

The Spherical-Shell Microphone Array

Spherical microphone arrays have been recently studied for a wide range of applications. In particular, microphones arranged around an open or virtual sphere are useful in scanning microphone arrays for sound field analysis. However, open-sphere spherical arrays have been shown to have poor robustness at frequencies related to the zeros of the spherical Bessel functions. This paper presents a framework for the analysis of array robustness using the condition number of a given matrix, and then proposes several robust array configurations. In particular, a dual-sphere configuration previously presented which uses twice as many microphones compared to a single-sphere configuration is analyzed. This paper then shows that high robustness can be achieved without increasing the number of microphones by arranging the microphones in the volume of a spherical shell. Another simpler configuration employs a single sphere and an additional microphone at the sphere center, showing improved robustness at the low-frequency range. Finally, the white-noise gain of the arrays is investigated verifying that improved white-noise gain is associated with lower matrix condition number.