Mean and Random Errors of Visual Roll Rate Perception from Central and Peripheral Visual Displays

A large number of roll rate stimuli, covering rates from zero to plus or minus 25 deg/sec, were presented to subjects in random order at 2 sec intervals. Subjects were to make estimates of magnitude of perceived roll rate stimuli presented on either a central display, on displays in the peripheral ield of vision, or on all displays simultaneously. Response was by way of a digital keyboard device, stimulus exposition times were varied. The present experiment differs from earlier perception tasks by the same authors in that mean rate perception error (and standard deviation) was obtained as a function of rate stimulus magnitude, whereas the earlier experiments only yielded mean absolute error magnitude. Moreover, in the present experiment, all stimulus rates had an equal probability of occurrence, whereas the earlier tests featured a Gaussian stimulus probability density function. Results yield a ood illustration of the nonlinear functions relating rate presented to rate perceived by human observers or operators

Effects of metal-on-metal wear on the host immune system and infection in hip arthroplasty

Methods We reviewed the available literature on the influence of degradation products of MOM bearings in total hip arthroplasties on infection risk. Results Wear products were found to influence the risk of infection by hampering the immune system, by inhibiting or accelerating bacterial growth, and by a possible antibiotic resistance and heavy metal co-selection mechanism. Interpretation Whether or not the combined effects of MOM wear products make MOM bearings less or more prone to infection requires investigation in the near future

Entrepreneurial orientation and the business performance of SMEs: a quantitative study from the Netherlands

Entrepreneurial Orientation (EO) is often mentioned as an antecedent of growth, competitive advantage and superior performance, and prior empirical research has often shown a positive relationship between EO and performance appears to exist. However, an important question that remains unanswered is what effect EO might have on firm performance during periods of economic crisis, and the severe environmental turbulence that accompany such crises. This research is a first investigation towards the effects of EO on the performance of small and medium sized firms during the current global economic crisis. In this study we use the multidimensional model of EO and test a series of hypotheses pertaining to its performance effects using survey data gathered from 164 Dutch SMEs. The present research shows that proactive firm behavior positively contributes to SME performance during the economic crisis. We further show that innovative SMEs do perform better in turbulent environments, but those innovative SMEs should minimize the level of risk and should take action to avoid projects that are too risky

Modeling human perceptual thresholds in self-motion perception

Knowledge of thresholds for perception of inertial motion is needed for the design of simulator motion filters. Experiments have generally been done to measure these thresholds in isolation, one motion at the time. In vehicle simulation however, several motions occur concurrently. In a flight simulator, both inertial and visual cues are provided and motion is rarely in a single axis. Previous experiments have shown that inertial thresholds are modified when simultaneous inertial cues or visual and inertial cues are provided. In this paper, pitch motion thresholds are measured for 5 frequencies between 0.6 and 10 rad/s. Thresholds are measured in two situations: in the dark, single axis motion (sensory thresholds) and in the dark, with a heave masking cue (indifference thresholds). The heave motion has an amplitude of 0.02 g and is of the same frequency as the pitch motion. The effect of the masking cue on the pitch rate perception threshold frequency description is not significant. The measured thresholds, both with and without masking cue, fit known models for the Semi-Circular Canals transfer function