Behavioral Entropy as a Measure of Driving Performance

Delayed event detection and degraded vehicle control are observed when drivers fuel their need to perform extra-driving activities. Vehicle control and event detection are shown to degrade most if the in-vehicle task requires spatial cognitive resources and/or if the activity requires visual perception and/or manual control manipulation. In-vehicle tasks with auditory input and/or voice output that primarily demand low levels of verbal cognitive resources appear to affect event detection only to a small degree and seem to have no effect on vehicle control. A theory-based approach to measure, analyze, and interpret these performance assessments. Results from our SAE paper #1999-01-0892 are used as a vehicle to demonstrate that steering entropy (a measure of vehicle control) in conjunction with reaction times to unpredictable peripheral events (a surrogate measure for event detection) offer clear insight into the safety consequences of various in-vehicle tasks. These results are here discussed in the context of a simple linear predictive model that is based on Wickens’ theory of multiple resources. The model is shown to offer useful predictions about and interpretations of the effects that various in-vehicle tasks have on driving performance in general and driver distraction in particular

Steering Entropy Revisited

Drivers aim to maintain their vehicle within a number of individualsituated safety margins. Safety margin violations are characterized by rapid strongcorrective steering. Steering entropy was introduced to quantify drivers’ efforts tomaintain their lateral safety margins. In the original steering entropy, severalcomputational assumptions were made. The objective is to scrutinize andmotivate these choices and exemplify the effects of deviations from these choiceswith data from a driver distraction study. The new optimized algorithm is shownto yield significances where a number of classical metrics fail to find anysignificance. Its sensitivity is attributed to the fact that a number of observedchanges in steering behavior all manifest in a widened steering prediction errordistribution which the algorithm picks up sensitively with its log-based weightingof prediction error outliers and its use of a prediction filter that is maximallysensitive to the spectral characteristics of the baseline data

Event-Based Driver Performance Assessment

Driving is an intermittent control task during which drivers manage their work across a number of driving and non-driving sub-tasks. The multitasking nature forces drivers to adopt situated safety margins (tolerances) in terms of time-headway (THW), time-to-collision (TTC), time-to-linecrossing (TLC), etc. Unacceptable situations (i.e. violations of safety margins defined here as events) are characterized by corrective maneuvers or actions. The frequency with which corrective actions are necessary (bandwidth), the hazard level of the situation that inspired these actions (performance), and the rate and magnitude of the responses to these situations (effort) provide a rich signature of how drivers manage their task(s). We hypothesize that drivers’ perception of performance and effort are founded in the characteristics of experienced events. This is explored by comparing driving characteristics of bus drivers who drive on the shoulder of a highway with and without the support of a haptic lateral support system (LSS). Subjective performance and effort scores extracted from a usability questionnaire and objective ones from our event-based analysis show highly significant correspondence when comparing supported versus unsupported driving. This provides validating support for the adopted event-based approach. The proposed approach offers not only sensitive metrics of driver performance and effort to evaluate ITS applications but also explanatory power by exposing the various strategically different ways drivers are affected by these systems. This method of quantifying and analyzing driver data affords new opportunities to evaluate driver responses to ITS applications

Event-Based Driver Performance Assessment

Driving is an intermittent control task during which drivers manage their work across a number of driving and non-driving sub-tasks. The multitasking nature forces drivers to adopt situated safety margins (tolerances) in terms of time-headway (THW), time-to-collision (TTC), time-to-linecrossing (TLC), etc. Unacceptable situations (i.e. violations of safety margins defined here as events) are characterized by corrective maneuvers or actions. The frequency with which corrective actions are necessary (bandwidth), the hazard level of the situation that inspired these actions (performance), and the rate and magnitude of the responses to these situations (effort) provide a rich signature of how drivers manage their task(s). We hypothesize that drivers’ perception of performance and effort are founded in the characteristics of experienced events. This is explored by comparing driving characteristics of bus drivers who drive on the shoulder of a highway with and without the support of a haptic lateral support system (LSS). Subjective performance and effort scores extracted from a usability questionnaire and objective ones from our event-based analysis show highly significant correspondence when comparing supported versus unsupported driving. This provides validating support for the adopted event-based approach. The proposed approach offers not only sensitive metrics of driver performance and effort to evaluate ITS applications but also explanatory power by exposing the various strategically different ways drivers are affected by these systems. This method of quantifying and analyzing driver data affords new opportunities to evaluate driver responses to ITS applications

A Cybernetic Perspective on Car Following in Fog

Drivers often drive at a closer time headway (THW) in fog than in clear whether conditions for similar speed ranges (White & Jeffery, 1980). Closer following is generally considered more dangerous. The hypothesis pursued in this paper is that drivers experience a perceptual-motor benefit from driving closer in fog that results in greater (or equivalent) safety and reduced driving demand. A computational car following model with an experimentally constructed perceptual module is introduced and used to demonstrate that under some conditions, closer following in fog is indeed beneficial because it effectively reduces drivers’ perceptual delay by a sufficient amount to improve controllability of the gap so much that the variability in THW reduces more than (or as much as) the adopted decrease in target THW

A numerical study of a method for measuring the effective in situ sound absorption coefficient

The accuracy of a method [Wijnant et al., “Development and applica- tion of a new method for the in-situ measurement of sound absorption”, ISMA 31, Leuven, Belgium (2010).], for measurement of the effective area-averaged in situ sound absorption coefficient is investigated. Based on a local plane wave assump- tion, this method can be applied to sound fields for which a model is not available. Investigations were carried out by means of finite element simulations for a typical case. The results show that the method is a promising method for determining the effective area-averaged in situ sound absorption coefficient in complex sound fields

Reaching the hearts and minds of illiterate women in the Amhara highland of Ethiopia:Development and pre-testing of oral HIV/AIDS prevention messages

In the style of radio programmes, we developed three episodes of audio HIV prevention education for illiterate women in Ethiopia. We used social-oriented presentation formats, such as discussion between women on HIV prevention, and expert-oriented presentation formats, such as an interview with a male doctor. The aim of this study was to assess the relation between evaluation of presentation formats and overall liking of episodes, which is important for persuasive effects. Thirty women from rural Amhara listened to the episodes and, after listening, female data collectors interviewed the women on evaluation of presentation formats, overall liking of episodes, identification with the characters and convincingness. Evaluation of social-oriented presentation formats was strongly related to overall liking of episodes, but evaluation of expert-oriented presentation formats was not. This relation was mediated through convincingness and not through identification. We conclude that social-oriented presentation formats make messages more convincing and, consequently, improve overall liking and persuasive impact

Wayfinding and Glaucoma: A Virtual Reality Experiment.

PurposeWayfinding, the process of determining and following a route between an origin and a destination, is an integral part of everyday tasks. The purpose of this study was to investigate the impact of glaucomatous visual field loss on wayfinding behavior using an immersive virtual reality (VR) environment.MethodsThis cross-sectional study included 31 glaucomatous patients and 20 healthy subjects without evidence of overall cognitive impairment. Wayfinding experiments were modeled after the Morris water maze navigation task and conducted in an immersive VR environment. Two rooms were built varying only in the complexity of the visual scene in order to promote allocentric-based (room A, with multiple visual cues) versus egocentric-based (room B, with single visual cue) spatial representations of the environment. Wayfinding tasks in each room consisted of revisiting previously visible targets that subsequently became invisible.ResultsFor room A, glaucoma patients spent on average 35.0 seconds to perform the wayfinding task, whereas healthy subjects spent an average of 24.4 seconds (P = 0.001). For room B, no statistically significant difference was seen on average time to complete the task (26.2 seconds versus 23.4 seconds, respectively; P = 0.514). For room A, each 1-dB worse binocular mean sensitivity was associated with 3.4% (P = 0.001) increase in time to complete the task.ConclusionsGlaucoma patients performed significantly worse on allocentric-based wayfinding tasks conducted in a VR environment, suggesting visual field loss may affect the construction of spatial cognitive maps relevant to successful wayfinding. VR environments may represent a useful approach for assessing functional vision endpoints for clinical trials of emerging therapies in ophthalmology

Steering Entropy Changes as a Function of Microsleeps

This study aimed to assess steering entropy as a measure of decrements in driving performance caused by microsleeps. Microsleeps are brief, unintended episodes of loss of attention that last 3-14 seconds. These episodes, which are frequent in drivers with sleep disorders, can be long enough to impact steering performance and are particularly disruptive when driver action is imperative, as when driving around curved highway segments. Steering entropy is a driver-centered performance measure that can detect drivers’ corrective responses to situations when the vehicle state falls outside the driver’s expectations. This study tests the hypothesis that steering entropy is an indicator of increased erratic steering behavior during microsleep episodes in drivers with obstructive sleep apnea/hypopena syndrome (OSAHS). Twenty-four drivers with OSAHS were used in this study and their electroencephalography (EEG) defined microsleep (cases) and non-microsleep episodes (crossover control) were compared using a case-crossover method. The performance measure, steering entropy, was calculated from a time-series history of steering angle data. Steering entropy was compared for each microsleep in the three-second interval both immediately preceding and immediately following each microsleep. Results showed that steering entropy was higher on curves during microsleeps and post microsleeps when compared to straight road segments and the no-workload baseline condition. This suggests that steering entropy can capture erratic steering behavior, allowing us to better understand how drivers correct for previous steering errors

Micromachining of buried micro channels in silicon

A new method for the fabrication of micro structures for fluidic applications, such as channels, cavities, and connector holes in the bulk of silicon wafers, called buried channel technology (BCT), is presented in this paper. The micro structures are constructed by trench etching, coating of the sidewalls of the trench, removal of the coating at the bottom of the trench, and etching into the bulk of the silicon substrate. The structures can be sealed by deposition of a suitable layer that closes the trench. BCT is a process that can be used to fabricate complete micro channels in a single wafer with only one lithographic mask and processing on one side of the wafer, without the need for assembly and bonding. The process leaves a substrate surface with little topography, which easily allows further processing, such as the integration of electronic circuits or solid-state sensors. The essential features of the technology, as well as design rules and feasible process schemes, will be demonstrated on examples from the field of ¿-fluidic