Visual perception of spatial relations in depth

The visual perception of spatial relations of two objects was investigated in a series of experiments. We examined spatial and contextual parameters. The effect of spatial parameters was investigated with various two-dimensional tasks: an exocentric pointing task, a parallelity task and a collinearity task. Whereas spatial parameters like relative distance and visual angle influenced the settings of all observers in a similar way, there were differences between tasks in their dependence on different parameters. For example, whereas the settings of the other tasks were dependent on the relative distance the settings of the parallelity task were not. This can be explained by different task-demands that are specific for each of these tasks. In the exocentric pointing task an observer has to direct a pointer, with a remote control, towards a target. We expanded the exocentric pointing task to a three dimensional version in which the height was also varied. Therefore, we had two dependent variables: the deviations in the horizontal plane (slant) and in the vertical plane (tilt). With this extension of the task, we could conclude that visual space is anisotropic since in contrast to the slant the tilt was not dependent on the relative distance. Another three-dimensional task that has been used is the ball-in-plane task, a task in which the observer has to hang a ball in a plane defined by three other balls by adjusting it in height. We found settings that were best described as concave settings, which is in agreement with most conclusions of the work described above. Furthermore, we investigated the effects of context on the 3D exocentric pointing task. We tested whether the settings of the observer were dependent on an egocentric reference like frontoparallelity or an allocentric reference like parallelity to a wall. It turns out that people differ in the references they use to do the task. However, in another experiment, we concluded that a reference like one's own body position is impossible to ignore. Thus, it seems that cues that are really prominently present will be used by all observers, whereas for less prominent cues people can choose to use them or not. In conclusion, spatial parameters seem to affect all observers in a similar way, whereas contextual parameters can affect observers differently

Effects of context on a visual 3-D pointing task

We examined the effects of egocentric and contextual references on a 3-D exocentric pointing task. Large systematic deviations were found for the slant (angle in the horizontal plane). For most observers, the deviations were smaller when the veridical pointing direction was parallel to a wall. For some observers the size of the deviations was also dependent on whether the veridical pointing direction was frontoparallel or not. For the tilt (angle in the vertical plane), the deviations were smaller and less systematic. Hence, although observers show compar- able systematic deviations, the way in which the presence of structure in an environment is used for judging positions of objects is observer-dependent

Visual space under free viewing conditions

Most research on visual space has been done under restricted viewing conditions and in reduced environments. In our experiments, observers performed an exocentric pointing task, a collinearity task, and a parallelity task in a entirely visible room. We varied the relative distances between the objects and the observer and the separation angle between the two objects. We were able to compare our data directly with data from experiments in an environment with less monocular depth information present. We expected that in a richer environment and under less restrictive viewing conditions, the settings would deviate less from the veridical settings. However, large systematic deviations from veridical settings were found for all three tasks. The structure of these deviations was task dependent, and the structure and the deviations themselves were comparable to those obtained under more restricted circumstances. Thus, the additional information was not used effectively by the observers

Horizontal-vertical anisotropy in visual space

We investigated the structure of visual space with a 3D exocentric pointing task. Observers had to direct a pointer towards a ball. Positions of both objects were varied. We measured the deviations from veridical pointing-directions in the horizontal and vertical planes (slant and tilt resp.). The slant increased linearly with an increasing horizontal visual angle. We also examined the effect of relative distance, i.e. the ratio of the distances between the two objects and the observer. When the pointer was further away from the observer than the ball, the observer directed the pointer in between himself and the ball, whereas when the pointer was closer to the observer he directed the pointer too far away. Neither the horizontal visual angle nor the relative distance had an effect on the tilt. The vertical visual angle had no effect on the deviations of the slant, but had a linear effect on the tilt. These results quantify the anisotropy of visual space

De toedracht van dodehoekongevallen en maatregelen voor de korte en lange termijn : een ongevallenanalyse over de jaren 1997-2007, verkeersobservaties en enquêtes onder fietsers en vrachtautochauffeurs + Bijlagenrapport.

SWOV has studied the circumstances of blind spot crashes and has looked for solutions and measures that can reduce the number of blind spot crashes. One of the reasons for this study was a discussion in Dutch Parliament about the blind spot issue. The design and the realization of the study were closely tuned with the Ministry of Transport. Elaborate consultations were also held with other interested parties. The Netherlands has been struggling with the blind spot issue for many years now: serious crashes involving lorries turning right and cyclists going straight ahead. In the last decades, the European Union has introduced several measures for lorries to prevent this type of crash: in the 1980s the close proximity mirror (Class V in Directive 2003/97/EC) was made compulsory, and side underrun protection in 1995. In 2003, the Netherlands was first to introduce the wide angle mirror (Class IV in Directive 2003/97/EC); Denmark and Belgium followed a year later. This measure was specifically intended for countries with many cyclists. The Netherlands still counts an average of 15 fatalities per year despite these measures. Although the numbers of fatalities showed a temporary considerable reduction in the years 2002 and 2003, this study shows that this was the case for all crash types involving both lorries and cyclists. This may however be due to the general attention for crashes involving lorries when the wide angle mirror was introduced, and not be caused by the mirror itself. Each blind spot crash causes social unrest because of the severity of the crash and the notion that there must be ways to prevent this type of crash. The study is based on analyses of serious blind spot crashes in the period 1997-2006, and on police reports from the years 2006 and 2007. The detailed crash data from the police reports were supplemented with survey data acquired from surviving cyclists and lorry drivers who had been involved in blind spot crashes. Traffic observations were also made at the locations were these crashes had occurred. Both groups of road users were interviewed to gain insight in the way cyclists and lorry drivers deal with the blind spot problem in daily practice. In addition, the everyday traffic situation was observed and, in the cab, the lorry drivers' actual behaviour was studied. This repor

Exocentric pointing in depth

An exocentric pointing task was used to compare the indicated pointing directions under exchange of target and pointer. Such a pair of pointing directions, together with the pointer and target locations, specifies a unique cubic arc. Such an arc may assume one of two qualitatively different shapes, namely a ‘‘C-arc’’ (constant sign of curvature) or an ‘‘S-arc’’ (containing a point of inflection between the endpoints). We show that human observers most often produce S-curves. This is of fundamental importance, since—in case one interprets the curve as an empirically determined ‘‘pregeodesic’’ (‘‘shortest connection’’, or ‘‘straight’’ connection in visual space)—it would imply that ‘‘visual space’’ in the strict geometrical sense is a non-entity. The experiments were performed in the outside environment, under normal daylight conditions, for distances ranging from one to over thirty meters. The implications of these data are discussed and possible ways to extend the restricted notion of ‘‘visual space’’ (e.g., as advocated by Luneburg) such as to allow one to account for the present results are suggested. Such extensions of the visual space concept include the local adjustment of geometrical structure in regions adjacent to the fixation direction

Prediction of fitness to drive in patients with Alzheimer's dementia.

The number of patients with Alzheimer’s disease (AD) is increasing and so is the number of patients driving a car. To enable patients to retain their mobility while at the same time not endangering public safety, each patient should be assessed for fitness to drive. The aim of this study is to develop a method to assess fitness to drive in a clinical setting, using three types of assessments, i.e. clinical interviews, neuropsychological assessment and driving simulator rides. The goals are (1) to determine for each type of assessment which combination of measures is most predictive for on-road driving performance, (2) to compare the predictive value of clinical interviews, neuropsychological assessment and driving simulator evaluation and (3) to determine which combination of these assessments provides the best prediction of fitness to drive. Eighty-one patients with AD and 45 healthy individuals participated. All participated in a clinical interview, and were administered a neuropsychological test battery and a driving simulator ride (predictors). The criterion fitness to drive was determined in an on-road driving assessment by experts of the CBR Dutch driving test organisation according to their official protocol. The validity of the predictors to determine fitness to drive was explored by means of logistic regression analyses, discriminant function analyses, as well as receiver operating curve analyses. We found that all three types of assessments are predictive of on-road driving performance. Neuropsychological assessment had the highest classification accuracy followed by driving simulator rides and clinical interviews. However, combining all three types of assessments yielded the best prediction for fitness to drive in patients with AD with an overall accuracy of 92.7%, which makes this method highly valid for assessing fitness to drive in AD. This method may be used to advise patients with AD and their family members about fitness to drive. (Author/publisher

Prediction of Fitness To Drive in Patients with Alzheimer’s Dementia

The number of patients with Alzheimer’s disease (AD) is increasing and so is the number of patients driving a car. To enable patients to retain their mobility while at the same time not endangering public safety, each patient should be assessed for fitness to drive. The aim of this study is to develop a method to assess fitness to drive in a clinical setting, using three types of assessments, i.e. clinical interviews, neuropsychological assessment and driving simulator rides. The goals are (1) to determine for each type of assessment which combination of measures is most predictive for on-road driving performance, (2) to compare the predictive value of clinical interviews, neuropsychological assessment and driving simulator evaluation and (3) to determine which combination of these assessments provides the best prediction of fitness to drive. Eighty-one patients with AD and 45 healthy individuals participated. All participated in a clinical interview, and were administered a neuropsychological test battery, and a driving simulator ride (predictors). The criterion fitness to drive was determined in an on-road driving assessment by experts of the CBR Dutch driving test organisation according to their official protocol. The validity of the predictors to determine fitness to drive was explored by means of logistic regression analyses, discriminant function analyses, as well as receiver operating curve analyses. We found that all three types of assessments are predictive of on-road driving performance. Neuropsychological assessment had the highest classification accuracy followed by driving simulator rides and clinical interviews. However, combining all three types of assessments yielded the best prediction for fitness to drive in patients with AD with an overall accuracy of 92.7%, which makes this method highly valid for assessing fitness to drive in AD. This method may be used to advise patients with AD and their family members about fitness to drive

Assessing fitness to drive : a validation study on patients with mild cognitive impairment.

There is no consensus yet on how to determine which patients with cognitive impairment are able to drive a car safely and which are not. Recently, a strategy was composed for the assessment of fitness to drive, consisting of clinical interviews, a neuropsychological assessment, and driving simulator rides, which was compared with the outcome of an expert evaluation of an on-road driving assessment. A selection of tests and parameters of the new approach revealed a predictive accuracy of 97.4% for the prediction of practical fitness to drive on an initial sample of patients with Alzheimer’s dementia. The aim of the present study was to explore whether the selected variables would be equally predictive (i.e., valid) for a closely related group of patients; that is, patients with mild cognitive impairment (MCI). Eighteen patients with mild cognitive impairment completed the proposed approach to themeasurement of fitness to drive, including clinical interviews, a neuropsychological assessment, and driving simulator rides. The criterion fitness to drive was again assessed bymeans of an on-road driving evaluation. The predictive validity of the fitness to drive assessment strategy was evaluated by receiver operating characteristic (ROC) analyses. Results showed that twelve patients with MCI (66.7%) passed and 6 patients (33.3%) failed the on-road driving assessment. The previously proposed approach to the measurement of fitness to drive achieved an overall predictive accuracy of 94.4% in these patients. The application of an optimal cutoff resulted in a diagnostic accuracy of 100% sensitivity toward unfit to drive and 83.3% specificity toward fit to drive. Further analyses revealed that the neuropsychological assessment and the driving simulator rides produced rather stable prediction rates, whereas clinical interviews were not significantly predictive for practical fitness to drive in the MCI patient sample. The authors concluded that the selected measures of the previously proposed approach revealed adequate accuracy in identifying fitness to drive in patients with MCI. Furthermore, a combination of neuropsychological test performance and simulated driving behavior proved to be the most valid predictor of practical fitness to drive. (Author/publisher