The effects of demographics, functioning, and perceptions on the relationship between self-reported and objective measures of driving exposure and patterns among older adults.

The exploratory study reported here was intended to examine: how strongly subjectively reported driving avoidance behaviors (commonly referred to as self-regulation) and exposure were related to their objectively measured counterparts and whether it depended on the specific behavior; the extent to which gender and age play a role in the association between subjectively reported driving avoidance behaviors and exposure and their objectively measured counterparts; and the extent to which demographics, health and functioning, driving-related perceptions, and cognition influence the association between subjective and objective driving avoidance behaviors overall. The study used data from the Longitudinal Research on Aging Drivers (LongROAD) study, a multisite, prospective cohort study designed to generate empirical data for understanding the role of medical, behavioral, environmental, and technological factors in driving safety during the process of aging. Objective driving measures were derived from GPS/datalogger data from 2131 LongROAD participants' vehicles. The corresponding subjective measures came from a comprehensive questionnaire administered to participants at baseline that asked them to report on their driving exposure, patterns, and other aspects of driving. Several other variables used in the analyses came from the comprehensive questionnaire and an inperson clinical assessment administered to participants at baseline. A series of simple linear and logistic models were fitted to examine the relationship between the subjective and objective driving measures of interest, and a multivariable analysis was conducted to examine the potential role of selected factors in the relationship between objective and subjective driving avoidance behaviors. Results of the models are presented and overall findings are discussed within the context of the existing research literature.

Restraint use patterns for older child passengers in Michigan.

The purpose of the present study was to conduct the first statewide direct observation survey of restraint use designed specifically for older child passengers (4-15 years of age). We also sought to determine the factors that were related to belt use by older child passengers in Michigan so that effective programs could be developed to promote use of restraint devices in this age group. The study found that older child restraint use was about 58% statewide. Restraint use was highest in regions where overall belt use was higher, when the driver was using a safety belt, in sport utility vehicles and vans/minivans, and in the front-right seating position. No difference in restraint use was found for the day of week, the sex of the child, or the type of site where data was collected. The study provides the largest scale analysis to date on older child occupant restraint use patterns. The data provide some much needed empirical data on the restraint use patterns of older child passengers for development of theory to better understand and predict lack of restraint use in this age group.

Trends in driver and front-right passenger safety belt use in Michigan: 1984-1998.

As part of Michigan's effort to track trends in safety belt use within the state over time, the University of Michigan Transportation Research Institute conducted 20 statewide surveys of safety belt use between 1984 and 1998. Results indicate that Michigan safety belt use trends for drivers and front-right passengers are similar to other statewide and national trends. Belt use in Michigan increased dramatically immediately after the state implemented its mandatory belt use law (secondary enforcement) followed by a smaller decline that leveled off at a rate more than 20 percentage points higher than before the law. Belt use was consistently higher among drivers than front-right passengers, older than younger front-outboard occupants, females than males, and front-outboard occupants exiting freeways than those stopped at local intersections. Examination of belt use trends in Michigan provides useful information for continued efforts to increase belt use in our state and for all states interested in meeting national goals for safety belt use for the year 2000 and beyond.

A statewide analysis of child safety seat use and misuse in Michigan.

This study was designed to determine frequency of child safety seat use for children under the age of 4 years in Michigan, as well as to determine types of misuse. No state has previously conducted such a statewide survey. A two-stage sampling plan was used with data collected through direct observation at a sample of 88 child-care centers and pediatric clinics throughout the state. Misuse data were collected at a subset of the sites through driver interview and visual and hands-on inspection. The study results indicate that 74.5% of children under 4 years of age in Michigan are in safety seats with use highest in vehicles driven by belted drivers, females, and drivers under 60 years of age. Some degree of seat misuse was found in 88.5% of the inspections. The most common types of misuse were related to snugness of fit (both in installing the seat into the vehicle and in securing the child), use of the safety belt locking clip, and the harness positioning clip. Drivers who had a high occurrence of misuse, as compared with drivers with lower misuse, had lower educational levels, removed the seat frequently from their vehicle, were not the parent of the child, and had children who were both younger and smaller. The results show that efforts to encourage people to use child safety seats have been successful.

Measures of perceived linear size, sagittal motion, and visual angle from optical expansions and contractions.

Using monocular observation, open-loop measurements were obtained of the perceptions of linear size, angular size, and sagittal motion associated with the terminal (largest or smallest) stimuli of repetitive optical expansions and contractions using 1-D or 2-D displays produced on a video monitor at a constant distance from the observer. The perceptions from these dynamic conditions were compared with those from static conditions in which the stimuli were of the same physical size and at the same physical distance as the terminal dynamic stimuli, but that were not part of the optical expansions or contractions. One result, as expected, was that the measures of perceived linear and angular size differed, but also, unexpectedly, some substantial errors were associated with the measures of perceived angular size. Another result was that the amount of size constancy was considerably less than was expected from the obtained amount of perceived motion in depth. Consistent with the latter result, it was found that the size-distance invariance hypothesis (SDIH), using the physical visual angles of the terminal stimuli, predicted only about half of the perceived motion in depth obtained with the dynamic changes. Using the obtained measures of perceived visual angles in the SDIH increased rather than decreased the error in predicting the amount of motion in depth as perceived. An additional experiment suggests that at least some of the error in the measurement of the perceived visual angle is a consequence of error in the perceived origin of the visual angles. The absence of the expected relation between size constancy and perceived motion in depth in the dynamic conditions is hypothesized to be due to cognitive processes associated with off-sized perceptions of the stimuli.

A comparison of two direct-observation methods for measuring daytime safety belt use.

This study compared two methods for measuring front-outboard shoulder-belt use: looking into vehicles when they stopped at a traffic control device (SVDO) and looking into vehicles as they traveled along a traffic corridor (MVDO). The reliability of the latter method has been questioned and certain surveys, such as the National Occupant Protection Use Survey (NOPUS), use both methods to estimate safety belt use. In one experiment, the methods were compared on overall belt use rates and reliability. A second experiment investigated the effect that vehicle speed had on an observer's ability to measure accurately belt use using the MVDO method. The results showed that daytime belt use rates between methods were nearly identical and inter-method reliability was quite high, indicating that front-outboard shoulder-belt use can be measured identically with either method. The second experiment showed that measurement accuracy was not affected by vehicle speeds of up to 60 mph and that overall accuracy was above 95%.

Perceptual collapse of three-dimensional structure from motion parallax.

This study concerned how perceived depth collapses after asymptotic depth is reached and the information specifying depth is abruptly removed. The stimuli were random-dot, computer-generated three-dimensional objects and the depth information was motion parallax. Motion parallax was removed in two ways. In the first method, the depth of all object points was reassigned to zero, simulating a disk. In the second method, a rotation of the object was introduced in such a way that a degenerate case of motion parallax was produced. The results showed that judgments of depth slowly collapsed once motion parallax was removed. Over-all, judgments of depth required about the same duration to collapse as was required for the judgments to build up to asymptotic levels (about 750 msec.). Finally, depth collapsed more slowly when the motion parallax was removed by redefining the object as a disk than when removed using the other method.

The perceptual flattening of three-dimensional scenes enclosed by a frame.

The effects of a visible frame around a three-dimensional scene on perceived depth within the scene was investigated in three experiments. In experiment 1 subjects judged the slant of an object that had been rotated about a vertical axis. Judged slant was reduced when the frame was illuminated. In experiments 2 and 3 subjects judged the shape (width-to-height ratio) of the object. The object was judged to be narrower when the frame was illuminated (experiment 2) or when a frame was added to the scene in an illuminated room (experiment 3). These results demonstrate that the presence of a frame around a three-dimensional scene serves as a flatness cue, reducing perceived depth within the scene.

The spatial and temporal characteristics of perceiving 3-D structure from motion.

In four experiments, a scalar judgment of perceived depth was used to examine the spatial and temporal characteristics of the perceptual buildup of three-dimensional (3-D) structure from optical motion as a function of the depth in the simulated object, the speed of motion, the number of elements defining the object, the smoothness of the optic flow field, and the type of motion. In most of the experiments, the objects were polar projections of simulated half-ellipsoids undergoing a curvilinear translation about the screen center. It was found that the buildup of 3-D structure was: (1) jointly dependent on the speed at which an object moved and on the range through which the object moved; (2) more rapid for deep simulated objects than for shallow objects; (3) unaffected by the number of points defining the object, including the maximum apparent depth within each simulated object-depth condition; (4) not disrupted by nonsmooth optic flow fields; and (5) more rapid for rotating objects than for curvilinearly translating objects.

Perceptual linkage of multiple objects rotating in depth.

When multiple objects rotate in depth, they are frequently perceived to rotate in the same direction even when perspective information signals counterrotation. Three experiments are reported on this tendency to recover the rotation directions of multiple objects in a nonindependent fashion (termed rotational linkage). Rotational linkage was strongly affected by slant in depth of the objects, image perspective, and relative starting phase of the objects. Linkage was found not to vary as a function of the relative rotation speed of the objects or the relative alignment of their rotation axes. Rotational linkage is interpreted as a tendency of the visual system to assign signed depths to objects based on a communality of image point direction.