Motion Sensitivity, Nighttime Driving, and Age   

Paul B Freeman OD, FAAO, FCOVD   

 Driving is an extremely complex process which, if mismanaged, can be devastating
for those inside as well as outside the vehicle.
Consequently, some drivers (specifically, older drivers) self-select those situations in which they feel driving is safest, avoiding possible risky situations like rush hour traffic, inclement weather, and nighttime driving, to name but a few.
The latter situation is the topic of an article published recently by Wood and colleagues in Ophthalmic and Physiological Optics, specifically concerning pedestrian safety as it relates to their visibility at nighttime.

 To determine which visual components might be important for safe nighttime driving, the authors set up a two-part process.

The first was to assess young and senior individuals for visual acuity with habitual correction, contrast sensitivity function, useful field of view (UFOV), and motion sensitivity (with a test designed by the researchers).
It is somewhat intuitive that the test results would be worse for seniors, which they were.
Interestingly, however, the authors found that, after statistically removing age as a variable, motion sensitivity was an important independent variable, suggesting that being aware of motion is important at any age.
The remaining age-dependent variables rested on speed of visual processing and reaction time, measured by the UFOV; specifically, the subtest of selective visual processing.

The second part of the experimental assessment was to put these individuals on a closed road course and have them drive, determining at what distance they could see a pedestrian.
To make the task more “relevant to every day driving,” auditory and visual distractors were added to some of the laps driven.
The pedestrians were visible either by wearing “a fluorescent yellow vest with 50 mm wide silver retro-reflective material on the shoulders, front and back in a U shaped pattern,” or the same outfit but “with the addition of 50 mm wide silver retro-reflective strips surrounding the elbows, wrists, ankles, and knees.”
To me, the message was quite clear: because motion sensitivity is age-independent, regardless of whom the driver is, pedestrians at night should wear reflective materials, especially on their arms and legs.  
Presently, every state has a static visual acuity requirement for qualifying for a driver’s license.
Visual field requirements vary from state to state, with some states not requiring these measurements at all.
Adding a test for motion sensitivity to the mix is undoubtedly an important goal, especially as it relates to nighttime driving, but more research to standardize testing and establish normative values will be necessary.

Unfortunately, based on the fact that other testing that has been shown to correlate to safety and crash data (ie, contrast sensitivity function, and UFOV) is still not a part of any state testing protocol, motion sensitivity will not likely be incorporated into formal driving anytime soon.
Nevertheless, this information is important for eye care practitioners to be aware of, especially when counseling older adults about driving in general and, based on this data, nighttime driving more specifically.
The authors are to be commended on furthering our understanding of motion sensitivity as it relates to pedestrian awareness during nighttime driving.

References Wood JM, Lacherez P, Tyrrell RA.
Seeing Pedestrians at Night: Effect of Driver Age and Visual Abilities
[published online ahead of print June 2, 2014]. Ophthalmic Physiol Opt. DOI: 10.1111/opo.12139.