The effects of age on driving performance and visual behaviour

Much like novice drivers, drivers who are aged 65 or above are at a higher risk of being

injured or killed on the road (Evans, 2000). In the United States for example, in 2012, 5,560

people who were over 65 were killed and another 214,000 were injured (U.S Department of

Transportation, 2014). Age related-decline in perceptual, visuomotor and cognitive abilities

have been well documented (Birren & Schaie, 2001; Salthouse, 2009; Shanmugaratnam, Kass,

& Arruda, 2010), and it is likely that these impairments contribute to the increased number of

accidents we observe in an older adult population (Anstey et al., 2012; Anstey, Wood, Lord, &

Walker, 2005; McGwin & Brown, 1999). This section will provide a brief overview of the eye

movements differences that are known to exist between older adult populations and younger

adult populations of drivers, which will hopefully provide insights into what makes older

drivers an ‘at-risk’ population. It will explore the hazard perception skill of older adults before exploring older adults’ attentional functioning and how this contributes to their driving performance. It will then discuss the research pertaining to older adults’ eye movements and driving.

1.4.1 Older adults’ driving performance, hazard perception skill and cognitive ability

Throughout the literature, there are two key differences in driving behaviour that are

consistently identified that are in-line with typical age-related deficits. The first is that older

adults typically exhibit less safe driving. This includes driving slower, poorer lane positioning

and making more driver errors (Aksan et al., 2012; Bunce, Young, Blane, & Khugputh, 2012;

32 Wilkie, 2012). The second is that, although they are just as likely to inspect hazardous areas

and hazards, older adults are typically slower to respond to them (Borowsky et al., 2010;

Horswill et al., 2008; Horswill et al., 2009). It therefore makes sense that this population is at

an increased risk for accident involvement.

What is it that contributes to the typical poorer patterns of behaviour identified? One of the

main suggestions that has been explored relates, again, to cognitive and attentional function.

Several studies have demonstrated how the cognitive demands of driving influence older

adults’ driving performance. Chaparro, Wood, and Carberry (2004), found that inducing a higher cognitive load using verbal or visual tasks while driving negatively influenced older

adults’ driving performance. Compared to young adults, they were less able to detect road signs

and took longer to complete the drives. Schwarze, Ehrenpfordt, and Eggert (2014) found that

the mental workload experienced, as measured by cardiac output, was higher for older drivers

during difficult driving situations compared to younger adults (e.g. complex, multi-lane turns).

Moreover, the UFOV task has been widely used to assess attentional performance in older

adults. Performance in the UFOV is often poorer in older adults (Clay et al., 2005; Rogé,

Ndiaye, & Vienne, 2014) and thus they have deficits in attentional function. Poorer

performance on this task seems correlated with increased crash risk (Bruni & Roenker, 1993;

Owsley, Ball, Sloane, Roenker, & Bruni, 1991) and general driving performance in older adults

(Cushman, 1996; Roenker, Cissell, Ball, Wadley, & Edwards, 2003; Wood & Troutbeck,

1995). It is likely that the impairment in attentional function is a direct factor leading to poorer

driving ability, where, for example, older adults may not have the attentional capacity to attend

to multiple objects at once or process hazard information as fast (Horswill et al., 2008). The

opposite is also true. For example, older adults with better attentional function are better at

anticipating hazardous events than older drivers with poorer functioning (Andrews &

Westerman, 2012). But how does their cognitive and attentional capabilities relate to eye

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1.4.2 Older adults’ eye movements and driving

Given the limitations to older adults’ attentional functioning, are there eye movement

differences in an older population compared to younger adults when driving? Surprisingly,

there are few studies which address this in either a) a naturalistic driving setting which

incorporates active control of a vehicle or b) under non-hazardous driving conditions.

An early study investigating eye movement differences in older adults comes from Maltz and

Shinar (1999). In their second experiment, older adults and younger participants had to inspect

static images of driving scenes as if they were the driver. They found evidence to suggest that

older adults had a more impoverished visual search, including smaller saccades and increased

number of fixations. They also found that the younger participants were better able to distribute

eye movements more evenly across the scene and made less re-fixations to certain locations.

However, since general visual search is typically impaired in older adults (Ball, Beard,

Roenker, Miller, & Griggs, 1988), it can be argued that these findings are simply a product of

a poorer general visual search capacity and may have little relevance to eye movements and

driving in real life situations.

Older adults’ eye movements have since been tracked while they watch videos of driving

scenes, but it is difficult to consistently identify general patterns of fixations made. Underwood,

Phelps, Wright, Van Loon, and Galpin (2005) found that there was very little difference in scan

patterns between younger and older drivers when watching video clips – both during non-

hazardous events and hazardous events. This included no differences in scanning of the

roadway and inspection times. Thus, there were no observed effects of age-related decline in

viewing driving clips. However, Yeung and Wong (2015) found the opposite during a similar

video task, where older adults typically scanned the roadway less than younger adults. It would

appear that more research is required to identify if there are age-related eye movement

34 More promising evidence for highlighting the differences in eye movement behaviour comes

from research investigating older adults’ eye movements during specific real or simulated driving events, namely; tackling intersections. Romoser and Fisher (2009) and Romoser,

Pollatsek, Fisher, and Williams (2013) identified that during simulated driving, older drivers

were less likely to scan the roadway (at least any more than once) and adjacent lanes when

tackling intersections. Romoser et al. (2013) proposed that this inability to search appropriately

is because older adults prioritise the need to monitor vehicle control. Supporting this, Min,

Min, and Kim (2013) found that older drivers tended to fixate more on the direction of the turn

rather than anywhere else compared to younger drivers. Dukic and Broberg (2012) found

evidence that older drivers tended to fixate on road markings to help with positioning and

manoeuvring when approaching intersections, whereas younger drivers were more likely to

fixate on potential hazardous objects such as moving cars. In addition, they also found that

older drivers took longer to make an initial fixation to the intersection and had longer average

fixation durations during inspection. This also suggests an impairment in planning and

processing the information at an intersection. Together, these findings highlight that

impairment in attentional processing may in fact limit effective eye movement behaviour in

older adult drivers – at least when navigating intersections.

However, it still remains to be seen if there are differences in eye movements during normal

driving situations. Thus, an experiment is described in Chapter 5 which explores the possible

differences in eye movement behaviour and driving performance between older adult drivers

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