F. ANÁLISIS ESTADÍSTICO Y PRUEBAS DE SIGNIFICANCIA
1. Elaboración de mortadela de llama y alpaca
Many studies have examined older people’s self-reports of problems with memory and other cognitive lapses, and the results suggest a complex relationship between their beliefs and their functional performance. In this subsection, we begin by reviewing studies that have looked at awareness of declining visual attention. Some of these examine both perceptual and attentional measures, allowing comparison with the findings of the previous subsection.
Ball et al. (1998) revisited the Jefferson sample to examine the relationship between objectively measured functional impairment and driving patterns. Because most older drivers reported avoiding driving at night, it was not possible to gauge any link to impairment. However, avoiding driving at speed or in busy traffic correlated with objectively measured impairment of vision, visual attention (UFOV), and a measure of general cognitive function. Those who were impaired also reported driving fewer times in a week. Drivers with cataract problems were more likely than those without eye disease to avoid busy or fast traffic, and driving in rain or alone (see also
Marottoli et al., 1993). Older drivers with functional impairment were thus more likely to change driving behaviour, but as Ball et al. point out, given the design of the study, it is not possible to say that the impairment directly led to avoidance. Ball et al. (1998) also looked at relationships with accidents. They looked at accident records for the five years prior to assessment, and three subsequent years. Those who had experienced crashes in the previous five years were more likely to avoid driving in the rain, or in rush hour, and to avoid turns that involved crossing a traffic stream (i.e. left turns). This last point is interesting in the light of data that intersections are especially risky for older drivers (section 4.1). It could reflect accurate awareness of increased vulnerability and judgement of a particular source of risk, or because the accident history would often have involved intersection collisions, it may arise from a simpler mechanism of avoiding the specific situation that caused a previous accident. For subsequent accidents, there was no relationship with avoidance. Ball et al. pointed out that of the many in their sample who stopped driving altogether before the end of the three years, most had substantial functional impairment. This would have made it harder to detect a statistical link. Nevertheless, this study provides no direct evidence that the adjustments made by older drivers were effective in reducing accident risk.
Ball et al. (1998) did find a weak indication that older drivers with general cognitive impairment did not have as much insight into their difficulty as those with more specifically visual problems, for whom there was a closer match between degree of impairment and level of avoidance. Dubinsky et al. (1992) linked a lack of
awareness of driving impairment to cognitive decline. Cognitive impairment certainly does increase risk for drivers. AD is associated with an increased risk of fatality among older drivers (e.g. Johansson et al., 1997). Lundberg and Hakamies- Blomqvist (1998) compared older drivers with a history of at-fault crashes to other
older drivers and found they did less well on tests of visuo-spatial memory,
emphasising the relevance of subtle cognitive changes that may go unnoticed. Given that pedestrians have to deal with aspects of the same road environment as drivers, we would also expect cognitive decline to affect their safety.
In relation to cognitive problems, there is other evidence of a relative lack of insight. Rabbitt (1990) showed that whereas older people may be aware that reaction times slow with increasing age, they may not be aware of the extent to which their own reaction time has slowed, or of their errors in such reaction time tasks. Spackman (1986) reported that of the 27 older drivers in her survey, with an average age of 67 years, all believed they could concentrate on traffic as well as ever. Rabbitt et al. (1996) found that older drivers were typically unaware of problems identified by qualified instructors observing them, such as speed and distance judgements. In general, the evidence that visual attention problems (e.g. as measured by UFOV, see section 2) are associated with higher accident risk among drivers implies that drivers are either unaware of or unable to compensate for such deficiencies. Ball and
Owsley (1993, Jefferson sample) looked at a subset (14 people) who had poor UFOV scores, yet few crashes, and so appeared to be successfully compensating. On further investigation, they found that 10 of them also had poor eye health. They also found that those with poor eye health reported greater avoidance of difficult driving situations. Ball and Owsley (1993) speculated that perhaps these older drivers did not pick up their problems with attention but were aware of eye problems, which led them to regulate their driving.
McGwinn et al. (1998) asked drivers about their accidents over the past five years, and found that those who failed to report accidents that were recorded in official accident records also tended to have lower functional levels of contrast sensitivity and peripheral field sensitivity.
Mori and Mizohata (1995), reviewing several Japanese studies, found that older people who had stopped driving did not give functional impairment as a reason. In fact, they were more likely to stop driving if they lost access to parking space near home. Atkins (2001) also reported that 52% of older drivers surveyed in the UK gave parking as a particular difficulty, more than speed of traffic (15%), restrictions in their own physical movement (5%), or slowed response speed (4%). However, Mori and Mizohata observed that older drivers drove more slowly, and adopted a lane position further from other cars, suggesting that their driving style was more conservative. Indeed, greater age was associated with cessation, and Mori and Mizohata interpreted age as a proxy for increased ‘‘uneasiness’’ (p. 398). They concluded that older drivers, who estimated a younger age to cease driving for others than themselves, tried to compensate but either did not recognise, or were unwilling to act fully on, functional changes, resulting in an elevated accident risk. Mathey (1983b), discussing older German drivers reported similar changes in driving style, and a recent UK survey found that four in five older drivers preferred
to avoid driving long distances, at night, in bad weather, or in town centres (Atkins, 2001).
Lyman et al. (2001) studied driving habits among a large sample of older drivers in Mobile County, Alabama, and their relationship with the amount of driving and self- reported difficulty driving. For vision, cataracts and visual impairment were
associated with less driving, but only poor near vision was associated with significantly more self-reported difficulty. This suggests that some drivers were compensating for problems they were not aware of, or at least did not report. Other medical conditions, like stroke or kidney problems, were also associated with more experience of difficulty. These particular conditions are likely to produce highly noticeable symptoms. For cognitive impairment, there was no link with reported difficulty, and only a non-significantly increased likelihood of having a low annual mileage. These data are consistent with the conclusion that normally ageing older people become aware of some functional changes, but perhaps not all.
Cognitive functions such as planning and executive control are obviously important in the road environment, and we would expect impairment to affect skill. A
laboratory study by Brouwer et al. (1988) illustrated this. In a simulator, they found that older drivers could compensate for the effect of a sidewind, but could not adjust for such strong sidewinds as middle-aged drivers. Older drivers with better scores on laboratory measures of executive skills (e.g. planning and reasoning) and
information processing speed adjusted best.
Tun and Wingfield (1995) gave older people (60–91 years) a questionnaire asking about experiences of difficulty carrying out different kinds of dual-task activity in everyday life, such as walking while doing housework. Reported difficulty increased with age, particularly for activities in which a sustained attention task had to be combined with another task, such as looking for a sign while driving. Unfortunately, there was no direct test of actual performance. Tun and Wingfield suggested that the self-ratings reflected participants’ confidence in their ability to perform these tasks. Some research on self-report of age-related changes in cognitive function has found that there is a peak of complaints in the 50s. People in their 60s and beyond, who one would expect to have more problems, paradoxically report fewer difficulties in their everyday absent-mindedness and memory lapses (Rabbitt and Abson, 1990). Rabbitt and Abson suggested that this is because the older old have fewer
comparisons with the young and fewer opportunities for observing discrepancies between self-assessed and actual levels of competence. In addition, they may be making comparative judgements against their own performance in the remembered past, or with their beliefs about the capabilities of their contemporaries. In general, people can only make a relative judgement. Furthermore, information processing declines may make older people less able to monitor performance, less aware of mistakes, and less able to remember making them (Rabbitt, 1990).
Rabbitt et al. (1995) investigated the validity of older people’s self-reports. They were particularly concerned with questionnaires designed to assess cognitive problems, such as the Cognitive Failures Questionnaire (CFQ). They concluded, having reviewed several reports showing moderate correlations between CFQ scores and measures of depression, that in fact CFQ scores reflected a mixture of effects. They speculated, consistent with a view attributed to Donald Broadbent, that poor CFQ responses were to a degree determined by feelings resulting from depression. According to this view, depression also directly affects cognitive performance, possibly because of its effect on selective attention. Thus, older people report cognitive difficulties because of feelings of depression rather than direct awareness of cognitive difficulties, but the reports may be valid because the depression also impairs cognition.
6.4
Summary
Changes that are obvious and have a transparent link with performance are more likely to be acted on appropriately. Explicit feedback from a professional, such as an eye specialist, prompts behaviour change in this way. Some adjustment to behaviour may occur without conscious awareness, there being some evidence for this in relation to the patterning of complex motor skills and driving style, and possibly in relation to night time travel. In general, older people say that they cut back on driving because of problems with vision, other health problems, discomfort, and loss of confidence (Lyman et al., 2001). However, even when the changes they do make should at face value reduce accident risk, there is little firm evidence that they are effective in doing so. Indeed, some changes in road-crossing strategy, such as taking a two-lane road one lane at a time, may increase the risk of an accident. Older people may not notice their own cognitive impairment, and evidence from research on driving accidents implies that older people with cognitive impairment are often victims.
According to the SOC model, age-related performance decrement results when the capacity to compensate is exhausted, and this capacity itself declines with age (Baltes and Baltes, 1990). The SOC model also emphasises the variability of
individual older people’s capacity to compensate, and the need, therefore, to provide support that is tuned to their differing needs. Indeed, even if older pedestrians did manage to compensate for functional impairment fully, and maintained the low accident rate of middle-aged pedestrians, they would still experience more fatalities and serious injuries because of their increasing fragility. We discuss intervention in the next section. Some key points from this section are:
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Research suggests that older people’s beliefs about impaired abilities can be accurate when they have good environmental feedback. However, for cognitive changes especially, the evidence is that awareness of impairment is poor in many cases.•
Older people are relatively unlikely to have good insight into the abilities, particularly attentional and cognitive skills, most relevant to accident risk.•
Although older people do try to compensate for difficulties, there is no clear evidence that they successfully reduce accident risk.•
Some compensatory mechanisms operate without conscious awareness, and so would not in theory require executive resources. However, there is evidence that even tasks like walking absorb more of the available cognitive resources than in younger adults. Because of this, and a reduction in executive resources in older people, ability to compensate in acute situations is compromised.•
Specific high-risk groups would be expected to be particularly affected on theoretical grounds. Older people with abnormal cognitive impairment will have reduced insight into their own difficulties, compromising their ability tocompensate. Also, slow walkers may be relying more heavily on cognitive resources to maintain balance, negotiate obstacles, and so on, reducing the availability of resources for compensation.
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Older people have been shown to be able to prioritise resources to optimise performance on key tasks such as balance. Nevertheless, for many older old people, capacity for compensation through planning or cognitive effort reduces at the same time as increasing functional decline creates greater demand for attentional control.6.5
Research implications
It may be that drivers are more aware of impairment because the driving task provides clear feedback on performance difficulties. It would be useful to know whether the level of awareness differs between drivers and non-drivers.
Researchers have hypothesised that older people may not be aware of functional problems because they are less able to process or remember the errors or other sources of feedback that would create this awareness. It would be useful to have direct evidence for this. Similarly, evidence is lacking on the capacity of older people to make plans and strategic changes in response to information on functional impairment or road safety advice.
Further research is needed to evaluate the most effective sources of feedback found in the everyday environment, and to identify key skills for which good feedback is not usually available. Subsequently, interventions could be developed that help older people to gain awareness of these difficulties.
There is a complete lack of research on individual differences in relation to awareness of problems and decisions to modify behaviour. Lincoln and Radford (1999) pointed out that people with PD often give up driving voluntarily, but speculated that some may make over-conservative decisions, whereas others may
continue driving for too long. People are not all the same. To optimise the mobility of older people, it may be important to be able to characterise individual differences of this kind.
Little is known about the prevalence of cognitive impairment among older
pedestrian accident victims, although a good deal of work has been done on older drivers. Knowledge about these patterns is a prerequisite for identifying appropriate compensatory steps or other interventions.
An important area for further work is how older people respond to situations in which a rapid response to quickly changing circumstances becomes necessary. According to various accounts of cognitive ageing, the capacity to respond
effectively is probably poorer for older people. Some relevant studies were reviewed in section 2.4, but we lack a clear understanding of how people with physical
impairment and declining cognitive resources cope with crises. Keall (1995) also called for research on this issue.