5.1. Eye movement methodology
Eye movements were used as the main measure in the current thesis, and in a first section of the general discussion we already discussed some of the advantages and disadvantages of head mounted eye tracking methodology. However, studying gaze behaviour might not always be the best way to study visual information processing. The differences in visual behaviour between adults and children in current thesis are believed to be mainly the result of developing cognitive functions. It would therefore be interesting to test these functions together with perceptual and motor behaviour. Other experimental methods such as occlusion and distorted vision could also shed more light on how visual information is processed and used for steering control. The constraints model implies that different sources of information can serve different control mechanisms (compensatory vs. anticipatory). Recent tests that measured brain activity during simulated steering tasks confirmed these suggestions (Billington et al. 2013). Combining eye movement research with brain activity can shed further light on how visual information is processed into steering commands.
Furthermore, the use of eye movements as a measure always leaves some important questions unanswered. Since only foveal vision is measured, it is difficult to estimate to what extent participants made use of peripheral information. Studies have shown that peripheral vision is of great importance for locomotion, therefore the use of peripheral information in young and adult bicyclists should be further tested.
5.2. Isolated steering tasks
In the current thesis, the different steering tasks were isolated on purpose to limit the presence of distracting elements. Although the outdoor tests suggest that the visual behaviour described in the indoor tests is transferable to actual traffic situations, this was only tested for cycling on a straight cycling track, separated from other traffic. It would be interesting to test steering behaviour on a more complex route including winding roads, different surfaces, different environmental settings, etcetera.
Furthermore, as was mentioned before, the current thesis only focussed on the steering task. In actual traffic settings, this is only one of the many tasks that have to be dealt with. Nevertheless, the findings of current studies provide valuable insight in how visual behaviour in function of the steering task is constrained. Future research should combine this steering task with other tasks such as hazard perception, synchronizing with other traffic participants, in-vehicle technology tasks, etcetera.
General discussion
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5.3. Development of visual behaviour
The young participants in current studies ranged from 6 to 12 years old. Since the cognitive functions are still developing during this period, there might have been considerable differences among the children. The subdivision within the children made in paper 5, supports the idea that some children already showed more adult-like perceptual- motor behaviour than others. Unfortunately, the sample sizes were too small to divide them into smaller age groups. Furthermore, as was shown in the introduction, elder bicyclists are also overrepresented in accident statistics. Since information processing capacity declines after adulthood (Kail & Salthouse 1994) elder bicyclists might have similar problems with complex traffic situations as children. However, in contrast to children, elder bicyclists have a lot of traffic experience to rely upon. It seems therefore advisable for future research to focus on larger groups ranging from young learner cyclists to older experienced cyclists, and investigate the link between the development of the cognitive functions and perceptual- motor behaviour in traffic.
5.4. Personal factors affecting visual-motor behaviour
The current studies were the first to explore the role of visual behaviour in the steering control of bicyclists and might serve as reference values for future experiments involving learner and adult bicyclists. However, the results might have been confounded by some other factors than the imposed conditions and the differences in age.
The smaller bicycles used by the children not only led to lower cycling speeds, but also to a lower eye level for children. This evokes a slightly different view on the environment and could have contributed to the differences in visual behaviour. Among adults, a different saddle height could also have led to a different head inclination, and therefore to a different visual behaviour. To make the visual-motor experience the same for all participants, the experimental setting and bicycle size should be scaled to the participant’s height. Alternatively, experiments could be carried out in a bicycle simulator which could provide identical stimuli for both adults and children.
Zeuwts et al. (2014) showed that there is a correlation between the cycling skills and the
general motor competence of 9-year-old children, and suggested that BMI might be
negatively associated with the development of cycling skills in children. Moreover,
environmental and psychosocial factors have often been shown to determine the likelihood
of choosing the bicycle for transportation (de Geus et al. 2008; Ducheyne et al. 2014). It seems likely that these personal characteristics not only affect cycling experience and cycling skills, but in turn also the visual-motor behaviour during cycling.
Since both the adult and the young participants were convenience samples recruited from colleagues, friends, family and neighbouring schools, the subject sample was rather homogenic. Adults were recruited from the department of health and movement sciences. Their level of physical activity was therefore most likely higher than the average in Belgium.
185 Regarding the children, most of them were recruited from friends and family of employees at the university. It is therefore likely that this sample of participants was biased towards higher levels of socioeconomic status. These samples of participants might have had more cycling experience and/or better access to bicycle facilities than the average population, which in turn could have affected their visual-motor behaviour while cycling. Therefore, the selection bias of adults and children who participated in the current experiments might have biased the results. It is advisable to take these and other personal characteristics into account in future research.
General discussion
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