A second important part of this thesis was to focus on the differences in visual and steering behaviour between experienced adult bicyclists and young learner bicyclists. All tests were carried out with both adults, and six to twelve year old children, except for the curvature steering test. In general, cycling speed of the children was lower than that of the adults. However, this is most likely largely due to the smaller bicycles that children used. Nevertheless, it is also possible that children adopted lower cycling speeds to compensate for their lower capabilities.
When cycling on narrow lanes (paper 3), children were not found to make more steering errors, and no general difference in visual behaviour was found either. Furthermore, with increasing lane width and cycling speed, children made the same shifts of visual gaze direction as the adults. For this simple precision steering task, children seemed to be able to adopt a similar visual-motor strategy as adults. When cycling in an actual traffic
environment (paper 7) however, children spent more time looking at the surrounding
environment and less to the path itself. Although children also made a shift of visual attention from the surrounding elements to the path region when cycling on a low quality path, they still paid more attention to the scenery, and less to the cycling path than the adults. This is in line with the findings of road crossing studies, that children fail to distinguish between relevant and irrelevant features, and fail to give priority to relevant features even when the task demands it (Foot et al. 1999; Whitebread & Neilson 2000).
During the slalom test, few distracting elements were present, and no difference in ‘task- irrelevant’ gaze was found between the adults and the children. Instead, the task demand was manipulated by making the slalom more difficult. Children made more errors as the slalom was more demanding, whereas none of the adults made any steering error. Since smaller bicycles are usually also more agile than large bicycles, the difference in number of steering errors is not likely to be due to the difference in bicycle size. Children were found to adopt a different visual behaviour, characterized by a focus on the upcoming cone, whereas adults looked at the functional space between the upcoming and the next cone. Furthermore, adults also tended to make more use of anticipatory fixations than children. These differences in visual behaviour suggested that children steered from one cone to another, while adults planned the their steering action ahead. From child to adult bicyclist, there seemed to be a gradual change from a simple and rigid visual-motor strategy, to a flexible, more holistic strategy to guide steering.
4.1. Constraints approach
The individual constraints were apparent when the visual behaviour of young and adult bicyclists were compared. Since the executive functions of 6 to 12 year old children are not mature yet (Schiebener et al. 2014; Best & Miller 2010), children have to adapt their perceptual-motor behaviour to their capabilities. The differences in visual behaviour between adults and children described in the current thesis, are most likely a reflection of
181 these cognitive constraints. Next to cognitive constraints however, children also have to deal with different physical constraints. Since children are smaller than adults, they use smaller bikes and have a lower eye level than adults.
In an actual traffic setting with many distracting stimuli, children seemed to be more distracted by task-irrelevant stimuli than adults. This suggests that children might be more susceptible for environmental constraints than adults. Surprisingly, the low quality road had a similar effect on both the visual behaviour of adults and children. However, the presence of distracting elements does not immediately affect the cycling task whereas the different road surface does. Correspondingly, manipulating the task constraints led to similar changes in gaze and steering behaviour in both adults and children.
In general, it seems that children’s visual behaviour changes in a similar way to changing
task constraints as the visual behaviour of adults. Due to the cognitive and physical constraints however, children have less attentional resources and apply it less efficiently.
4.2. The use of peripheral vision and gaze polling
Although there are no age differences in the detection of stimuli using peripheral vision (Cohen & Haith 1977), it has often been suggested that children make less use of their peripheral vision to guide their actions than adults (Franchak & Adolph 2010). In both paper 5 and 7 of the current thesis, it was suggested that children also might make less use of their peripheral vision than adults to guide steering. To compensate for a lack of peripheral information, making more and shorter fixations would be a logical solution. Unfortunately, since children have lower processing speeds, they are usually not yet able to efficiently make ‘quick checking fixations’ (Whitebread & Neilson 2000).
Peripheral vision and ‘gaze polling10’ have often been indicated as two important visual mechanisms for efficient steering (Wilkie et al. 2008; Crundall et al. 2002; Summala et al. 1996). If these two visual mechanisms indeed are lacking in children, this would be an important limitation in their visual information processing system regarding traffic behaviour. Unfortunately the use of peripheral vision to guide bicycle steering was not tested in the current thesis. Nevertheless, findings of paper 5 are in line with the suggestions that children make less use of short anticipatory fixation.
4.3. Visual behaviour of children and the current models for steering behaviour
The visual-motor behaviour of children is in line with in the constraints model proposed in the current thesis. It can be assumed that children’s information processing capacities11 are not mature yet (Chihak et al. 2010). Therefore, the total attentional resources12 of young
10
Also referred to as anticipatory fixations
11 The rate at which information can be efficiently processed 12
General discussion
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bicyclists is lower than that of adults. When task demand is low, such as in paper 3, this will hardly have any effects on the gaze and steering behaviour of children. In a more demanding task such as steering through a slalom however, the attentional resources of children are under pressure. Therefore, the children will not have the attentional resources to direct their attention to both compensatory (the first cone to be dealt with), and anticipatory information sources (the next cones). As a result, children will mainly focus on one task at the time, and disregard anticipatory information. Adults on the other hand, can divide their attention between compensatory and anticipatory cues more easily. In the slalom test this was achieved by using more anticipatory fixations, and probably also by using peripheral vision more efficiently. In line with the model, changes in the task demand had a similar effect on the need for anticipatory and compensatory information for both adults and children.
Since children fail to distinguish between relevant and irrelevant features, and fail to give priority to relevant features (Foot et al. 1999), the presence of distracting stimuli could be an additional problem for children. Whereas adults will look at task-irrelevant stimuli using spare attentional resources, children might look at task-irrelevant stimuli at the expense of compensatory and/or anticipatory information. Regarding the SEEV-model, children’s gaze behaviour might be guided more by bottom-up factors (Saliency and Effort), than by top- down factors (Expectancy and Value), compared to the adults. Due to these limitations in information acquisition and processing, valuable information might be missed, leading to a poor situation awareness. In turn, this could be the cause for the inappropriate gaze behaviour of young learner bicyclists.
4.4. Summary
The current experiments were the first to describe the visual control of bicycle steering in young learner bicyclists. The findings suggest that due their limited information processing capacities and attentional resources, children adopt a different visual behaviour while bicycling in a complex environment. Children were more easily distracted by task-irrelevant stimuli, and were less able to anticipate on future steering actions. However, similar to adults, children also adapted their visual behaviour to changing environmental and task constraints.
These findings suggest that in a more complex situation, the steering task is more demanding for children than for adults, and that children will cope with this by adopting a different gaze behaviour at the expense of anticipatory gaze behaviour. However, this might be at the expense of their situation awareness. In the current studies missing anticipatory information and having a poor situation awareness could only lead to steering next to a cone, at worst. If anticipatory clues would be missed in an actual traffic situation however, this could have far worse consequences.
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