In previous eye-tracking studies, data validation has rarely been attempted. For example, no validation was reported in Vansteenkiste et al. (2014a) or Mantuano et al. (2017).
Vansteenkiste et al. (2017) distinguished differences in the visual behaviour of a sample of children and adults. For the adult group, validation of the results was carried out using previous study data (Vansteenkiste et al., 2014a), where a similar experiment and model were used to study adults’ visual behaviour when cycling on a low quality vs high-quality path. However, this was only mentioned in general terms and no quantitative comparison was provided.
In comparison, Boya et al. (2017) conducted a meta-analysis comparison with research by (Gegenfurtner et al., 2011) to validate their findings.
Further, to validate their results, Fotios et al. (2015b) compared the proportion of observations of two visual categories, path and person, that were found to be significant for pedestrians with the same categories of two previous studies (Davoudian and Raynham, 2012; Foulsham et al., 2011).
As discussed previously in this study, observing the path was suggested to be critical for cyclists. To determine whether the rates of dual and SCR fixations related to path category in current study are similar to the rates found by previous studies on eye-
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tracking and cycling (e.g.Vansteenkiste et al., 2014a; Mantuano et al., 2017), fixations identified within path category were extracted from the two previous studies’ results for approximate comparability, see Figure 5.15.
It is worth mentioning that the two comparable studies were carried during daytime only, so no after dark trials exist in those.
In Mantuano et al. (2017), the proportion of fixations toward path was estimated by summing fixation frequencies of categories involving participants fixating on the road surfaces such as intersections, crosswalks, and road surface adjacent to discontinued pavement. The resulting number was then divided by the total fixation frequencies of all reported categories to get path fixation proportion. The study reported results of two road segments distinguished by a major quality: whether the cycle path is shared with pedestrians or not. The study then concluded that cycling on a road shared with pedestrians causes more attention diversion and less fixation on elements related to cycling safety such as fixating on the path. The proportion of fixations toward path reported in Figure 5.15 corroborates this statement as more fixation toward path was found on the cycle path not shared with pedestrians, which was also referred to as ‘separate’ in Figure 5.15.
In Vansteenkiste et al. (2014a), cyclists' visual behaviour on high quality and low quality paths was compared. The former path is a renewed part of the road mainly paved with bricks where minimum deficiencies could be found, whereas the latter path comprised large tiles that either had shifted or were missing.
Fixations related to the path category found on the low quality path had a proportion of 0.63 from the total fixations, on the high quality path this proportion equalled 0.25. These proportions suggest that cyclists were keen to observe the path surface more while on the low quality path.
In the current study, the dual and SCR fixation rates under path category were almost similar to the ranges reported by previous studies. For the after dark trials, the proportion of fixations towards path were 0.54 and 0.47 for dual and SCR fixations, respectively. These proportions were lower during the daytime, 0.41 and 0.39 for dual and SCR fixations, respectively.
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Participants' inclination to observe the path more during the after dark is logically due to the lower visibility than that of daytime, another indication of the importance of light properties for safe cycling.
Figure 5. 15. Proportion of fixations classified under the path category in current and previous studies.
In Mantuano et al. (2017) ‘Shared’ refers to cycle path which is shared with pedestrians whereas ‘Separate’ indicates the path without pedestrians. In Vansteenkiste et al (2014a), HQ = high quality path, and HL= low quality path.
5.9 Summary
This chapter reported results of the eye-tracking experiment conducted in the real world context to determine important environmental elements that cyclists are more likely to observe. This was conducted to provide empirical evidence about where light should be provided for cyclists to increase safety levels.
One essential objective in the current study was to overcome limitations in previous eye-tracking studies where critical fixations, moments where participants paid genuine attention to what they are looking at, were not discriminated from the overall fixation data. Another aspect which the current study responded to was the literature lacking comprehensive eye-tracking studies on cycling in real world settings.
Through synchronisation with the fixations produced by the eye-tracking apparatus, critical moments identified by either the dual task or SCR methods yielded critical fixations which were denoted as dual fixations and SCR fixations according to each method.
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Analysis of the dual and SCR fixations suggested looking at the path is the most critical visual task while cycling. Participants fixated more on the path after dark than during the daytime, however, this was found to be significant in the dual fixations analysis only. It suggested a similar trend that was near significant in the SCR fixations analysis. Generally, dual and SCR fixations showed similar patterns in the target categories. This confirms the robustness of the findings in this study which were reached from two independent paths.
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