Article VI

Grahn, H., & Kujala, T. (2020). Impacts of touch screen size, user interface design, and subtask boundaries on in-car task's visual demand and driver distraction.

International Journal of Human-Computer Studies, 142, 102467.

In this article, we examined more deeply whether context-specific design can have a diminishing effect on visual distraction. Therefore, we set out to study how the interface’s interaction methods, in-car task’s subtask boundaries, as well as the size of a touch screen affect an in-car tasks’ visual demand and visual distraction potential using Kujala and Mäkelä’s (2015) testing method. The article consists of two experiments (N = 24 + N = 24) which results are considered both separately and jointly. In the experiments, participants conducted different tasks (e.g., searching a song, reading an email, writing an email) with the automotive-targeted application and with regular smartphone applications while driving in a simulator. The tasks conducted with the automotive-targeted application were executed utilizing speech-to-text and read-aloud functions together with button presses or with simple swiping gestures. The tasks conducted with smartphone applications were executed utilizing a touch screen keyboard or with button presses.

There are several contributions in this article. The overall result, analyzed with multilevel modeling, was that the context-specific design was able to diminish visual distraction: besides the lower distraction potential, tasks conducted with the automotive-targeted application had also lower visual demand than the tasks conducted with regular smartphone applications.

According to the multilevel modeling, the automotive-targeted application significantly decreased in-car glance durations compared to regular smartphone

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applications. We also noted that, perhaps against common belief, bigger screen size had only a minor effect on diminishing the duration of an in-car glance.

Based on this, we suggest that the interaction methods of the application are more crucial than merely, for instance, the size of the screen the tasks are conducted with. In addition, we concluded that the orientation of the screen had no effect on drivers’ visual distraction.

We also found a plausible impact of subtask boundaries on tested tasks’

visual demand and visual distraction. If a task could be divided into smaller subtasks that are determined at the user interface level, together with speech-to-text and read-aloud functions, this may decrease the task’s visual demand and drivers’ visual distraction.

In this article, we were also able to identify three task groups based on their visual demand: visually high demanding, visually intermediate, and visually low demanding tasks. All of these task groups have their own generalized features, which are presented in Table 1.

TABLE 1: Features of the task groups Features of visually high

demanding tasks Features of visually

intermediately demanding tasks

Features of visually low demanding tasks Touch screen typing,

self-selected subtask boundaries Speech-to text function, read-aloud function, subtask boundaries determined from the user interface

Simple swiping gestures

The findings above contribute to research question 3 (What are the effects of selected in-car task features on drivers’ visual distraction potential?): as an interaction method, speech-to-text and read-aloud functions seem to diminish the visual demand and distraction potential of the tested tasks compared to regular smartphone applications, well-designed subtask boundaries may decrease drivers’ visual distraction, and simple swiping gestures are visually low demanding for drivers.

In addition, with multilevel modeling, we were able to indicate that, overall, the context-specific user interface design is capable of diminishing in-car glance durations.

In addition, we suggest a dissociation between visual demand and visual distraction should be made. We justify this suggestion with the observation that some tasks required a high number of in-car glances to be completed – even though the measured visual distraction potential of the task was low. This indicates that the mean number of glances is not alone a sufficient metric for assessing in-car task’s visual demand or visual distraction since the visual demands of the driving situation have an impact on glance durations and how distractive the particular in-car glance is. Hence, even if increasing visual demand of the task (measured with total in-car glance durations or number of glances) may increase task’s visual distraction potential, visual demand of the task and visual distraction caused by the task are not inevitably congruent. This

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observation contributes to research question 2 (How can driver inattention be measured more reliably and with better validity?): driver inattention can be measured more reliably by taking into account the visual demands of the driving scenario.

In addition, to our best knowledge, this was the first study to analyze tasks’

visual demand while the variable situational demands of the driving scenario were controlled.

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The aim of this doctoral dissertation was to clarify the definition of attentive driving and to examine how to measure inattention more reliably and with better validity based on this definition. In addition, one aim was to better understand the effects of in-car tasks’ features (e.g., text input methods, subtask boundaries) on drivers’ visual inattention based on the operationalization presented in this dissertation. Therefore, initially three research questions were posited:

1) What is attentive driving?

2) How can driver inattention be measured more reliably and with better validity?

3) What are the effects of selected in-car task features on drivers’ visual inattention?

This chapter presents answers to these research questions. It also considers the theoretical, methodological, and practical contributions drawn from the included articles. The contributions are discussed reflecting the theoretical foundation.

4.1 Theoretical implications

4.1.1 Working definition of attentive driving

According to existing literature, there is no commonly agreed upon definition of driver inattention (e.g., Foley et al., 2013; Kircher & Ahlström, 2017). If we want to define driver inattention and when it occurs, we must first know what attentive driving is and how to define it. Hence, this dissertation’s first theoretical implication is a suggested working definition for attentive driving which could further facilitate the traffic safety research community to define driver inattention.

In Article I (Grahn et al., 2020), by studying the mental contents of experts while driving, we were able to identify situation-specific uncertainties that are related to safe (and economic and comfortable) driving. The uncertainties here refer to possible events regarding upcoming driving situations that may or may