Automotive User Interfaces and Interactive Vehicular Applications

Design and Make Aware: Virtues and Limitations of
Designing for Natural Breakpoints in Multitasking Settings
ABSTRACT
Drivers are frequently observed interacting with in-car devices
despite the well-documented dangers and (financial) penalties of
such behavior. It is therefore useful to think about how to make
such in-car multitasking situations safer. In this position paper we
discuss how the consideration of “natural breakpoints” in tasks
can be useful. We discuss the virtues of designing for such
breakpoints, but also highlight limitations especially related to
people’s awareness of their performance.
Categories and Subject Descriptors
H.5.2 [Information Interfaces and Presentation] User
Interfaces: Theory and methods; H.1.2 [Information Systems]
User/Machine Systems: Human factors
General Terms
Performance, Design, Experimentation, Human Factors, Theory
Keywords
Natural Breakpoints; Performance Trade-offs, Multitasking
1. INTRODUCTION
In-car multitasking such as dialing while driving is observed
frequently [18], despite over twenty year of research that has
highlighted the dangers and despite legal bans [e.g., 7]. Given this
natural urge for people to multitask in the car, the research
community should consider ways to alleviate some of the
problems associated with it. In this position paper, we discuss how
designing in-car applications with “natural breakpoints” in mind
might be valuable, and what limitations to such an approach are.
2. NATURAL BREAKPOINTS
Multitasking requires people to divide their attention between
multiple tasks, such as between a phone conversation and control
of the car. Although sometimes users can perform tasks truly in
parallel, typically they can mostly focus on one task at a time as
cognitive, perceptual, and motor resources are limited ([20], see
also [17]). For example, in a driving situation the eyes cannot look
at both the road and at the display of the radio. Due to these
resource bottlenecks, multitasking often inherently requires
people to make a performance trade-off in when to dedicate a
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Copyright held by author(s)
AutomotiveUI'11, November 29-December 2, 2011, Salzburg, Austria
Adjunct Proceedings
Christian P. Janssen, Duncan P. Brumby
UCL Interaction Centre, University College London
Gower Street, London, WC1E 6BT, UK
c.janssen@ucl.ac.uk, brumby@cs.ucl.ac.uk
resource to a task [14, 15]. Dedicating a resource to a task can
improve performance on that task, but might be at the cost of
performance on another task. How do people make such tradeoffs?
That is, how do they decide when to switch their attention?
One factor that can guide this process is the task structure. Goal
directed tasks can often be decomposed in a hierarchical manner
[6] with higher level goals (e.g., making coffee) being
decomposed into subgoals (e.g., pouring water into the coffee
machine), which are decomposed into even smaller steps (e.g.,
opening a lid). Research has shown that in multitasking situations
people are likely to interleave at “natural breakpoints”, where one
subtask has been completed and the next subtask is still to
commence (e.g., [2, 16], for more discussion see [11, 12]).
2.1 Virtues
Interleaving at natural breakpoints compared to other positions in
the task hierarchy offers many advantages (see also [11, 12]).
First, switching attention after subtask completion avoids the need
to remember details (to aid future resumption) about the state at
which a task was abandoned [3]. This reduces mental workload
[2]. Second, this also avoids having to later retrieve this
information, which makes task resumption faster [1]. Third, when
a subtask is finished, resources are no longer needed for
completion of the subtask. These then become available for other
tasks, which avoids resource bottlenecks [20]. Fourth, interleaving
at natural breakpoints compared to other points can also be
explained because this can offer a speed-accuracy trade-off [4, 11,
12]. Here the time cost to switch between tasks (e.g., the time
needed to switch attention and to resume a task) is minimal, which
makes it less costly to switch here compared to at other points.
Given these benefits, it is worthwhile for designers of in-car
systems to consider where the natural breakpoints in their
products are. That is, it is useful to think about the task hierarchy.
Recent systems have done this, by considering natural breakpoints
in deciding when to provide users with system-driven
interruptions (e.g., when to provide an e-mail alert) [9].
2.2 Limitations
Unfortunately, there are limitations to the use of natural
breakpoints as a means to encourage task interleaving. In our lab
we conducted studies in which participants had to steer a
simulated vehicle while also performing secondary tasks
(typically, manually dialing a phone number). We found that
people’s use of natural breakpoints depended strongly on their
priorities. Drivers that set safe driving as their priority made use
of the natural breakpoints to interleave secondary tasks for driving
[4, 11, 12]. However, drivers that set fast completion of the
secondary task as their priority omitted interleaving that task for
driving completely [4], or interleaved only at some of the natural
breakpoints [11, 12]. This implies that designing tasks to