An Empirical Investigation into Dual Task Trade-offs while Driving and Dialing

An Empirical Investigation into
Dual Task Trade-offs while
Driving and Dialing

Duncan Brumby
University College London

Dario Salvucci
Drexel University

Andrew Howes
University of Manchester
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com

acknowledgments

• Dan Markley and Mark Zuber
- hacking the TORCS software and hardware integration

• funding: National Science Foundation (NSF)


the problem of doing more than one
thing at once

• people frequently use a mobile device while
doing something else ...
- we listen to our iPod while walking through the city

- we use a cell phone while we are driving a car

• there is clearly a problem with doing this ...
- “iPod oblivion” lead New York to contemplate banning iPod use
on city streets (toptechnews.com, Feb. 2007)

- driver distraction is a major contributing cause of trafﬁc accidents


the problem of doing more than one
thing at once

• making use illegal does not work
- many countries have banned the use of handheld devices while
driving ... but people continue to use their phones

- in the UK 90% compliance with the introduction of ban in 2003
has since slipped to 75% compliance -- some 10 million drivers
(“careless talk”, news.bbc.co.uk, 2007)

• can we better design mobile devices for use
in dynamic multitasking environments?


approaches

• design heuristics
- Green’s 15-second rule: IF a task can be completed in less than
15-seconds, THEN it is safe for a driver to engage in that task

• empirical data
- people tend to dial in bursts of three or four digits at a time
before returning attention to primary driving task

• cognitive modeling
- used to better understand how people multitask


why interleave tasks?

• psychological constraints limit task parallelism
- To drive we have to look at the road

- ... to write a SMS text message we have to look at the phone,

- ... but the eyes have a limited ﬁeld of effective view,

- ... and this will lead to strategic choice.


how might limited resources be divided
between two or more continuous tasks?

• simple model
- at any given time task A or task B can be “active”

- model the information ﬂow between tasks

- assume that switching between tasks carries a time cost
(Allport, Styles, & Hsieh, 1994, Attention & Performance XV)

Task A
Switch Cost
Task B
Time (s)


explore permutations ...

Task A
Switch Cost
Task B
Time (s)

Task A
Switch Cost
Task B
Time (s)
as an upper bound there are some 28 = 256
possible ways to enter 9 key-presses while driving.

speed/accuracy trade-off
(Brumby et al., 2007, CHI)
strategy space shows
average performance
for each of some
263,000 modeled
strategies

KEY: FA = Fastest
C1F = fastest 3-4 chunking
C2F = fastest 3-2-2 chunking
C1S = safest 3-4 chunking
C2S = safest 3-2-2 chunking
SF = safest


the question at hand ...

• previous studies have focused exclusively on
demonstrating deleterious effects of distraction

• no attempt to understand possible strategic
variability in behavior

• we designed an experiment to investigate
dual-task trade-offs

• question: does task objective affect behavior?


experiment: main points

• 8 participants

• dialing task on a clam-shell phone
- repeatedly enter same 10-digit number: highly practiced

- encouraged to dial as quickly as possible -- feedback given

- errors had to be corrected; built-in speed/accuracy trade-off

• driving task in a simulator
- drive as close to the lane center as possible -- feedback given

- control steering only; no acceleration or brake

experiment: main points

• driving speed manipulated: fast vs. slow

• task objective manipulated: dialing vs. driving

- participants instructed to focus on dialing as quickly as possible or
on steering as safely as possible (within-subjects design, counter-
balanced)

- feedback given only on focus variable at end of trial

• question: how does task objective affect dial-
time and lateral deviation?


results: dial time

• single-task dial time is
equivalent to dual-task
dial time in the focus-on-
dialing condition.

• but dial time is greater
when focusing on steering
in dual-task conditions.


results: lateral
deviation

• single-task lateral deviation is equivalent to dual-task lateral
deviation in the focus-on-steering condition

• at faster driving speeds, lateral deviation is greater when focusing
on dialing in dual-task conditions.


task objective affects strategy
more likely to switch between chunks than within chunks (xxx-xxx-xxxx)


summary of ﬁndings

• people can adjust their multitasking strategy
dependent on task objectives

• strategy choice has consequences for
performance: cannot both dial quickly and
drive safely

• safer to take the time to make frequent
glances back to the road, even when the
secondary task takes only 5 seconds


implications

• total time distracted is less important than
extent to which driver makes frequent
glances back to the road ...

• therefore, design mobile devices to facilitate
short bursts of interaction

• more generally: people will use mobile
devices while engaging in other important
tasks, design ought to support multitasking

An Empirical Investigation into Dual Task Trade-offs while Driving and Dialing

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An Empirical Investigation into Dual Task Trade-offs while Driving and Dialing