Describes an experiment investigating strategic variability in cell-phone dialing while driving. Results suggest that designing devices to facilitate bursts of interaction might help alleviate egregious effects of use while driving.
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An Empirical Investigation into Dual Task Trade-offs while Driving and Dialing
1. 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
2. acknowledgments
• Dan Markley and Mark Zuber
- hacking the TORCS software and hardware integration
• funding: National Science Foundation (NSF)
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com
3. 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
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com
4. 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?
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com
5. 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
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com
6. 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.
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com
7. 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)
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com
8. 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.
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com
9. 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
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com
10. 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?
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com
11. 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
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com
12. 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?
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com
13. 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.
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com
14. 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.
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com
15. task objective affects strategy
more likely to switch between chunks than within chunks (xxx-xxx-xxxx)
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com
16. 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
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com
17. 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
Duncan Brumby, UCL Interaction Centre | DBrumby@gmail.com