Investigates how people adapt their multitasking strategies to varying performance objectives. Augments our understanding of how cognitive constraints limit dual-task strategy adaptations in complex dynamic environments.

1. Focus on Driving: How Cognitive Constraints Shape
the Adaptation of Strategy when Dialing while Driving
Duncan Brumby, University College London
Dario Salvucci, Drexel University
Andrew Howes, University of Manchester

2. DIALING
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average dial time 4.67 seconds
how to dial and drive?

3. QUESTIONS
• is it safer to dial quickly or slowly?
• how do people adapt their strategy to drive safely?

4. OVERVIEW
• framework for understanding multitasking
• well-controlled study that investigates the effect
of relative task priority on strategy adaptation
• use a model to ask what if ...

5. STRATEGIC CHOICE
• there are potentially many interleaving strategies
• choice of strategy affects performance and
impacts safety

6. SIMPLE MODEL
OF TASK SWITCHING
Task A
Switch Cost
Task B
Time (s)
• at any given time task A or task B can be “active”
• model the information flow between tasks
• switching between tasks carries a time cost
- i.e., shifting visual attention, recalling previous goal state
information, etc

7. PERMUTATIONS
Task A
Switch Cost
Task B
Time (s)
Task A
Switch Cost
Task B
Time (s)

8. DRIVER DISTRACTION
FRAMEWORK

9. STRATEGIC CHOICE
• there are potentially many interleaving strategies
• choice of strategy affects performance and
impacts safety

10. DECISION RULES
• planned: switch at subtasks boundaries (Salvucci, 2005)
• reactive: switch when the car veers

11. PREVIOUS WORK
• Horrey et al. (2004): behavior and performance
dependent on relative task priority
• resource allocation function: safer driving with
more time looking at the road than at a phone

12. STUDY
• how do people adapt their strategy for interleaving
dialing and driving to different objectives?
• objectives can be influenced by many things ...
- dial quickly, minimize perceived risks, conform to social
expectations, etc

13. DIALING TASK
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dial as quickly as possible
very few errors (4/160)
average dial time 4.67 seconds
70 ms pause between chunks, t(7)=2.58, p=.04

14. stay close to lane center
drive for 10-seconds, controlling only steering
less stable at faster driving speed, t(7)=5.40, p<.01

15. !quot;#$%&#$'()*

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18. LATERAL DEVIATION AT
KEYPRESSES

19. LATERAL DEVIATION AT
KEYPRESSES

20. INTER-KEYPRESS INTERVALS

21. CHANGE IN LATERAL ERROR IN
BETWEEN KEYPRESSES

22. COGNITIVE CONSTRAINTS LIMIT
STRATEGY ADAPTATION
• the only improvement in lane keeping came during
prolonged delays in between chunks
• even when extreme vehicle drift implies a more
reactive strategy could be safer

23. CONCLUSIONS
• interleaving intricately shaped by the structure of
the secondary task
• drivers steer at chunk boundaries

24. OUTSTANDING QUESTION
• data show what strategies were adopted
• cannot infer how alternative strategies would fair
• is there a more efficient strategy?

25. MODELING FRAMEWORK

26. STEERING CONTROL
• model parameters estimated from steering data
• data segmented into steering episodes
• periods where the steering wheel was not adjusted
• focus on relationship between lateral deviation at
the start of an episode and vehicle heading

27. DATA

28. DRIFTING
• discrete steering updates alter vehicle heading
• in between steering updates the vehicle drifts

29. FOCUS-ON-DIALING: DATA
• drivers did not interleave while dialing
Drift rate at slow speed Drift rate at fast speed

30. FOCUS-ON-DIALING: MODEL
• no-interleaving strategy used to fit drift rate at
different driving speeds
Drift rate at slow speed Drift rate at fast speed

31. QUESTION
• with drift rate across conditions fit ...
• how do various interleaving strategies perform?

32. STRATEGIES TO EVALUATE
S2 S5
xxx -- xxxxxxx xxx -- xxx -- xx -- xx
S3 S6
xxxxxx -- xxxx xx -- xx -- xx -- xx -- xx
S4 S7
xxx -- xxx -- xxxx x -- x -- x -- x -- x -- x ...

33. STRATEGY PERFORMANCE

34. STRATEGY PERFORMANCE

35. STRATEGY PERFORMANCE

36. INTERLEAVING AT CHUNKS
BOUNDARIES IS EFFICIENT

37. KEY INSIGHT:
WHEN QUICK IS SLOW
S1 No-interleaving
S4 xxx - xxx - xxxx

38. KEY INSIGHT:
WHEN QUICK IS SLOW
S1 No-interleaving
S4 xxx - xxx - xxxx

39. KEY INSIGHT:
WHEN QUICK IS SLOW
S1 No-interleaving
S4 xxx - xxx - xxxx

40. KEY INSIGHT:
WHEN QUICK IS SLOW
S1 No-interleaving
S4 xxx - xxx - xxxx

41. KEY INSIGHT:
WHEN QUICK IS SLOW
S1 No-interleaving
S4 xxx - xxx - xxxx

42. KEY INSIGHT:
WHEN QUICK IS SLOW
S1 No-interleaving
S4 xxx - xxx - xxxx

43. CONCLUSIONS
• drivers’ adapt their strategy to changing objective
• task interleaving strategy shaped by structure of
secondary dialing task
• it is safer to take the time to interleave even for
short tasks

44. FUTURE WORK
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45. FUTURE WORK
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46. ACKNOWLEDGMENTS
We thank our sponsors
• NSF
• EPSRC
• UCL Department of Psychology

47. UK DIALING