A Cognitive Constraint Model of Dual-Task Trade-offs in a Highly Dynamic Driving Task

A Cognitive Constraint Model of
Dual-Task Trade-offs in a
Highly Dynamic Driving Task

Duncan Brumby
Andrew Howes
Dario Salvucci

Duncan Brumby, Drexel University | Brumby@cs.drexel.edu

questions to address ...

• why do people interleave tasks rather than
completing one task before moving to another?

• when in a task are people likely to switch?


scope of behavioral adaptations are
bound by constraints

• deprived of regular attention driving
performance rapidly declines with
potentially disastrous consequences

• ... but switching between tasks carries costs

• beneﬁts of frequently interleaving tasks play
against the costs of switching between them


overview of talk

• background
- the problem with doing more than one thing at once

• model
- a cognitive constraint model of distracted driving

• results
- a speed/accuracy trade-off

• conclusions


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

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

- driver distraction is a major contributing cause of trafﬁc accidents


what’s the cause of the problem?

• 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 potential bottlenecks


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)
for a 9-key task there are 28 (or 256) possible strategic variations!

when should one switch between
tasks?

• Payne, Duggan, & Neth (in press, JEP:General)

- moment-to-moment decision to switch is dependent on
characteristics of the current task

- found that task switching behavior is explained by optimal
foraging theory (Green, 1984; Stepthens & Krebs, 1986)

• people are sensitive to the task environment


in a highly dynamic driving task

• ... safety clearly matters

• a common surrogate measure is lateral
deviation of vehicle from lane center

• aim to develop a model that predicts changes
in lateral deviation under dual-task conditions


model of distracted driving

Task A: dialing
switch cost
Task B: steering
Lateral Deviation (m)

Con
verg
rge e
e
v
Di

Center of
road
Time (s)


parameterizing the model

• analyze human steering data to estimate
basic driving model parameters

• express trends in data as functions of time
and the vehicle's lateral deviation


steering episodes

• episodes are deﬁned as periods where the
angle of the steering wheel does not alter

• divergent steering episodes,
- when initial lateral deviation is less than at the end

• convergent steering episodes,
- when initial lateral deviation is greater than at the end


analysis of divergent steering episodes
Lateral Deviation = 0.2833 x Duration

with increasing time between steering updates,
deviation from lane center increases

analysis of convergent steering episodes
Lateral Velocity = 0.1756 x Lateral Deviation + 0.1034
d
where, v =
t

€

as the car gets further from the lane center,
velocity of correction to center increases

dial task (based on Salvucci, 2001, IJHCS)

• enter a 7-digit number
- (+ “power-on” and “send” key-presses = 9 key-presses in total)

• each key-press takes 310 ms
- 50 ms for recalling the digit

- 50 ms step of cognition, where the motor response is initiated

- 150 ms motor preparation and 60 ms motor execution for the key
press


dial task (based on Salvucci, 2001, IJHCS)

• have to move the hand to and from phone,
each taking 800 ms

• switch cost of 185 ms, representing movement
of eyes to and from phone, or vice versa


a systematic evaluation of the
strategy space

• every possible interleaving strategy was
evaluated, but also ...

• enumerated over durations of steering update
- updates 0.15 s to 1.5 s were explored at 0.15 s increments

- in total, 262,701 strategies evaluated

- each strategy was run 50 times and performance averaged

• interest in lateral deviation and dial task time


results: a speed/accuracy trade-off

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



xxxxxxxxx

FA = Fastest
SF = safest



x-x-x-x-x-x-x-x-x
vs.
x-x-x-x-x-x-x-xx

FA = Fastest
SF = safest



x-xxx-xxxx-x

FA = Fastest
SF = safest



x-xxx-xx-xx-x

FA = Fastest
SF = safest


summary

• analysis explored implications of constraints
from environment and on cognition for behavior

• given these constraints, we analyzed the speed
and safety of the set of possible strategies


summary

• allows full evaluation of strategy space

• derive predictions of performance brackets
- fastest possible and slowest reasonable (c.f. Kieras & Meyer, 2000)

• rather than using model to ﬁt data, we can
explain why people prefer one strategy over
another, in terms of speed/accuracy trade-off


A Cognitive Constraint Model of Dual-Task Trade-offs in a Highly Dynamic Driving Task

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A Cognitive Constraint Model of Dual-Task Trade-offs in a Highly Dynamic Driving Task