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

Duncan Brumby, Drexel University | [email protected]

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

Highly Dynamic Driving Task

Duncan BrumbyAndrew HowesDario Salvucci


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


• 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

doing more than one thing at once


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

Task BSwitch Cost

Time (s)


explore permutations ...

Task A

Task BSwitch Cost

Time (s)

Task A

Task BSwitch Cost

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

Task B: steeringswitch cost

Time (s)Late

ral D

evia

tion

(m)

Diverge

Converge

Center of road


• analyze human steering data to estimate basic driving model parameters

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

parameterizing the model


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 episodesLateral Deviation = 0.2833 x Duration

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


analysis of convergent steering episodes

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

€

v =dt

Lateral Velocity = 0.1756 x Lateral Deviation + 0.1034 where,


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 = FastestC1F = fastest 3-4 chunking

C2F = fastest 3-2-2 chunkingC1S = safest 3-4 chunking

C2S = safest 3-2-2 chunking SF = safest






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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

Education

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