1. Issues in measuring sensory-motor control performance of human drivers: The case of cognitive load and steering control Johan Engström, Volvo Technology Corporation European Workshop on Advanced Predictive Sensory-motor Control Joudkrante, Lithuania,

2. Vehicle & Load Structures
Outline
Multitasking in the vehicle
Secondary tasks – visual and cognitive
The primary driving task – visual control of steering
Effects of secondary tasks on steering control
Different effects of visual and cognitive tasks
The ”lane keeping improvement” effect of cognitive load
Possible explanation in terms of satisficing vs. optimising steering control
Testing predictions implied by this hypothesis
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3. Multitasking in the vehicle: Driving + secondary tasks
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4. Secondary tasks: Visual vs. cognitive distraction
Visual distraction
Looking off road
E.g. Visual time sharing when tuning the radio
Cognitive distraction:
Engaging in demanding cognitive (working memory) tasks
E.g. Mobile phone conversation
Most real-world tasks involve both components…
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5. The primary driving task: Sensory-motor control in steering
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6. The visual control of steering: Optical and retinal flow
Wann and Wilke (2000)
Straight driving,
looking ahead
Straight driving,
looking to the left side
Retinal flow not equal to optical flow
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7. Using retinal flow patterns to guide steering: Look where you’re going
resulting heading
initial heading
Wann and Wilke (2000)
Underrsteering
Going towards target
Oversteering
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8. Gaze angle can be used as a direct cue for steering through curves (Land, 1998)
Fixate tangent point and adjust
steering to keep
gaze angle constant
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9. Vehicle & Load Structures
Combining retinal flow patterns and gaze direction: ”Spring” model (Wann and Wilkie, 2000)
Stiffness
Angular
acceleration
Reliance on cues
Damping
Main point: Foveal vision is essential
for accurate steering!
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10. Effects of secondary tasks on steering control
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11. Effects of visual distraction on lateral control
Visual time sharing
Gaze angle
Looking away
Loosing visual input for steering control
Heading error builds up
Looking back
Large steering wheel correction
Speed reduction to compensate
Steering wheel
angle
Increased
lane
position
variance
Lane position
Speed
Engström and Markkula (2006)
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12. What about purely cognitive distraction?
Large number of simulator and real-world driving studies found reduced lane keeping variance during cognitive load (Brookhuis et al., 1991; Östlund et al., 2004; Jamson and Merat, 2005; Engström et al., 2005; Mattes, Föhl and Schindhelm, 2007; Merat and Jamson, 2008).
Engström, Johansson and Östlund (2005)
Does talking on the mobile
phone really improve
steering control?
SD lane position
Cognitive task difficulty
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13. Other effects of cognitive distraction: Gaze concentration
Victor, Harbluk and Engström (2005)
Normal driving
Cognitive task
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Other effects of cognitive distraction: Increased steering activity (number of steering reversals > 2 deg. per minute)
SW reversals/min
Engström et al. (2005)
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15. Summary: Effects of cognitive distraction related to lateral control
Improved lane keeping (!?)
Gaze concentration towards the road centre
Increased number of micro steering corrections (<2 deg)
How are these effects related? How can they be explained?
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16. Vehicle & Load Structures
Possible explanation
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Two key distinctions
Satisficing vs. Optimising
Top-down (endogenous) vs. Bottom-up (exogenous) attention selection
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18. 1. Satisficing vs. optimising
Target value
Comfort zone
Optimising: Minimising performance
error relative to a target state.
Satisficing: Maintaining performance
within acceptable boundaries.
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19. Example cost functions of optimising and satisficing in lane keeping
Lane position
Lane centre
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20. Example dynamics of satisficing and optimising
X_dot
Satisficing
Comfort
zone
Optimising X
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21. Vehicle & Load Structures
Simulations
Satisficing
Optimising
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22. 2. Bottom-up and top-down attention selection
attention bias
2. Bottom-up and top-down attention selection
Top-down
selection
Cognitive task
Other visual task
Vehicle
dynamics
Steering
Bottom-up
selection
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23. Vehicle & Load Structures
Top-down
attention bias
Normal driving
Steering easy and
automated task,
bottom-up-driven ->
satisficing
Top-down
selection
Other visual task
Vehicle
dynamics
Steering
Spare top-down
attentional resources used
for other visual tasks
Bottom-up
selection
visual
time
sharing
Lane keeping variance
Distributed gaze
Only intermittent steering
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24. Vehicle & Load Structures
Top-down
attention bias
Cognitive load
Top-down
selection
Top-down attention allocated
to cognitive task
Cognitive task
Other visual task
No top-down-initiation of
other visual tasks
Steering
Vehicle
dynamics
Gaze can be fully devoted
to steering (attracted
bottom-up)
Bottom-up
selection
Reduced lane keeping
variance
Gaze concentration
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Testable predictions
General: Improved lane keeping should only occur if the driver is satisficing in baseline condition
Specific predictions:
Improved lane keeping should not occur if the steering task is difficult (so that satisficing is not possible)
Improved lane keeping effect should not occur if the driver is motivated to optimise lane keeping
Support for prediction 1
Cognitive load has been demonstrated to impair performance on tracking tasks (Creem and Proffitt, 2001; Strayer and Drews. 2001).
These tasks could be expected to be more difficult and/or less automated than normal driving
Prediction 2: Tested experimentally…
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26. Instruction to optimise steering (baseline)
Top-down
attention bias
Top-down
selection
Top-down attention allocated
to steering task and cognitive task
Other visual task
Optimising steering
performance
Steering
Vehicle
dynamics
Bottom-up
selection
Reduced lane keeping
variance
Gaze concentration
Increased steering
wheel control input
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27. Testing prediction 2: Experimental design
Simulator study in fixed based simulator (at Saab Automobile, Trollhättan)
Cognitive task: Count backwards with 7
48 subjects, split in 4 groups:
Incentive for group 1 and 2: Two cinema tickets instead of one if meeting some (unspecified) lane keeping criterion
Instruction to keep in the middle of the lane
Yes No
Cognitive task
Group 1
Group 3
Group 2
Group 4
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Prediction
Lane keeping improvement effect of cognitive load should only occur when the driver is not motivated to optimise lane keeping = satisficing
Interaction between cognitive load and instruction to optimise
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29. Preliminary results: Lane keeping (HP-filtered SD Lane Position)
No cognitive task
Effect only for non-instructed subjects
Due to satisficing in baseline condition
Cognitive task
Instructed to
optimise lane keeping
No instruction
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30. Steering wheel reversal rate
Cognitive task
Same effect in both conditions
Cognitive load less efficient optimising:
more steering – same lane keeping
performance
No cognitive task
No instruction
Instructed to
optimise lane keeping
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Still to be analysed…
Eye movements
Speed change
Performance on cognitive task
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Discussion
Replicated earlier findings for non-instructed drivers:
Reduced lane keeping performance
Increased steering wheel activity
Predicted effect of instructions found -> improved lane keeping only for non-instructed drivers – due to satisficing in baseline condition
Cognitive load seems to induce less efficient steering while optimising (more effort in steering, same result on lane keeping)
Cognitive task does not really improve steering ability-> the effect rather reflects ”involuntary” improvement from ”sloppy” baseline driving
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General conclusions
Caution is needed when interpreting driving performance measurements – do we compare to a baseline with satisficing or optimising performance?
In this case, changing instructions and/or driving task difficulty may cancel or perhaps even reverse the effect of cognitive load
Implies re-interpretation of many existing studies on the effects of cell phone conversation on driving performance (e.g. Strayer and Drews, 2001)
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