Automotive User Interfaces and Interactive Vehicular Applications

2.1.6.3 Table Task
During the table task, a six-column table was presented with
alternating letter and number columns. The letters were associated
with radio call signs (e.g. A=alpha, B=beta, etc.). An auditory cue
was given with the call sign as the table was displayed. The task
was to search each letter column for the call sign letter and to
identify the digit to the right of it. Participants entered the three
digit code on a touch screen keypad. After entering the first digit,
the table disappeared, requiring the driver to memorize the 3-digit
sequence before entering their response. The assignment of digits
to letters and the order of letter and number presentations in the
table were randomly generated for each presentation. See Figure 2
for an illustration of this task.
A 1 B 1 E 1
T 3 T 2 Z 3
C 6 Z 6 B 6
D 4 D 5 F 4
B 9 A 9 C 9
E 2 F 4 A 2
F 8 E 3 D 8
Z 5 C 7 T 5
Figure 2. Table Task
Highlight
Request
response
Figure 1: Dots for Short and Long Glance Tasks
2.2 Experimental Design
There was one independent variable in this experiment: driving
condition. This variable had four levels: All participants drove the
test course 1) without performing a distracting secondary task, 2)
while performing the short glance task, 3) while performing the
long-glance task, and 4) while performing the table task. The
former condition served as a baseline performance measure and
the latter three served as treatment conditions. The resulting
design was completely within-subjects.
Several dependent measures were collected. Firstly, participants’
reaction time and accuracy on the distraction task and the
simulated braking task were collected. Reaction time was
measured from the beginning of each task. Accuracy was defined
as the percentage of correct trials.
Additionally, participants’ performance on the following driving
measures was collected: average speed, average number of
steering reversals, and average number of throttle reversals. All of
the aforementioned measures were sampled at a rate of 250ms and
averaged across trials. Speed was measured in mph. Steering
reversals were defined as the average number of deflections away
from a neutral steering position followed by a reversal of the
steering wheel back to the neutral position that were executed
within one second.[9] Similarly, throttle reversals were defined as
the average number of deflections of the throttle away from a
neutral point followed by a reversal of the throttle back to a
neutral position that were executed within one second. 8
2.3 Procedure
Before the experiment began, participants practiced the three
different distraction tasks in the stationary vehicle. Afterwards,
they were instructed to maintain a 20mph speed limit and drove
approximately one quarter of the course in order to gain
familiarity with the vehicle. Then, they practiced each of the
distraction tasks sequentially while driving.
After practice, participants were informed that their primary task
was to drive the vehicle safely and to complete any additional
tasks only when they felt that the driving conditions were safe
enough to do so. Participants executed four different driving
conditions: 1) a baseline condition, in which participants drove
without completing a distraction task, 2) a condition in which
participants completed the short-glance task, 3) a condition in
which participants completed the long-glance task, and 4) a
condition in which participants completed the table task. The
order of these conditions was counterbalanced across participants.
With the exception of the practice period, participants completed
only one type of distraction task type within a driving condition.
The experiment took approximately 3.5 hours to complete.
3. Results
All dependent measures were inspected for outliers using the z
score method.[6] Items receiving a score of + 3 were replaced
with the next highest or lowest score that was not considered an
outlier for that particular condition. Only 2.3 percent of the data
were replaced. By using this particular method, variance was not
unnecessarily reduced.[14]
3.1 Did participants perform as instructed?
Single sample t-tests were conducted to determine whether
accuracy on the secondary distracting tasks was significantly
different from chance. This was done in order to determine
whether participants were performing the task as instructed or
whether they were simply guessing (i.e., attaining a 50 percent
performance rate). As shown in Table 1, single-sample t-tests
revealed that participants performed significantly better than
chance on all three secondary tasks. This means that participants
were indeed performing the tasks as instructed.
Table 1. Percentage accuracy compared to chance on secondary
tasks
Task Mean SE Result
Short-glance 94.10 0.42 t(66) = 107.83, p < .001
Long-glance 84.59 1.08 t(66) = 31.89, p < .001
Table 96.26 .40 t(66) = 116, p < .001
3.2 Were participants significantly
distracted?
A one-way ANOVA was conducted in order to determine if
participants’ response times to the simulated brake light were
significantly different during the attentive driving condition
compared to each distracted driving condition. The results
indicated that participants responded significantly faster to the