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RESEARCH MATTERS
Attending to Attention
Yukio Akashi, Ph.D.
Lighting Research
Center, Rensselaer
Polytechnic
Institutete
CAN GOOD LIGHTING HELP
to reduce the number of traffic crashes
A survey conducted in the U.S.
reported that approximately 50 percent
of crashes were related to drivers’
improper attention (Treat et al.,
1979).We are fortunate that research
on attention flourished over the past
three decades (Johnson and Proctor,
2004). Findings from these studies
may bridge the gap between lighting
research and traffic safety.
What Makes A Driver
Inattentive
Driving is a demanding, multitasking
activity.A driver has to maintain a
vehicle within a traffic lane while
keeping its speed below (or at least
not too far above) the limit, while following
other vehicles (referred to as
a “tracking task” in this column).
Occasionally, a driver has to pass
other vehicles and change lanes (a
“changing task”).Talking on a cellular
phone is an additional, but unrelated,
task that increases the driver’s task
load (a “distracting task”).
On less frequent but more critical
occasions, the driver must quickly
detect oncoming traffic and obstacles
such as torn tires on the pavement or
deer on the shoulder, to avoid collisions
with these potential hazards (a
“detecting task”).
As task load increases, a driver,
who is already busy driving and talking
on a cellular phone, can become
distracted from such detection tasks.
Inattention often originates from high
task loads, and often results in missing
targets and prolonged reaction times
(Verwey, 1993), and even increased
crash rates (Harms, 1986).
How Does Task Load
Affect Performance
For each task described above, a
driver must deal with a sequence of
three distinctive information-processing
stages: perceptional analysis (stimulus
identification); response selection
(decision-making);and motor response
(response execution) (Pashler, 1998;
Johnson and Proctor, 2004).
As Figure 1 illustrates, these
stages are often assumed to occur
sequentially, so the results of one
stage form the input to the next
stage. Of these, response selection
(decision-making) is the most
demanding stage for the brain. This
stage limits allocation of attention
resources that can be shared with the
other tasks, and it often appears to
act as a bottleneck (Welford, 1952).
To explore the mechanisms of
dual-task performance, scientists use
a sophisticated experimental technique.
This technique has a subject
respond to two individual stimuli, in
which the time between the first and
second stimulus varies in order to
change task load.This method helped
scientists conclude that the time it
takes to respond to the second stimulus
generally becomes longer (due
to the period of slack in Figure 1)
than when the second stimulus is presented
alone or the task becomes
more demanding (Vince, 1949).This is
because the decision-making stage of
the second stimulus cannot begin
until the corresponding stage of the
first stimulus has been completed
(Pashler, 1998). However, scientists
have also noted that the decisionmaking
stage of the first stimulus can
share attention resources with that of
the second stimulus when both tasks
are very difficult (Navon and Miller,
2002). In these cases, a kind of interference
occurs,and the decision-making
of the first stimulus is often
slowed down as well.
How Can Good Lighting
Improve Driving
Performance
The information processing framework
described above allows us to
understand the effect of good lighting
F I G U R E 1
Information processing framework (after Johnson and Proctor, 2004).
on driving performance. To this end,
this column reviews recent studies in
which subjects performed detection
tests (Task 2 in Figure 1) while
engaged in simulated tracking and real
driving tasks (Task 1). These studies
compared performance under metal
halide (MH) and high-pressure sodium
(HPS) lighting at mesopic levels.
To investigate the mechanisms of
interference of lighting conditions
with task load and performance, a
study simulated a typical driving situation
by combining three tasks: a
tracking task, a distracting task and a
detecting task (Akashi and Neches,
2003). The tracking task required a
subject to keep a needle in the center
between a pair of thin horizontal lines
by rotating a control knob. For the
distracting task, the subject attempted
to complete verbal mathematical
(multiplication) problems as quickly
as possible. The detecting task
required subjects to signal immediately
upon detecting one of eight target
presentations.This study changed
task load by changing combinations of
the tracking and distracting tasks.
Figure 2 depicts the results of
these tests, which generally suggest
the following: as task load increases,
reaction time is increased; and target
detection under MH was better than
under HPS. These tendencies were
confirmed by statistical analysis.
Regarding interference, the tracking
task appears to just add the same
period of time to the baseline reaction
times (in the detection-taskalone
conditions) for both MH and
HPS lighting. This suggests that the
tracking task interferes little with the
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