Assisting the older driver - SWOV

Assisting the older driver
to respond as soon as they detected the red square by pressing a microswitch
that was attached to the index finger of their left hand. Reaction time was
measured in milliseconds. If a reaction time had not been detected within 2.5
s from the onset of the stimulus, this was coded as a missed signal. Series of
signals were presented during the approach and passing of a selected
number of intersections and while driving on three straight road sections.
The 28 selected intersections were representative for the total group of 71
intersections, at the same time preventing participants having to perform the
detection task at every intersection they passed. The onset of a series of
signals was announced with a bell tone. During the series of signals (one
series per intersection), on average every 3.5 s, with random variation
between 3 and 4 s, a stimulus was presented at a horizontal angle of 10 to 20
degrees to the left of the line between the eyes of the participant and the
centre of the screen. Stimuli were presented at a vertical angle of 3 degrees
above the horizon. Average reaction time and fraction of missed signals per
intersection (number of missed signals divided by total number of sent
signals while passing the relevant intersection) were used as workload
indices for the intersections. Higher reaction times and higher fractions of
missed signals were interpreted as being the result of a higher workload.
Baseline reaction times and fractions missed were collected at the start of the
first experimental drive. While the simulator car was parked at the beginning
of the route, and the participant was sitting in the driver seat, one series of
twenty stimuli was presented. On average every 4 s, with random variation
between 3 and 5 s, a stimulus was presented at a horizontal angle of 10 to 20
degrees to the left of the line between the eyes of the participant and the
centre of the screen. Again, participants were instructed to press the button
as soon as they saw the stimulus. A second baseline was provided by the
straight road sections at which the same series of stimuli were shown as
during the approach and passing of the selected number of intersections.
This second baseline differed from the first one in three ways: 1) participants
were driving, 2) it always took place during the same drive as in which the
relevant intersection data were gathered (same support condition), and 3) the
frequency at which the stimuli were presented was every 3.5 s instead of
every 4 s. Practise on the PDT was provided during the familiarization run.
Before any of the analyses with regard to workload (see Section 8.2.5) were
carried out, all average reaction times – those averaged per intersection as
well as those averaged per baseline – were first corrected for missing data.
Initially, average reaction times represented the average of the reaction times
164