Dick de Waard, PhD; Karel A. Brookhuis, PhD
de Waard D., Brookhuis K.; Drug Effects on Driving Performance. Ann Intern Med. 2000;133:656. doi: 10.7326/0003-4819-133-8-200010170-00021
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Published: Ann Intern Med. 2000;133(8):656.
TO THE EDITOR:
Weiler and colleagues (1) reported on results obtained by using a car-following task. We would like to comment on their use of this technique, which we had proposed in a previous article . In a car-following experiment, participants are requested to follow a lead car that varies its speed at regular intervals. The speed signals of the leading car and the following car are used as input measures, and results are analyzed in terms of three formally independent variables: 1) Coherence is a measure of squared correlation that indicates the accuracy of the driver's speed adaptations. A coherence of 1 is perfect and indicates that the two speed signals match exactly. 2) Modulus is the amplification factor between the two signals. This indicates the magnitude of overshoot in reaction. 3) From the phase shift between the speed signals, the delay in response can be estimated. This is the reaction time to the decelerations and accelerations of the lead car; it is the most important measure in a car-following experiment.
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