Document Type



A major handicap for studies of perceptual time on the highway has been the lack of an adequate means of simultaneously starting a chronoscope and exposing a highway situation to a subject. The problem is better appreciated when it is realized that on the one hand the subject's vision must be restricted from the situation to be exposed. On the other hand he must be permitted to view the road for a certain distance ahead of the car. The latter is necessary to allow for adjustment of the eyes to the existing level of illumination and for adaptation of the eyes to a distant point of fixation. Two methods for measuring perception and judgment time on the highway were proposed by Forbes (1939). He was concerned with the problem of determining the time required for making a decision to pass a vehicle ahead after rounding a curve. One method was to have a person other than the driver start a timer when he felt that first clear vision was possible after negotiating a curve. The timer was stopped by the sudden depression of the accelerator which was considered as an indication of the decision to pass. The second method was to take aerial photographs of the same situation. The time was determined from the number of frames taken between a point marking the spot where first clear vision was possible and where the vehicle started to move into the other lane to pass. As these methods are quite restricted in their use it has been the purpose of the writer to design an apparatus which could be used in a variety of situations.

Publication Date


Journal Title

Proceedings of the Iowa Academy of Science





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©1950 Iowa Academy of Science, Inc.



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