This paper examines the factors that most strongly affect drivers' judgment with regard to braking timing. Experiments were conducted with 7 participants on a test course. Participants in the trailing vehicle applied brakes according to their subjective judgments on how best to prevent a rear-end collision. Various factors such as following car speed, distance between two vehicles, relative velocity, time-to-collision (TTC), rate of change of visual angle (which is the inverse of TTC) and others were examined in discriminant analysis. It was revealed that the rate of change of visual angle, which is the inverse of TTC, is the most closely related to a driver's judgment of when to apply the brakes.

Dynamic temporal change in the size of functional visual field was measured using a dual task: a peripheral task in which one square in a background pattern of squares was changed in shape to a dot; and a central task involving the rapid serial visual presentation of a sequence of letters (RSVP task). The temporal lag between the occurrences of the dot and the RSVP target was manipulated. University students were asked to detect the dot and to depress a mouse button as quickly as possible while searching for the RSVP target among a sequence of distracter letters. The abrupt change in the shape of a background square in the peripheral task caused a processing deficit in the RSVP task at relative lags from -3 to -1 (255 ms to 85 ms before presentation of the RSVP target), but the encoding and retaining processes involved in identifying the RSVP target did not impair the detection of the peripheral dot. The functional visual field was found to expand while participants were performing the dual task, suggesting that preattentive detection is affected by general attentional activity.

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