Automobile accidents among older adults may be related to difficulties in judging the speed of other vehicles. To examine this possibility, 3 groups of observers in the young adult, middle-aged, and older adult age ranges were asked to estimate the velocity o fan isolated automobile traveling at 15-50 mph (24-80 kph). Across all age groups, perceived and actual velocity were related by a power function with an exponent of 1.36. Age was significantly and positively correlated with intercepts, but negatively correlated with exponents; that is, older observers showed less sensitivity to changes in actual velocity. Results bear on the issues ofontogenetic changes in accident involvement and sensitivity to motion.Although nonvisual factors play a role in effective driving performance, driving is predominantly a visual task. Hills (1980) estimated that more than 90% of the information impinging on the driver is visual in nature. Among the many visual tasks required by the driver, estimating the velocity of other vehicles appears to be one of the more salient. Velocity estimation plays a role in various traffic maneuvers, including intersection crossing, merging, and overtaking. Underestimations of vehicle velocity may place drivers attempting these maneuvers at greater risk of accident involvement. This may be particularly true for older persons, in whom a disproportionate number of both pedestrian and driver accidents may involve errors of velocity estimation (Faulkner, 1975; Hills & Johnson, cited in Hills, 1980;Sheppard & Pattinson, 1986). The data reported in this article were gathered to determine whether the ability to estimate vehicle velocity changes systematically over the adult life span. Speed Estimation and ScalingThe manner in which human observers process velocity information remains unclear, but evidence suggests that such information is used to make decisions about some driving maneuvers. For example, increasing traffic velocity leads to reductions in the minimum time gaps allowed when crossing against traffic flow (Bottom & Ashworth, 1978). Velocity estimation is often inaccurate, however. Many drivers err in estimating the last moment to safely overtake a vehicle in the presence of oncoming traffic (Jones & Heimstra, 1964;Kaukinen, 1972), and at This research was supported by a grant from the National Institute on Aging (AG-00110-02).We thank the Pennsylvania Transportation Institute for the use of their test track; the Oneonta, New York, Police Department for the use of their radar unit; and especially Joyce A. Blake-Guzy for her invaluable assistance in data collection.Lawrence T. Guzy is now at the State University of New York at Oneonta.Correspondence concerning this article should be addressed to Charles T. Scialfa, who is now at the Department o fPsychology, University of Calgary, Calgary, Alberta, Canada T2N 1N4. 60 least some authors (Leibowitz, 1985;Mackie, 1972) have argued that overtaking accidents are due in part to misjudgments of the oncoming vehicle's velocity. Such an argument raises...
Subjects compared the apparent repetition rates of trains of dichotically alternating clicks, presented at 1–40/sec, with the apparent rates of monotic trains. All dichotic rates were underestimated, the degree of underestimation varying from a few percent at 1/sec to 35%–40% from about 7.5/sec onward. The latter rate corresponds to the switching rates producing minimal intelligibility of speech presented alternately to the two ears. Unlike the results of switched-speech experiments, however, the present results appear to be unequivocally interpretable as indicating a difficulty in integrating dichotically alternating inputs into a single percept.
Examples of the inaccessibility of mental processes by means of verbal recall are described with particular reference to the accuracy of quantitative estimates of size, distance, and duration. Evidence is presented in support of the hypothesis that nonverbal retrieval techniques are more accurate than quantitative verbal estimates. Implications for the judicial process are considered.
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