Showing papers by "Benoît G. Bardy published in 1989"
TL;DR: It is put forward that the method used by the subjects to obtain TC may have consisted of combining the running speed with the braking distance (TC = BD/S), which partly challenges the ecological optics hypothesis (Lee, 1980) that TC is obtained entirely on the basis of the target expansion rate on the retina.
Abstract: Summary.-The aim of this study was to determine whether the speed information collected at the peripheral retina is used to assess the time-to-collision (TO with a target. For this purpose, 12 male volunteers were asked to perform a braking task consisting of running up to an obstacle under three experimental conditions: normal vision, central vision (13O), and central vision + 4O restricted peripheral information, presented 50-54O off center. Analyses show that the greater peripheral information available, the later braking occurred. The idea is put forward that the method used by the subjects to obtain TC may have consisted of combining the running speed with the braking distance (TC = BD/S). This partly challenges the ecological optics hypothesis (Lee, 1980) that TC is obtained entirely on the basis of the target expansion rate on the retina. A motor skill such as initiating braking on reaching an obstacle requires predictive visual control. This seems at first sight mainly to involve evaluating the distance to the target-object (judging from everyday expressions such as "distance control," "to keep at a distance," or "to misjudge one's distance" . . .), but time is in fact the predominant factor. Various authors (2, 3, 5, 6) have reached the conclusion that the time-to-collision (TC) plays a decisive role in the control of this kind of action. TC has been defined as the time necessary for an observer moving at a constant speed to reach a specific point on his trajectory. One of the main questions concerns the nature of the visual cues used by a subject to assess TC. The first possible means, according to the ecological optics approach (4), is based on an optical variable tau (7): this is defined by the inverse of the expansion rate of a target on the retina as it is approached. TC can be directly obtained from the expansion rate of the target approached by the observer, according to the formula:
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