VISUAL INFORMATION ABOUT TIME-TO-COLLISION BETWEEN 2 OBJECTS

In a forced-choice paradigm, human observers' sensitivity to visual in formation specifying a moving object's future time of arrival at a des ignated position in the field of view was evaluated. A geometrical ana lysis demonstrated that information specifying a first-order temporal relationship (i.e., without taking changes in velocity into account) i s available in the combination of the relative rate of dilation of the optical contour of the moving object and the relative rate of constri ction of the optical gap separating the moving object from the target position. Observers were sensitive to information contained in the rel ative rate of constriction of the optical gap if no contour dilation c omponent was present and to the combination of information contained i n the relative rates of dilation of the optical contour of the moving object and constriction of the optical gap if both were present albeit with a differential weighting of the 2 components.