Judging the time to collision with a simulated textured object: Effect of mismatching rate of expansion of object size and of texture element size

We measured the accuracy with which subjects estimated the time to collision with a simulated textured object approaching at constant speed along the line of sight. The independent variable was the ratioR, whereR = (rate of dilation of the texture elements that covered the simulated object) / (rate of dilation of object size). When matching was perfect (i.e.,R = 1.0), the mean of 12 settings was close to the nominal value of 2,000 msec for both subjects. In addition, the standard error of 12 settings was only 25 and 52 msec in 2,000 msec for the 2 subjects. Discrimination threshold for time to collision was not significantly affected byR over the range investigated betweenR = 0 andR = 2.0. However, the accuracy of estimating time to collision was significantly affected byR. Estimated time to collision was a monotonic function ofR. For example, when the mismatch was only 10% (i.e.,R = 0.9) subjects judged time to collision would occur 178 msec later than the true time to collision of 2,000 msec.