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 ratio R, where R = (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 the 2 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 by R over the range investigated between R = 0 and R = 2.0. However, the accuracy of estimating time to collision was significantly affected by R. Estimated time to collision was a monotonic function of R. 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.