Detectability of relative motion as a function of exposure duration, angular separation, and background.

A signal detection design was used to measure detection thresholds for the motion of one spot of light relative to a stationary spot. Angular separations from 7.5' to 2°, exposure durations from .5 to 4 sec., and inward and outward motion were used with and without a textured background. An increase in angular separation lowered thresholds measured in minutes of arc per second. Increases in exposure duration lowered motion thresholds, but raised the total angular distance moved during exposure. Textured background had no effect. The results are related to previous findings and to following another automobile at night.