The role of image size and retinal motion in the computation of absolute distance by the Mongolian gerbil (Meriones unguiculatus).

In a series of experiments in which Mongolian gerbils were trained to jump over a variable gap, it was demonstrated that computation of the distance to be jumped was dependent on both image size and retinal motion, the latter cue being generated by the production of vertical translation movements of the head (head bobs). When image size was not a reliable cue, the animals produced more head bobs, thereby increasing the availability of retinal motion cues. The performance of the gerbils on various probe trials strongly suggested that they computed absolute distance by combining information about the velocity (or amplitude) of their head bobs with information about the velocity (or displacement) of the moving image of the landing platform.