Distance estimation in the Mongolian gerbil: the role of dynamic depth cues

The role of dynamic depth cues in distance estimation was investigated in the Mongolian gerbil. Animals were trained to jump randomly varied distances on a jumping stand under both binocular and monocular conditions. Videotape analysis revealed that prior to jumping, the gerbils executed a series of vertical head movements, the amplitude and velocity of which were related to the gap distance and to each animal's accuracy. This suggested that the gerbils were employing motion parallax cues to judge distance. An inverse relation between the magnitude of forward movement and the frequency of vertical head movements suggested that loom cues were also being used to judge distance. This hypothesis received support from a second experiment in which forward movements were constrained by a short take-off platform. In this condition, frequency of vertical head movements increased, suggesting that a compensation had occurred for the loss of information from loom.