This paper reviews some attempts that exploit a phenomenon, also known as motion parallax, to estimate the distance of closest approach of a moving object. Despite their success, the existing methods lack some desirable properties, such as reasonable scalability and online learning. To overcomethese practically-relevantlimitations, this paper proposes a new model that is based on Hebbian learning. Due to its scalability and online learning capabilities, this model is especially suited to mobile robots. KEY WORDS Intelligent Agents, Robotics, Computer Vision