Each layer of the tectum contains a topographic map of the surrounding world. If neurons at a point in the map fire, it starts a response towards the corresponding point in space. In primates, the tectum ("superior colliculus") directs eye movements. Visual input from the retina, or "command" input from the cerebral cortex, create a "bump" of activity in the tectal map. If strong enough, this causes an eye movement. 