the "place" code used by the SC into the "rate" code used by oculomotor neurons. Eye movements are generated by six muscles, arranged in three orthogonally-aligned pairs. Thus, at the level of the final common path, eye movements are encoded in essentially a Cartesian coordinate system. Although the SC receives a strong input directly from the retina, in primates it is largely under the control of the cerebral cortex, which contains several areas that are involved in determining eye movements. The frontal eye fields, a portion of the motor cortex, are involved in triggering intentional saccades, and an adjoining area, the supplementary eye fields, are involved in organizing groups of saccades into sequences. The parietal eye fields, farther back in the brain, are involved mainly in reflexive saccades, made in response to changes in the view. Recent evidence suggests that the primary visual cortex (V1) guides reflexive eye movements, according to V1 Saliency Hypothesis, using a bottom-up saliency map of the visual field generated in V1 from external visual inputs. The SC only receives visual inputs in its superficial layers, whereas the deeper layers of the colliculus receive also auditory and somatosensory inputs and are connected to many sensorimotor areas of the brain. The colliculus as a whole is thought to help orient the head and eyes toward something seen and heard. The superior colliculus also receives auditory information from the inferior colliculus. This auditory information is integrated with the visual information already present to produce the ventriloquism effect. Distractibility As well as being related to eye movements, the SC appears to have an important role to play in the circuitry underpinning distractibility. Heightened distractibility occurs in normal aging and is also a central feature in a number of medical conditions, including attention deficit hyperactivity disorder (ADHD). Research has shown that lesions to the SC in a number of species can result in heightened distractibility and, in humans, removing the inhibitory control on the SC from the pre-frontal cortex, therefore increasing activity in the area, also increases distractibility. Research in an animal model of ADHD, the spontaneously hypertensive rat, also shows altered collicular-dependent behaviours and physiology. Furthermore, amphetamine (a mainstay treatment for ADHD) also suppresses activity in the colliculus in healthy animals. Other animals Other mammals Primates It is usually accepted that the primate superior colliculus is unique among mammals, in that it does not contain a complete map of