Association cortex has roles in sensory and motor function, but the link between these roles is unknown. MST neurons respond to visual and vestibular signals about the heading of self-movement. However, their role in behavior is unclear because they have been studied during fixation tasks that are unrelated to heading. We view MST as linking sensory processing to the active control of heading. We will test this view by studying interactions between heading control and the heading responses of MST neurons. This theoretical framework will be tested as three specific hypotheses related to active heading control: 1) We predict that MST's response to heading stimuli will be enhanced when those stimuli control behavior. These responses will show graded enhancements during gradual turning toward the desired heading. 3) The strongest effects will be seen when the animal uses those stimuli to actively control its heading. Our novel laboratory combines optic flow, object motion, and whole-body movement heading stimuli. All three Specific Aims use comparable delayed match-to-sample paradigms to test the behavioral significance of heading responses. We will examine several levels of neural organization: single neuron firing, the synchrony of multiple neuron firing, neural firing, neural population signals, and functional-anatomic relations. Our goal is to determine if MST neuronal response to heading stimuli are influenced by the use of those stimuli to actively control self-movement. This tests whether MST should be viewed as a passive sensory processor or as a link between heading sensation and heading control. The results will be relevant to the neural mechanisms underlying disorders of spatial orientation and to the common errors of heading control that cause accidents and endanger us all at enormous cost to society.