A Three‐Channel Model for Generating the Vestibulo‐Ocular Reflex in Each Eye

Coding head movement involves representing the head's velocity and axis of rota- tion. The neural representation can then be used to inform perceptual and motor pro- cesses. An important motor response to head movement is the compensatory eye movements evoked, one component of which is the vestibulo-ocular reflex (VOR). Historically a three-neuron arc has been described as the core of the neural mecha- nism underlying the generation of the VOR.1,2 Such a direct line between sensor (the canals) and effector (the eye muscles) implies independent processing of the geo- metric components of the three-dimensional VOR.3 A more flexible and robust rep- resentation of the movement involves an interactive process in which the activity coding movement in each direction is interpreted in the context of the activity of the others. Many sensory attributes are coded by the activity of a small set of channels,4 and the closely constrained three-dimensional movement of the head could be effi- ciently represented by such a system. Psychophysical methods have been developed to investigate channel systems among which is adaptation. After adapting the re- sponse to a particular stimulus, the effect on the responses to closely related stimuli can often reveal a channel-coding system.5,6 Here we use an adaptation technique to provide evidence for a three-channel model underlying the representation of head ro- tation and generating the vestibulo-ocular reflex of each eye. These channels are conceptually different from those proposed for coding head velocity ranges,7 as dis- cussed elsewhere.8