Fitting adaptation models to velocity step responses: simulation of normal and abnormal responses.

A method is described to obtain suitable parameter values for an adaptation model that can be used to simulate velocity step (VS) responses. The input parameters are the dominant time constant fitted to the first part of the VS response and the time of reversal in nystagmus direction. This method allows a particular solution for the model previously defined by others with a vestibulo-ocular reflex (VOR) time constant, a time constant of adaptation, and a fixed (unitary) gain of the adaptation element. However, because it might be arbitrary to assume a unitary gain, we also studied a more general model with a variable gain element. It appeared that patients showing short responses had a short VOR time constant and less adaptation than normal. Patients exhibiting prolonged responses appeared to have an excessively long VOR time constant and more adaptation than normal, presumably to compensate for the long time constant.