Parametric adjustments in the oculomotor system.

Publisher Summary Appropriate optical techniques are now available with which to challenge many of the major parameters governing oculomotor function. In many, but not all, instances it is known that the nervous system is able to respond positively to this challenge through adaptive processes that operate directly on the gain of the parameter in question. Such adaptive gain control has been demonstrated in a rich variety of species, including fish, birds and mammals. Carefully selected visual challenges generally elicit equally selective adaptation, but not always. Much of the initial interest in adaptive phenomena was motivated by concern with so-called plastic mechanisms underlying long-term learning, but it is clear that not all of the responses are necessarily of this type. Long-term plastic adjustments occur over hours or days, and show good retention of the altered state when the subject remains in darkness or is otherwise deprived of visual feedback. Presumably, slow changes of this kind are solely concerned with the maintenance of long-term stability. Furthermore, saccades are not necessary: the post-saccadic enhancement effect could be evoked by merely shifting the visual scene in a saccade-like way. Such observations suggest the need for extraordinary attention to detail when examining oculomotor responses.