 The Molyneux problem has also been tackled by methods more amenable to experimental control than is possible in clinical studies, namely by rearing animals in darkness. Visual deprivation experiments have shown that during the development of the visual system there is a certain critical period in connection with the presentation of light patterns. During this period, changes brought about by deprivation can be reversed. If exposure to light is postponed for too long, however, the development of normal visual mechanisms will be extremely difficult, if not impossible. Although the results of deprivation experiments are not relevant to the solution of Molyneux’s problem—Molyneux supposed that his blind man had a good visual system, whereas that of deprived animals is abnormal—they have been used as evidence for Locke’s position.