 Strictly speaking, the experimentally verified critical period relates to a time span during which "damage" to the development of the visual system can occur, for example if animals are deprived of the necessary binocular input for developing stereopsis.It has however been considered "likely", and has in many cases been flatly presented as fact, that experimental evidence would point to a comparable critical period also for "recovery" of such development and "treatment"; however this is a hypothesis.Recently, doubts have arisen concerning the validity of this critical period hypothesis with regard to visual development, in particular since the time it became known that neuroscientist Susan R. Barry and others have achieved stereopsis as adults, long after the supposed critical period for acquiring this skill.