We pointed out that language acquisition is central to the demonstration of the biological nature of language.The child, exposed to language through the environment, processes the input using biologically endowed systems for language acquisition (Universal Grammar and acquisition strategies), and the eventual outcome is a grammar and a lexicon.Although there are differences of views among psychologists, they agree that language is acquired under the guidance of global grammar rules: innate knowledge of language, and child acquisition strategies imposing an input structure.During an infant's first month of life, visual input triggers important changes in how the brain organizes stimuli that enter from the left versus the right eye, and eventually the baby is able to perceive perspective, distances, and depth.For example, the biologi- cally based system for human vision is already well developed at birth, but newborns cannot differentiate the input they receive from their left versus their right eye, so they have no depth perception.