The Critical Period hypothesis suggests that language, spoken or signed, is more easily acquired as a child at a young age versus an adult because of the plasticity of the child's brain. In a study done at the University of McGill, they found that American Sign Language users who acquired the language natively (from birth) performed better when asked to copy videos of ASL sentences than ASL users who acquired the language later in life. They also found that there are differences in the grammatical morphology of ASL sentences between the two groups, all suggesting that there is a very important critical period in learning signed languages.