ASL is a visual, spatial language, unlike languages likes French or Spanish, which are both written, oral languages. Therefore although both language modes require cognitive ability, ASL requires that the student puts the entire body to work including all features of the face such as the mouth, eyes and eyebrows to recreate the language accurately. Also how to use the space in front of the interpreter is required when learning a feature of the language called Constructed Action/Dialogue (implemented during storytelling). The cultural aspects of a disenfranchised community are learned as well. This is necessary for the student because it impacts how the student should interact with the native user of ASL.
Learning to interpret ASL into English or visa versa, has completely different challenges because the brain of the interpreter has to function in two capacities at the same time - retaining the language being seen while translating it into one that can be heard or visa versa. The translation of oral languages usually takes place consecutively whereas the translation of ASL is simultaneous. This requires separate skills and training such as short term memory being developed to complete this task effectively.
