The most difficult aspect of learning American Sign Language is adjusting to using hands and facial expressions as the main mode of communication. Instead of listening, we have to learn to recognize and read the visual signs.
The professor will occasionally go around the room to ask quick questions using the vocabulary we have just learned, such as “What is your favorite color?” or “How are you feeling”. I find that even I’ve prepared an answer in my head, it is sometimes difficult to produce my answer through sign language in a smooth and natural way. Often, I will feel paralyzed when put on the spot, trying to think as quickly as possible as to how I’m supposed to move my hands to communicate. Also, as a beginner, I tend to concentrate on the hand movements and forget that facial expressions are just as important in signing.
One of the difficulties that may be related to crosslinguistic differences is getting used to the grammatical structure of ASL. For example, while in English one would ask “What is your name?”, in ASL one would sign “Your name what?” Such differences in syntax and grammar apply in many different situations and though the ASL grammatical form seems logical, sometimes thinking in English while signing causes me to sign incorrectly. Some more examples of grammatical differences can be seen in “You tired?” (ASL) rather than “Are you tired?” (English), and “How you?” (ASL) rather than “How are you?” (English).
Overall, I think crosslinguistic differences in having English as the L1 has a relatively minor impact on learning ASL (positive or negative). Because the form of communication is so different, it seems like there is little overlap that can be confused between the two languages.