I've long known a girl named Lily. I first met her in sixth grade, when she stopped homeschooling and came to my small, private school. She has never been diagnosed with an autistic spectrum disorder, and probably does not have one. But she is definitely closer to that side of the continuum than the neurotypical end.
Lily had spent her childhood either interacting with adults or playing with other children one-on-one. She preferred reading books to watching TV. As a result, although friendly and outgoing, she had no idea how to interact with others within the classroom environment. When she sat with other children at lunch, she would break the flow of conversation to make puns that they didn't get and not understand why everyone was staring at her. It didn't help that she talked like she had swallowed a dictionary and that--because she didn't watch TV--she knew almost nothing about popular culture (and often seemed bored by it). She was shunned by the girls she wanted to befriend and forced to sit with the geeky boys.
Lily quickly realized that she wasn't making any friends and that there were social norms she wasn't getting. I later found out that she consciously decided to learn what everyone else was doing and do it, too. Often a keen observer, she tuned in and quickly discovered a set of rules. Don't make jokes that other people don't understand. Use smaller words and put more breaks in your speech--don't talk formally or fluently. Compliment people on what they're wearing. Ask them more questions. Figure out what the conversation is about before you try to join in. Don't talk too loud or laugh too loud. And, later--avoid "geeky" topics like academic interests, your ideas about the meaning of life, fanfiction, anime, or video games, unless you know it's safe. Lily learned the rules both by closely observing people who had a lot of friends and by seeing why other people were shunned, often more cruelly than she was. She internalized these rules so deeply that by eighth grade, they felt like an "invisible current" dictating everything she did and "pushing" her to do things she didn't necessarily want to do, because she would feel everyone's disapproval if she did not obey them.
Lily never became friends with most of the people in her class, but she was accepted and treated with polite indifference by most. She became friends with a girl who helped her realize that the geeky boy's group to which they were both relegated were her real friends. They formed a close-knit group of misfits and weirdos of the sort you find in every junior high and high school.
In high school, Lily consistently found that her friends did socially unacceptable things far more than she did. Lily cared a lot about getting along with other people, and, knowing that most people did not understand and accept her for who she was, she responded by being quiet and saying only what she thought was safe. Her friends were a lot louder and, generally speaking, truer to themselves. Lily discovered she could tell immediately when her friends were committing a social faux pas. When her friend talked in a decibels-too-loud voice about Harry Potter fanfiction, drawing irritated looks from everyone in the hallway, it made her wince. When her bull-in-a-china-shop male friends left a mess all over her house and tried to edit the settings on her mother's computer (without a clue how rude their behavior was), she noticed and was embarrassed for them. A friend of hers walked funny, scuffing his feet strangely along the ground, and another bounced on the balls of his feet. A close friend of hers talked in an odd voice, with poor enunciation and odd breaks in the sentences, and while it did not bother her, it bothered her that she could see other people's reactions to it. Lily wondered if she was a disloyal friend.
But more than that, she noticed: she still had no idea how other people perceived her. The keener her perceptions of other people, the more she realized she had no idea what her body language, the tone of her voice, her dress or her choice of words said to people. She had consciously adapted the strategy of assuming the worst, which left her prone to depression, and she knew it wasn't the best solution, but she had no idea what else to do. Being polite, cheerful, and well-mannered, she rarely provoked cruelty from others, but she continued to have trouble making friends her own age, for reasons she did not understand.
Lily was a poor driver because she was slow to perceive large amounts of motion coming at her and determining a response. After a couple of close calls, she avoided driving as much as possible and went to college in a city where she could walk or take public transportation most places she needed to go. Lily was given poor reviews at a retail job she worked in high school. As a barista in a fast-paced store with lots of business, she could not seem to make the drinks quickly enough or move quickly between tasks such as cleaning the store and serving customers. When someone insulted Lily and she was forced to make a response, she froze up, trying to figure out the best response, and wouldn't think of an appropriate comeback until long after the fact. Lily was forever calling people back or sending up follow-up emails because of something she "didn't think of at the time" that turned out to be crucially important. She prefers email to phone conversations because it gives her more time to think about what she wants to say.
Lily is aware of her difficulties. She sees herself as the "eternal observer," in both the good senses (she likes noticing small details and talking and writing about them), and the bad senses (she feels she has trouble making decisions and acting on them).
People have suspected Lily has visual processing problems and that she tunes out her visual environment to focus on her thoughts. While this is true to some degree, she has a highly-developed aesthetic sense and is always pointing out features of the sky, trees, or buildings that those around her do not notice. Similarly, processing motion only seems to cause her problems when she has to navigate it, whether she's crossing the street or moving through a crowded mall. Visual processing problems per se are not the issue for her. Instead, she seems to have a problem with the link between perception and action.
I would argue that there are 3 levels of social ability that people with nonverbal learning disabilities can lack. The most basic is contemplating social behavior and other people's response to you, not in real time. This can occur when reading about characters, or when thinking about real acquaintances not currently present. Adam, for instance, is quite good at this, which is why he can talk intelligently about the psychology of characters in Pride and Prejudice. The midpoint is the ability to understand social behavior and other people's response to you in real time, but not feel personally involved and not have to act on it. Lily demonstrated this ability when she was embarrassed by her friends' social faux pas. Adam has some trouble with this. The 3rd, most difficult skill is being able to understand social behavior and other people's response to you in real time, when you are intimately involved and forced to act on it. This is where Lily falls apart. She can't represent herself in her physical and social situation in real time and act accordingly. The processing involved seems to overwhelm her, and she shuts down.
This 3 point continuum can explain the deficits of a lot of high-functioning ASD or ASD-like people like Adam or Lily. One of the influential theories of ASD is that people with it have a poor theory of mind. I'd argue that for people like Adam and Lily, who are empathetic and often think about other people's thoughts and motivations, theory of mind is intact-to-good. Anyone who can accomplish the most basic level probably has normal theory of mind. The problem is when they have to deal with 1) the pressure of processing in real-time (Adam), or 2) the pressure of being an actor in the scene (Adam and Lily).
The severity of a nonverbal learning disability might depend on where they fall on this continuum. Lily seems higher-functioning than Adam because she can process better in real-time. Neurotypical people outpace both of them because they can act in real time without difficulty.
I can't overemphasize the importance of acting. The difference between being an actor in a social situation and simply observing it is the difference between watching a movie and acting in the movie. The processing demands alone increase exponentially when you are forced to act. You have to view yourself from the outside (something someone like Lily has trouble doing), situate yourself in a 3-dimensional world, process your options for speaking and moving, consider other's possible responses, and then act--all in a matter of seconds. I think there may be more to Lily's difficulties than just processing demands, however. My guess would be that perceiving and acting (with all its self-representations) use many of the same brain areas, but are independent networks that can be separated by imaging the brain. My guess would be that Lily has an intact perceiving network, but her acting network is significantly impaired.
Perhaps ASD symptoms can stem from either a faulty perceiving network, a faulty acting network, or both.* The future of understanding and helping high-functioning people like Adam and Lily might come from researching these networks, more than from research on theory of mind.
*They may also have additional, more general sensory processing problems, which can interact and make things worse, but that's an extra complication.)