Fixation vs Special Interest

The terms fixation and special interest tend to be interchanged, especially among neurotypicals talking about autism. They are similar, but have fundamental differences. 

A synonym for a fixation is to hyper-focus on something. I think that phrase is more self explanatory and easy to understand. To fixate on something is a relatively short term experience of intense focus on a specific task or item. This is usually marked by an extreme lack of awareness of the surrounding environment and extreme annoyance at any interruptions. 

A special interest is similar to a fixation in the sense that it involves an intense focus, but it is more long term and has other specific characteristics. A special interest is something that the person will enjoy for a long period of time, often ignoring other interests. They may “info-dump” about this interest, which is when the individual talks very fast and excitedly about a topic and the listener struggles to “get a word in”. 

I think the easiest way to understand these differences is through an example. A fixation on a movie series could look like someone watching the entire franchise in one sitting, ignoring their family and their environment and not taking any breaks. A special interest in that same movie could look like the person only ever talking about the movie and watching it every single night for months. As you can see, these experiences are related to each other, but are fundamentally different. A person can have one but not the other.