When I was younger I had a great deal of trouble recognizing facial expressions. For example, it was hard for me to tell whether someone was smiling or barely managing to hold back tears. I could usually figure out which was which from context, at least when the emotions involved were so different. With nuances like the difference between a smirk and a grin, I was completely unable to tell the difference. Ditto for picking up emotional content from intonation and vocal tone.

As a teenager I trained myself to recognize specific small details that reliably distinguish between otherwise similar-looking expressions; tightened muscles, gaze direction, shoulder height and angle, things like that.

I've been diagnosed with Asperger's, ADHD, and delayed sleep phase disorder.