Unscientific guess from a person with a balanced, healthy life, but some internal challenges still present after years of serious, focused healing work from childhood trauma: So, why do people with BPD (and/or PTSD) feel uncomfortable or misread ambivalent facial expressions? Traumatized, hypervigilent people use the clear emotions of others to assess safety and know how to quickly respond based on a scale of threat vs comfort. As strange as it may sound to the non-traumatized person; a degree of anger can feel safer than the unknown of an ambivalent face, "I know what that (anger) is and what particular coping skills keep me safe around this person." But ambivalent faces can seem to communicate hiding, or trickery. Those faces leave me feeling unsure and anxious for a face change that tells me what I am dealing with and how to respond. Can I hug them or should I be careful around them and avoid eye contact? Not knowing can feel uneasy or even scary.

I have noticed, over the years, that I tend to take more negativity from blank faces than other seem to. Not diagnosed with BPD or any other personality disorder. Suffered a great deal over the years, though, with internal things. Now over 50 much less intense.

Emotional recognition is consistent across expression and tone (e.i. talking on the phone)

Have you looked into vitamin deficiancies ? My daughter started taking vitamin B12 and her entire mood changed, she is social now and not depressed or moody anymore. She is also a straight A student on the honor roll.