Another word describing an expressionless person?

Question

Is there a more scientific adjective or noun to describe a person whose emotion cannot be seen on their face? You know, the kind of person you can't tell whether they're angry or content because they involuntarily have the same expression on their face the whole time.

Any help would be appreciated!

Answer 1

numb

soul-less

vacant

wrinkle-free

still

Answer 2

stone-faced