poker face vs unemotional

poker face

noun
  • Any similar expression used to prevent giving away one's motives, feelings, or situation. 

  • An impassive facial expression cultivated to prevent other players from determining whether one's actions in the game are the result of a quality hand, or of bluffing. 

unemotional

adj
  • Showing little or no feeling. 

  • Reasoned and objective, involving reason or intellect rather than feelings. 

How often have the words poker face and unemotional occurred in a corpus of books? (source: Google Ngram Viewer )