apperception vs mental grasp

apperception

noun
  • The mind's perception of itself as the subject or actor in its own states, unifying past and present experiences; self-consciousness, perception that reflects upon itself. 

  • Psychological or mental perception; recognition. 

  • The general process or a particular act of mental assimilation of new experience into the totality of one's past experience. 

mental grasp

How often have the words apperception and mental grasp occurred in a corpus of books? (source: Google Ngram Viewer )