ken vs visual field

ken

noun
  • Range of sight. 

  • Youth or children's group. 

  • A Japanese unit of length equal to six shakus 

  • Knowledge, perception, or sight. 

  • The tsurugi 

verb
  • To know, perceive or understand. 

visual field

noun
  • field of vision, field of view 

How often have the words ken and visual field occurred in a corpus of books? (source: Google Ngram Viewer )