Hardening one's Heart

I'm up to Exodus 9 so far, and I'm interested in the various words used to harden Pharaoh's heart.  Now the heart was the centre of will and decision-making for the ancient Hebrews, so the hardening of the heart is making the brain hard -- block-headed (thank you Ehud for this image!), stubborn.  Not evil -- but stubborn, obstinate, pig-headed.

Sometimes Pharaoh's heart is or remains hard.  Sometimes God hardens it for him.  Sometimes Pharaoh hardens it himself.  I searched "harden* + heart" in Accordance (my Bible software) and came up with 19 hits in the book of Exodus (from 4:21 to 14:17).

The most common verb used is חזק hh-z-q, which has "be strong" as its basic meaning.  To be strong, grow strong, or harden. (12 times)

The next word (which appears both in verb and adjective form) is כבד kh-v-d, which means to be honoured.  It usually has a very positive meaning.  But it also means to be heavy or... to be dull! Pharaoh dulls his heart. (6 times)

The final word is קשׁה q-sh-h which is the most straightforward, and just means to be heavy or hard.  It only appears once.

It's a shame that English translations don't make any distinction here.