Improvisation of claviers, instinctive (8)
I believe the answer is:
visceral
'instinctive' is the definition.
(I've seen this before)
'improvisation of claviers' is the wordplay.
'improvisation of' indicates anagramming the letters (I've seen this in other clues).
'claviers' is an anagram of 'VISCERAL'.
(Other definitions for visceral that I've seen before include "Relating to deep inner feelings" , "Relating to internal organs of the body" , "Of the internal organs (esp. guts)" , "Relating to the guts" , "Appertaining to the guts" .)