Saying nothing as is head of psychology, for example (6)
I believe the answer is:
silent
I believe this clue is a double definition.
'saying nothing' is the first definition.
(saying nothing is being silent)
'as is head of psychology for example' is the second definition.
(the first letter of 'psychology' is silent)
(Other definitions for silent that I've seen before include "as lead character in Psycho?" , "A continent" , "Unspeaking" , "Listen (anag.)" , "Mute" .)