The writer's getting on, showing representational technique (7)
I believe the answer is:
imaging
'representational technique' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'the writer's getting on' is the wordplay.
'the writer's' becomes 'im' (both could mean 'the crossword setter is').
'getting on' becomes 'aging' (I've seen this before).
'im'+'aging'='IMAGING'
'showing' acts as a link.
Can you help me to learn more?
(Other definitions for imaging that I've seen before include "Taking a picture of" , "Making pictures" , "Creating a picture" , "Forming a picture of (something)" , "Forming a mental likeness of (something)" .)