How are drawings interpreted through psychology?

actually, i dont really know how, but as far as i am concern on this topic standing as a charcoal painter... i am also curious. though there are things that my friend had told me. first by the tension that the drawer had used if he used to draw with a tight hold on the pencil... the brightness of the color may varied... then the drawing itself which every objects means a lot... the position of the objects and its size... i hope its a starting idea. enjoy mylot!