Sentence:  First I make preliminary watercolor sketches in quarter scale ( approximately * * f inches ) in which I pay particular <WSD>attention</WSD> to the design principles of three simple values - the lightest light , the middle tone , and the darkest dark - by reducing the forms of my subject to these large patterns . 
Meaning of the word marked with <WSD> tags:  the process whereby a person concentrates on some features of the environment to the (relative) exclusion of others