Sentence:  When words can be used in a more fresh and primitive way so that they strike with the force of sights and sounds , when tones of sound and colors of paint and the carven shape all strike the sensibilities with an undeniable force of data in and of themselves , compelling the <WSD>observer</WSD> into an attitude of attention , all this imitates the way experience itself in its deepest character strikes upon the door of consciousness and clamors for entrance . 
Meaning of the word marked with <WSD> tags:  a person who becomes aware (of things or events) through the senses