Sentence:  Hereby , the external object viewed by the eyes remains the thing that is seen , not the retinal image , the purpose of which would be to achieve perceptive cooperation by stirring sympathetic impulses in the other sensory centers , motor tensions , associated word <WSD>symbols</WSD> , and consciousness . 
Meaning of the word marked with <WSD> tags:  an arbitrary sign (written or printed) that has acquired a conventional significance