Sentence:  Therefore , if the sense of touch is functioning normally and there is a complete absence of spatial awareness in a psychically blind person when the eyes are closed and an object is handled , the conclusion seems unavoidable that touch by itself cannot focus and take possession of the third-dimensionality of things and that actual sight or visual representations are <WSD>necessary</WSD> . 
Meaning of the word marked with <WSD> tags:  absolutely essential