Sentence:  Psychical blindness is a condition in which there is a total absence of visual memory-images , a condition in which , for example , one <WSD>is</WSD> unable to remember something just seen or to conjure up a memory-picture of the visible appearance of a well-known friend in his absence . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)