Sentence:  The authors set about answering this fundamental question through a detailed investigation of the patient 's ability , tactually , ( 1 ) to perceive figure and ( 2 ) to locate <WSD>objects</WSD> in space , with his eyes closed ( or turned away from the object concerned ) . 
Meaning of the word marked with <WSD> tags:  a tangible and visible entity; an entity that can cast a shadow