Sentence:  The mediums with whom the Parapsychology Foundation is <WSD>working</WSD> in this experiment are in a waking or only slightly dissociated state , so that the sitter can make comments , ask and answer questions , instead of talking with a `` control '' who speaks through an entranced sensitive . 
Meaning of the word marked with <WSD> tags:  exert oneself by doing mental or physical work for a purpose or out of necessity