“He was very helpful to me because he could talk about it, talk about what he was observing, in a way that made me understand how I was being observed by the outside world,” Mr. Picker said.

“I had a very difficult childhood, and it stayed with me, well, it will stay with me forever,” he added. “But knowing Oliver, being able to, to spend time with Oliver, and to be, just to be in the presence of his greatness, made me feel better about myself.”

Dr. Greene, the physicist, said that he was “awe-struck” when he met Dr. Sacks, who he said had “a ferocious talent and a rare gift” for finding beauty and humanity in the stories of people given diagnoses of illnesses like autism, Tourette’s or encephalitis lethargica — the disease that afflicted the patients in his book “Awakenings.”

The two men chatted over cocktails, Dr. Greene recalled, and Dr. Sacks mentioned that he had finished Dr. Greene’s book “The Elegant Universe” just that day. He had liked it, Dr. Sacks said, but he added that the book was “slippery.”