Shermer and Alderson-Day discuss the psychologist's journey to understand the phenomenon of sensed-presence: the disturbing feeling that someone or something is there when we are alone. Using contemporary psychology, psychiatry, neuroscience, and philosophy, Alderson-Day attempts to understand how this experience is possible. Is it a hallucination, a change in the brain, or something else? The journey to understand takes us to meet explorers, mediums, and robots, and step through real, imagined, and virtual worlds.

Ben Alderson-Day is an Associate Professor in Psychology and a Fellow of the Wolfson Research Institute for Health and Wellbeing at Durham University. A specialist in atypical cognition and mental health, his work spans cognitive neuroscience, psychiatry, philosophy, and child development. His new book is Presence: The Strange Science and True Stories of the Unseen Other.