Note 17 — Chapter IV
Reading edition
Die Schein-Bewegungen, von Professor Dr. J.I. Hoppe (1879); cf. an ingenious article on "Optical Illusions of Motion," by Professor Silvanus P. Thompson, in Brain, October, 1880. These illusions frequently involve the co-operation of some preconception or expectation. For example, the apparent movement of a train when we are watching it and expecting it to move, involves both an element of sense-impression and of imagination. It is possible that the illusion of table-turning rests on the same basis, the table-turner being unaware of the fact of exerting a certain amount of muscular force, and vividly expecting a movement of the object.