On the ancient history of the direction of the motion aftereffect.

Scientists agree that Aristotle in his Parva Naturalia was the first to report a visual illusion known as the motion aftereffect (MAE). But there is less consensus as to who was the first to report the direction of the MAE. According to some, Aristotle only described the phenomenon without saying anything about its direction. Others have defended the position that Aristotle did report a direction, but the wrong one. Therefore, it has been suggested that Lucretius in his poem De Rerum Natura was the first to report the correct direction of the MAE. In this paper it is shown why and how it can be inferred that Aristotle did not write about the direction of the MAE, only about its occurrence. It is also argued that it is indeed likely that Lucretius was the first person to report the direction of the MAE. However, this is not as obvious as it might appear at first sight.