medieval philosophy, perception, attention, Albertus Magnus, Roger Bacon, Peter Olivi, visual field, medieval optics, extramission

Is vision merely a state of the beholder’s sensory organ which can be explained as an immediate effect caused by external sensible objects? Or is it rather a successive process in which the observer actively scanning the surrounding en-vironment plays a major part? These two general attitudes towards visual perception were both developed already by ancient thinkers. The former is embraced by natural philosophers (e.g., atomists and Aristotelians) and is often labelled “intromissionist,” based on their assumption that vision is an outcome of the causal influence exerted by an external object upon a sensory organ receiving an entity from the object. The latter attitude to vision as a suc-cessive process is rather linked to the “extramissionist” theories of the proponents of geometrical optics (such as Euclid or Ptolemy) who suggest that an entity – a visual ray – is sent forth from the eyes to the object. The present paper focuses on the contributions to this ancient controversy proposed by some 13th century Latin thinkers.