page_title: Perceived visual angle
section_title: Perceived measures
hierarchical_section_title: Perceived visual angle / Perceived measures
context_page_description: In human visual perception, the visual angle, denoted θ, subtended by a viewed object sometimes looks larger or smaller than its actual value. One approach to this phenomenon posits a subjective correlate to the visual angle: the perceived visual angle or perceived angular size. An optical illusion where the physical and subjective angles differ is then called a visual angle illusion or angular size illusion.
  Angular size illusions are most obvious as relative angular size illusions, in which two objects that subtend the same visual angle appear to have different angular sizes; it is as if their equal-sized images on the retina were of different sizes. Angular size illusions are contrasted with linear size illusions, in which two objects that are the same physical size do not appear so. An angular size illusion may be accompanied by a linear size illusion at the same time.
  The perceived visual angle paradigm begins with a rejection of the classical size–distance invariance hypothesis, which states that the ratio of perceived linear size to perceived distance is a simple function of the visual angle.
context_section_description: Figure 2 diagrams the perceived (subjective) values for a viewed object.
  Point O′ represents the place from which the observer feels that he or she is viewing the world. For present purposes, O′ can represent the cyclopean eye (Ono, 1970, Ono, Mapp & Howard, 2002).
caption: Figure 2: Subjective values