visual field: all of the points of the physical environment that can be perceived by a stable eye at a given moment
visual percept: a percept that arises from the eyes; an image in the visual system
julian calendar: the solar calendar introduced in Rome in 46 b.c. by Julius Caesar and slightly modified by Augustus, establishing the 12-month year of 365 days with each 4th year having 366 days and the months having 31 or 30 days except for February