Impaired vision and blindness are common. About 3.4 million people in the US are blind or visually impaired. Vision is usually measured by visual acuity charts, and normal vision is expressed as 20/20 ...

Humans and many other animals possess an innate ability to rapidly perceive numerosity: the number of objects in a visual scene. Numerosity perception is influenced by adaptation, whereby previously ...

The adverse impact of adjacent contours on letter visual acuity is known as crowding but there is conflicting evidence that foveal crowding may be reduced or disappears under low contrast conditions.