Inattentional blindness, or perceptual blindness, is when a person does not see something in plain sight. The term is only used for a lack of attention, not for any physical defect of vision. The term was used as a book title.^[1]

It is a basic fact of psychology that the "world provides an infinite array of things that might capture attention. Attention is, however, an inherently limited capacity".^[2] The mechanism as to what to notice is partly or largely inherited. The usefulness of a particular behaviour is in an “ecology of evolutionary adaptiveness” for ancestral hunter-gatherers.^[3] Old world monkeys, who show fear of snakes and have an advanced visual system, evolved in Africa under continual pressure from snakes. Some mammals evolved physiological resistance to snake venoms, but African apes improved their ability to see snakes visually before the snakes could strike.^[4]