perceptual set

A perceptual set is a tendency to perceive or notice some aspects of the available sensory data and ignore others. It is heavily influenced by expectations, past experience, and context. If an object is completely outside a person's prior experience (their “set”), they may not select it for conscious attention — effectively rendering it “invisible” to the mind's eye, even if the retinas physically register it.

This principle gives the archive its name. In an often-told story — variously attributed to the arrival of Magellan's ships off Tierra del Fuego and to Captain Cook's Endeavour off the Australian coast — the people onshore are said to have been unable to see the European vessels at first, because nothing in their prior experience had prepared them to perceive such a thing, until someone learned to recognize the strange disturbance on the water and taught others where to look. The anecdote is almost certainly apocryphal, but the principle it dramatizes is real and measurable.