Failure to register consciously a visual stimulus when attention is focused elsewhere. The term was coined in the title of the book Inattentional Blindness (1998) by the US psychologists Arien Mack (born 1931) and (posthumously) Irvin Rock (1922–95). In Mack and Rock's standard experimental procedure, a small cross was presented briefly on a computer screen, and participants were asked to judge which of its component lines was longer. After several similar trials, an unexpected image, such as a brightly coloured rectangle or an inverted face, appeared on the screen along with the cross. The participants, who were concentrating on the cross, often failed to notice the unexpected image, even when it appeared in the centre of the visual field, although a personally meaningful image, such as the participant's own name or a non-inverted happy face, was usually noticed. This phenomenon may help to explain why motorists and train drivers sometimes go through red traffic signals and why certain other accidents occur. See also visual search. Compare change blindness, motion-induced blindness.