Visual identification rate in search of a missing stimulus

Subjects searched for a digit which was not presented in an array of nine different digits. The identification rate was estimated from the percent correct. Well-trained subjects identified 6.5 digits with a 50-msec. exposure. This fast identification rate was expected from our procedure using a single answer, an inconsistent target, and equal probability that every digit would be a target. Naive subjects markedly improved their performance in the first two weeks of the trials which were given for a total of 24 days.