When people are asked to report on their mental processes, they cannot access this unconscious activity.
The large proportion of subjects who were taken in by the deception contrasts with the 84% who, in post-test interviews, said that hypothetically they would have detected a switch if it had been made in front of them.
They were given a closer look at their "chosen" photograph and asked to verbally explain their choice.
However, in some trials, the experimenter had slipped them the other photograph rather than the one they had chosen, using sleight of hand.
Although some other experimental work followed from the Nisbett and Wilson paper, difficulties with testing the hypothesis of introspective access meant that research on the topic generally stagnated.
He instead relied on the theory that the adaptive unconscious does much of the moment-to-moment work of perception and behavior.