Calvillo et al. designed a study to compare vulnerability to the misinformation effect in those who have slept and those who have not. They studied four different groups with a varying retention interval for a series of images. Some intervals were overnight, which created a "sleep" condition. Participants responded to true/false questions about the event based on their memory of the images. Some of the statements coincided with the images, some were inconsistent, and others were foils.