Each group watched variations of a slide show story that involved a young boy being hit by a car. Before and throughout the slide show, researchers collected saliva samples to measure alpha-amylase - a chemical that signifies a drop or rise in the fight-or-flight hormone norepinephrine, which increases a person's heart rate during emergencies or stressful situations.
Essentially, they wanted to see whether women responded differently to the slide shows and how they recalled them one week later.
Seven days after, scientists found the birth control group could recall the gist of the story, but not as many details as the non-birth control group. Women not on the pill seemed to remember more details to the story, including the presence of objects such as a fire hydrant near the scene of the accident in the slide show.
This difference may result from estrogen and progesterone interrupting how stress hormones are perceived by the brain.
Though birth control appears to affect what some women remember, it's important to note this type of contraception doesn't damage memory, as mentioned by one of the study's authors in a press release. Instead, the difference stems from which points are remembered most vividly, not from a deficit of what's remembered.