Volunteers taking part in the Deept Time experiment in the Lombrives cave in south-west France

15 people from different backgrounds recently left a cave in southwest France after 40 days underground.

The experiment should show how the lack of clocks, daylight and external communication affects the participants’ sense of time.

Project leaders Christian Clot and Marina Lançon, one of the volunteers in the study, shared their experiences with BBC World News.