Yawning is a reflexive action that is often associated with sleepiness. when a person yawns, the mouth opens, and a longer than normal breath of air is inhaled, followed by a longer than normal exhalation. hypothesizing that yawning has a regulatory mechanism similar to breathing, scientists conducted an experiment on college students to test the effect of ambient carbon dioxide levels on yawning. the scientists investigated carbon dioxide levels in their experiment because high carbon dioxide levels in the signal control centers in the brain to increase rate and depth of inhalations and exhalations.