Studies on the physical and psychological properties of yawning
The act of yawning has been observed in all vertebrates, and occurs in humans as early as minutes after birth, so it must have some definitive physiological purpose. Until recently, most scientists believed yawning was a respiratory function, triggered by a surplus of carbon dioxide in the bloodstream. In the past decade, however, studies have suggested that yawning acts as a mediator of activity and arousal levels. The evaluation that follows will examine three such studies and the evidence they contribute to this hypothesis.
The first study (1) examined the connection between yawning and activity on a physical level. Previous research had drawn loose ties between arousal and yawning; for example, one study showed that yawning in rats increased with the presence of a penile erection. To show that arousal increases with the onset of a yawn, the authors of this study designed a correlational experiment to measure changes in physical indicators of arousal before, during, and after yawning. They predicted that signs of arousal would increase when the yawn started.
A mixed-gender group of 30 college students participated in three 15-minute laboratory trials which measured skin conductance and heart rate, two physical correlates of arousal. In each trial, subjects pressed a button when they felt a yawn coming on, and equipment in a nearby room took readings from sensors attached to their fingertips. The first trial measured skin conductance, the second trial measured heart rate, and the third trial used an electromyogram with electrodes attached to the subjects’ masseter muscles to verify that they were yawning when they said they were. Each subject was alone in a room for the course of all three trials. In addition, a control group of 20 students were tested for skin conductance and heart rate while intentionally performing different physical aspects of yawning, such as opening the mouth wide and taking deep breaths. All results were analyzed using a Friedman ANOVA test.
The results of the experiment partailly concur with the authors’ prediction. In the experimental group, it was found that skin conductance values during and after the first yawn were significantly higher than before the yawn. For each subsequent yawn, the difference between pre-yawn and post-yawn values decreased. In other words, once the skin conductance values rose with the initial yawn, they remained consistently high through the rest of the trial. However, no significant change in heart rate was measured during the subjects’ initial yawns, and no effects became apparent with successive yawns. Interestingly enough, the control group provided very similar data. The results showed that during both the opening-mouth and deep breathing trials, control subjects experienced an initial increase in skin conductance with the first yawnlike action...