Psychological properties of ya
Psychological properties of yaBeyond Boredom:
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 that remained high through the rest of the trial. Also in agreement with the experimental data, the control subjects’ heart rate was not significantly affected by either of these actions. The results show that both yawning and two of its major physical components (opening the mouth and taking a deep breath) cause an increase in skin conductance, which indicates an increase in arousal.
The authors of this study did not provide a detailed analysis of the results or of the experiment’s possible flaws. They imply that the results agree with earlier research on the subject, such as the rat experiment previously mentioned. However, previous research suggested that yawning increased because of arousal; this study implies that arousal increases because of yawning. Furthermore, it is reasonable to question whether the testing methods of this experiment may have had an effect on the results. The study was conducted in a lab, and subjects were adorned with sensors and electrodes, creating an unnatural setting which may have made the subjects anxious (and consequently increased arousal levels).
Even though the study described above may have its imperfections, it is not completely useless in furthering our knowledge of why people yawn. It provides evidence from the physiological side of psychology to support a broad hypothesis that requires both biological and psychological evaluation. While the authors of the preceding study looked at the question of why organisms yawn strictly in physical terms, the authors of the second study examined the issue cognitively.
Based upon physical evidence from studies such as the one above, the authors of the second study (2) reasoned that yawning may be a mechanism to increase arousal when the environment does not provide adequate stimulation, but where arousal is desired or necessary. A self-report study was performed to show the correlation between stimulation in the environment and frequency of yawning. They predicted that the frequency of yawning would be high in situations where there is little stimulation and lower when more stimulation was present.
Daily journals of activities and yawns were kept by 28 college students (25 female and 3 male) for one week. Each time they yawned, the subjects recorded the time of day and the activity in which they were engaged. In addition, they kept track of what time they awoke and went to sleep. It should be noted that, while this self-reporting method may not seem reliable because of its subjective nature, previous studies have shown that such procedures are valid.
Three trends appeared in the data collected from the journals. First, there appeared to be no relationship between the number of yawns per day and the amount of sleep the subjects had the previous night. Second, the activities in which subjects were engaged when they had the highest yawning frequency tended to be more monotonous and less stimulating than those in which subjects yawned less. For instance, subjects yawned most when sitting in class (21% of all yawns), driving (16%), and watching TV (13%). Activities that produced a lower frequency of yawning, on the other hand, were cooking, cleaning, having a conversation, and thinking. The third observation from the data was that yawns were not evenly distributed during the subjects’ days—they were most frequent during the first hour after waking and the hour immediately before going to sleep.
Several conclusions can be drawn from these results that support and elaborate upon the authors’ hypothesis. As predicted, tasks that are “boring” and have little social interaction make subjects more prone to yawning. Contrary to their nature, though, these tasks often require one to pay close attention. As the authors suggested, yawning may be a mechanism to induce arousal when attentiveness is necessary and the environment lacks stimulation. The fact that yawning frequency is highest in the hour after awaking and the hour before going to bed provides further support for this theory. For example, since subjects are naturally becoming sleepy in the hour before retiring (thus causing the arousal level to drop), the yawn may be the body’s way of resisting fatigue by inducing arousal. Once the subjects went to bed no yawns were reported; they had, in effect, “given in” to being tired and no longer needed to induce arousal. Finally, since yawning frequency did not change with amount of sleep the previous night, the results of the study suggest that yawning is not related to sleep depravation.
This study provides valuable evidence to support the theory that yawning is a mediator of arousal. However, its results would have more credibility if the authors had used a larger and more diverse sample. The sample consisted overwhelmingly of females, and although no studies had yet shown that yawning patterns differ between the sexes in human beings, research has suggested that gender differences exist in the yawning patterns of rats and fish. Since the study that follows confirms the conclusions drawn above, these shortcomings can be overlooked.
The authors of the final study (3) tie together the two studies above and make new conclusions based upon the findings. By measuring both physical and psychological factors, the study sought to provide evidence for two theories: first, that yawning is associated with changes in activity levels, and second, that yawning is not affected by sleep depravation. One of the foundations for their assertion that yawning increases with frequent shifts in activity come from observations of different species of mammals. Sedentary animals, such as herbivores, rarely yawn; carnivores, on the other hand, constantly switch between periods of activity and inactivity and were found to yawn much more. The authors performed a two-part correlational study to determine the specific link between activity levels and yawning in humans. Like the authors of the previous study, they predicted that yawning would increase during low activity levels and decrease when subjects were more active. They also predicted that amount of sleep would not affect how much subjects yawned.
The first experiment of the study included six professional adults (three male and three female) aged 29 to 55. Subjects wore a device called a Monologger Actigraph, which consisted of a button that subjects pressed every time they yawned and a monitor that measured activity level as expressed by heart rate. The devices were worn 24 hours a day for two weeks. The second part of the study used a self-report method to determine if there is a connection between sleep depravity and yawning. 17 male and 28 female college students recorded the amount of hours slept each night and the number of times they yawned each day. (The time awake was calculated by subtracting the time slept at night from 24 hours; naps were not accounted for.)
The results of both experiments concur with the authors’ predictions. In the first part of the study, nearly all of the yawns examined were followed by an increase in activity within fifteen minutes of the onset of the yawn. Out of 704 yawns, only 43 did not precede such an increase. In agreement with previous experiments, the authors noted that the most frequent periods of yawning were in the hour after waking up and the hour before going to bed. The second part of the study, also concurring with previous research, showed that there is no correlation between amount of sleep and frequency of yawning. The subjects’ frequency of yawning was nearly the same on weekdays and weekends, even though they slept significantly more on the weekends.
This data shows a simple relationship between yawning and activity level, and it can be concluded that yawning is a reliable predictor of an upcoming increase in activity level. Therefore, the authors suggest that yawns serve as a marker of a change in activity level, as well as being regulators of arousal. The study also disproves the common notion that sleep deprivation is a cause of yawning. The results clearly indicate that yawning frequency does not change when the amount of sleep changes.
As was the case with the previous study, the results of this experiment would be more accurate with the use of a larger and more diverse sample, particularly in the first experiment. Although the gender ratio was equal this time, all subjects were “professionals” who led very similar lifestyles. To get an accurate representation of the human population, people of different lifestyles and professions should be included in the sample.
The studies described above provide conclusive evidence that yawning is closely related to increases in activity and arousal levels. For the most part all results are an agreement, but one minor discrepancy should be clarified. In the first study it was shown that yawning had no affect on heart rate, yet in the third study heart rate was used to show an increase in activity level. These results do not contradict each other because the first study was aimed at finding whether yawning itself had a direct affect on heart rate, while the third study used heart rate as an indicator of increase of activity from external sources. Yawning itself apparently does not cause in increase in heart rate. It does, however, indicate an increase in general arousal—often the result of an increase in activity—which causes the heart rate to go up.
Psychologists and physiologists have taken the findings from these studies and built upon them to from more definitive hypotheses about yawning and its origins and functions. It has been more recently suggested that yawning is related to cortical arousal—that is, the flow of blood to the cerebral region of the brain. If this is true, than the function of yawning serves the extremely important purpose of helping the most sensitive region of the body maintain proper blood pressure. In addition, evolutionary biologists have proposed that yawning has become such a frequent and important part of animal physiology because it serves a protective purpose. In some situations that lack the necessary external stimulation, low arousal could threaten an animal’s life. According to this theory, yawning has evolved as a guard against inattentiveness by inducing arousal in certain situations. A modern example of this is driving; stimulation is low, yet failure to pay attention is extremely dangerous.
Based on the evidence presented by the three studies evaluated, some general conclusions about the nature of yawning can be drawn. Apparently yawning serves as both a mechanism to induce arousal and an indicator of an increase in activity levels. In addition, the common notion that yawning is associated with sleep depravation has been debunked. However, the study of yawns is a relatively new field of research for the psychological and scientific community, and more research is necessary to determine the exact purpose of its existence.