Some Antecedents and Consequences of Yawning

Attempts were made in three experiments to induce human subjects to yawn reliably in the laboratory. In subjects who believed they were not observed, reading about yawning did increase their frequency of yawning, compared to reading about scratching or day dreaming. In the second experiment, performing a spontaneous yawn decreased skin conductance, but "faked" yawns did not have this effect. In subjects under observation during the third experiment neither boredom, vigilance, nor reading about yawning induced the act. Article It is commonly believed that yawning is caused by boredom, lack of oxygen, and seeing other persons yawn. Such an oddly disparate set of antecedent stimuli might seem to, make yawning a focus of interest for those who study biosocial aspects of behavior. But this has not been the case, and relatively few psychologists have studied yawning. As a result we are still uncertain about the precise circumstances under which these common beliefs about yawning are true (or not true). Provine, Tate, and Geldmacher (1987) found that changes in oxygen and carbon dioxide levels did not affect yawning frequency, whereas Provine and Hamernik (1986) found that concentration on boring stimuli, such as TV test patterns, did increase yawning frequency. A comparably diverse set of neuroendocrine pathways has been found to regulate yawning. Neurotransmitters such as dopamine (Yamada, Nagashima, Kimura, Matsumoto, & Furukawa, 1990), acetylcholine (Cowan, 1978; Urba-Holmgren, Gonzalez, & Holmgren, 1977), and serotonin (Urba-Holmgren, Holmgren, & Gonzalez, 1979) have been implicated, as well as steroid hormones such as estrogen and testosterone (Phoenix & Chambers, 1982), oxytocin (Argiolas, Melis, Stancamp, & Gessa, 1990), and ACTH or adrenocorticotrophic hormone (Argiolas, Melis, & Gessa, 1988). Yawning has been found in all the major vertebrate classes, including several mammalian orders (e.g., primates, carnivores, and rodents), fish (Baenninger, 1987), birds (Dumpert, 1921), reptiles (Barthalmus & Zielinski, 1988), and amphibians (Cramer, 1924). Thus, the evolution and physiological correlates of yawning both present intriguing questions. In itself, the fact that so many apparent mechanisms are associated with yawning, in so many different species, suggests that the act is of some general importance. In primates yawning may have evolved as a form of nonverbal communication. Deputte (cited by Redican, 1982) found that yawning was contagious among individual nonhuman primates of similar age and social status. He interpreted this contagion as an adaptive means for synchronizing activities (especially the sleep/waking cycles) of the individuals in a mobile troop of primates. One implication of this view is that troop leaders would likely initiate more yawning than subordinates, and Hadidian (1980) found that this was the case. Males also yawn more than females among nonhuman primates, although not in humans (Schino & Aureli, 1989). Dominant males may simply be making more threat displays that involve mouth opening, although Phoenix and Chambers (1982) found that testosterone injections increased yawning frequency by both male and female rhesus macaques. Sauer and Sauer (1967) proposed that yawning induces relaxation of social tension in groups. This would account for yawning contagion, but does not explain why nonsocial animals would yawn, or why social animals, such as humans, yawn when they are alone. In humans yawning also has a social contagion aspect. Moore (1942) reported that people in college libraries and church services yawned in response to seeing a trained actor yawn. But Moore's observations were rather poorly controlled and have proved difficult to replicate within the confines of the laboratory. In our laboratory we have consistently failed to find contagion of yawning when human subjects are being openly observed; in one study an actor yawned during a reading delivered in person or via TV and there were virtually no yawns in response by 40 laboratory subjects (Baenninger, 1987). In the studies reported here we have attempted to increase the frequency of solitary human yawning as a way of gaining stimulus control over the act; the relatively low baseline frequency of yawning is, of course, a stumbling block for research. In these studies we have also begun to examine some physiological correlates of yawning as a way of trying to understand what bodily functions it may serve.