Sign. 1. A sudden, deep inhalation of air accompanied by an open mouth, tightened cheek muscles, eye closure, and tearing. 2. An involuntary deep breath due to sleepiness, fatigue, boredom, or emotional conflict. 3. A socially contagious gaping behavior, often difficult to suppress.
Usage: Usually a sign of drowsiness, yawning also occurs, e.g., in tense business meetings as a sign of mild anxiety, disagreement, or uncertainty. When alert listeners yawn in response to controversial suggestions or ideas, the yawn signals a probing point, i.e., an opportunity to explore unverbalized objections or clarify unvoiced concerns.
RESEARCH REPORTS: 1. "I have also noticed that under slight fear there is a strong tendency to yawn" (Darwin 1872:291). 2. Yawning is a displacement sign of mild conflict (Tinbergen 1951). 3. In primates, yawning appears in stress or conflict situations (Altmann 1967). 4. Yawning is seen in uneasy or aggressivechimpanzees, gorillas, gibbons, baboons, rhesus monkeys, patas monkeys, and (rarely) vervet monkeys (Lawick-Goodall 1968). 5. Yawning is a sign of stress or apathy in bonnet macaques (Rahaman and Parthasarathy 1968). 6. In humans, the yawn includes "closing of the eyes and lowering of the brows" (Brannigan and Humphries 1972:58). 7. In a tense setting, adrenaline lowers the blood's oxygen level and yawning speeds reoxygenation (Hill 1977).
Neuro-notes. Yawning is a reflexive, highly contagious act. Babies born without a brain above the midbrain (i.e., anencephalic infants) can still yawn (and stretch). Stimuli associated, e.g., with tiredness, the sight of others yawning, or social stress pass a. from higher brain centers, b. to respiratory centers in the brain-stem's medulla, and then c. to somatic motor nuclei of the trigeminal (cranial V) and facial (cranial VII) nerves. Excitement of motor fibers in the facial nerve and in the trigeminal's mandibular branch opens the mouth widely and stimulates activity in the phrenic (cervical 3, 4, and 5) nerves to the diaphragm, and intercostal (thoracic 1-12) nerves to the external intercostal muscles, causing a deep inspiration followed by deep exhalation.