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Le bâillement, du réflexe à la pathologie
Le bâillement : de l'éthologie à la médecine clinique
Le bâillement : phylogenèse, éthologie, nosogénie
 Le bâillement : un comportement universel
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Yawning: its cycle, its role
Warum gähnen wir ?
Fetal yawning assessed by 3D and 4D sonography
Le bâillement foetal
Le bâillement, du réflexe à la pathologie
Le bâillement : de l'éthologie à la médecine clinique
Le bâillement : phylogenèse, éthologie, nosogénie
 Le bâillement : un comportement universel
La parakinésie brachiale oscitante
Yawning: its cycle, its role
Warum gähnen wir ?
Fetal yawning assessed by 3D and 4D sonography
Le bâillement foetal

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1 août 2010
Contagious Yawning and Laughter
Significance for Sensory Feature Detection, Motor Pattern Generation, Imitation, and the Evolution of Social Behavior
Robert R. Provine
Department of Psychology
University of Maryland Baltimore USA
Autres articles de R. Provine et R. Baenninger
Social Learning in Animals. The Roots of Culture
Ed Cécilia M. Heyes, Bennett G. Galef jr
Academic Press 1996 San Fiego. California


Contagious yawning and laughter in humans offer insights into a variety of problems in the neural, behavioral, and social sciences. Contagion is the probable response of "stimulus feature detectors" triggered specifically by yawns in the visual domain and laughs in the auditory domain (Provine, 1986, 1989b, 1992, 1996a). It does not require conscious effort for an observer to imitate a yawning or laughing person. In the language of classical ethology, these neurological stimulus detectors would be "innate releasing mechanisms" (IRMs) evolved to detect the "releasing stimuli" of yawns or laughs (Alcock, 1989; Provine, 1986, 1996a). Such stimulus feature detectors are more likely to have evolved to select the simple, stereotyped, species-typical acts of yawning or laughing than more arbitrary and variable behaviors learned during a lifetime of the individual. Because observed yawns or laughs trigger their respective neurological detectors to evoke identical acts, contagious yawning or laughter may be used to assay the activity and determine the selectivity of the underlying detection process. Contagious behavior, thus, provides a novel, noninvasive approach to the neural basis of sensory feature detection.
The study of species-typical and stereotyped yawning (Provine, 1989b) offers advantages over other approaches to the detection of faces (a visual feature) that rely on neuropsychological studies of rare clinical conditions (i.e., prosopagnosia) (Meadows, 1974; Whiteley & Warrington, 1977) or the electrophysiological recording of face-specific brain neurons in animal models (Bruce, Desimone, & Gross, 1981; Kendrick & Baldwin, 1987; Perrett, Mistlin, & Chitty, 1987; Perrett, Rolls, & Caan, 1982). In the auditory domain, the search for a detector for structurally simple, stereotypic, and species-typical laughter offers advantages over more complex and culturally varied speech (Provine, 1992, l993a, l996a). The simplicity, stereotypy, and species typicality of yawning and laughter offer similar tactical advantages in the search for motor pattern generating circuits (Provine, 1986, 1996a; Provine & Yong, 1991).
In studying contagious yawning and laughter, we move seamlessly from the neural to the social level of analysis. Yawning and laughter offer a rare opportunity to examine the neurological basis of that significant but neglected class of social behavior-contagion (Provine, 1989b; Provine, 1992). Typically, social psychologists focus on behavior learned during the life time of individuals and neglect innate or neurologically mediated social behavior. Social psychologists describe contagious-like behavior in the context of higher level processes such as "social facilitation," "conformity," "peer pressure," or "modeling," and seldom consider the possible biological roots of contagious phenomena.
Because the biologic and genetic determinants of yawning and laughter are stronger than that of many behaviors studied by social scientists, they should not be relegated to the category of "interesting footnotes." We should not segregate them from other, more familiar, social acts shaped more directly by learning and experience. A thoughtful position on such matters is offered by an expert on behavioral contingencies, B. F. Skinner (1984). When asked to respond to the challenges to operant behavior by the discovery of "biological constraints on learning," "feature detectors" in sensory systems, and "pattern generating circuits" in motor systems (Provine, 1984a), central themes of this chapter, Skinner (1984) replied "that a given species is predisposed by its genetic history to see particular stimuli in preference to others or to behave in particular ways in preference to others are facts of the same sort. A different kind of selection has been at work." In other words, the contingencies of natural selection can shape structure and behavior during phylogenesis in a way similar to the process that shapes behavior, during the life of the individual.
Contagious yawning and laughter provide insights into imitation, a common topic in this book, and a process of general behavioral significance (Piaget, 1951; Provine, 1989a). Instead of venturing into the semantic quicksands of definition, this chapter has the more modest goal of broadening the range of acts evaluated in imitation studies. Consider, for example, the controversy over the existence and nature of facial imitation by human neonates (Meltzoff & Moore, 1977, 1983). Most researchers of facial imitation suggest the involvement of high-level cognitive processes, and have not considered the precedents of contagious yawning and laughter. Although contagious behavior may not qualify as imitation as commonly defined, it is a ubiquitous, ancient form of social coupling that coexists with modern, consciously controlled social behavior (Provine, 1986, l989a, b, 1992).
This chapter describes contagious yawning and laughter and shows how these acts can be used to study a variety of issues in the neural, behavioral, and social sciences. The neuroethological approach taken here has a strong descriptive foundation. Consequently, this account begins with the description of the motor acts of yawning and laughter because, in the case of contagious behavior, the motor act is both the stimulus and the response, and defines the nature of the stimulus feature detector supporting contagion.
 robert provine
Yawns as Stereotyped Action Patterns
The word for yawning is derived from the Old English "ganien," meaning to open wide as in gape. Yawns are slow, involuntary, gaping movements of the mouth that begin with a slow inspiration of breath and end with a briefer expiration. Yawning is a behavior of the type called "fixed," "modal," or "stereotyped," by ethologists (Alcock, 1989; Provine, 1986). The term "stereotyped action pattern" will be used here to refer to such acts. Consideration of yawning will begin with a description of its duration, frequency, and intrasubject stability. These descriptions define yawning and provide baseline data necessary for later experiments.
The mean yawn duration was 5.9 ± 1.9 s (SD) for the 34 of 37 subjects who yawned at least once during the observation period (2. The formidable problem of getting subjects to yawn in the laboratory was solved by having them 'think about yawning" and record their own yawns by pushing a button at the start of a yawn and keeping it depressed until the yawn is complete. This technique avoids inhibitions associated with the well-known social sanctions against public yawning. Unless otherwise noted, this procedure was used to induce and record yawns.) (Provine, 1986). The mean duration of yawns for individual subjects ranged from 3.5 to 11.2 s. Yawning frequency of the 34 yawning subjects ranged from 1 to 76 (X = 27.5 ± 18.4) during the 30-min period of observation, an average rate of about one yawn per min. The periodicity of yawns, the onset-to-onset interyawn interval, for the 31 subjects performing at least two yawns, was 68.3 ± 33.7 s. No significant correlation was detected between yawn duration and interyawn interval, indicating that infrequent yawners did not compensate by performing long yawns and vice versa. (The significance of this finding for respiratory function is considered below.) Whatever their style, individual yawning patterns were stable. The frequency and duration of yawns performed by the same subjects during 10 min sessions separated by 1 to 3 weeks were correlated significantly.
Once a yawn is initiated, it goes to completion with the inevitability of a sneeze. Yawns are hard to stifle. The implications of this experience were examined by having subjects yawn with clenched teeth. This procedure tests for the effects of eliminating or modifying movement-produced feedback associated with the gaping component of the yawn while permitting normal respiration through the clenched teeth (Provine, 1986). The frequency and duration of normal and clenched-teeth yawns as estimated by the respiratory component were similar. Thus, the underlying motor pattern generator for yawning was able to run normally with abnormal sensory feedback. However, subjects reported that such yawns were unpleasant, did not satisfy the urge to yawn, and gave the impression of being "stuck" in midyawn. The gaping of the jaws must be performed to achieve a satisfying yawn; the respiratory component is insufficient. Try a clenched-teeth yawn yourself.
Another yawn variant is informative. Try a "nose yawn" in which your lips remain sealed and you inspire through the nose. Most subjects report being unable to perform nose yawns (Provine, Tate, & Geldmacher, 1987). Unlike normal breathing that can be done with equal facility through either the nose or mouth, yawns require inhalation through the mouth. The difficulties of performing the nose and clenched-teeth yawns suggest that the principal function of a yawn is not respiratory; deep breaths can be taken through either the clenched teeth in the clenchedteeth yawn, or the nose in the nose yawn.
The function of yawning is elusive. However, one of the most common popular explanations of yawning can be rejected. Yawning is not a response to elevated CO2 or decreased 02 in the blood or brain. Yawning by laboratory subjects was neither increased by breathing a gas mixture high in CO2 (3% or 5%), nor inhibited by breathing 100% °2 (Provine et al., 1987). (The normal composition of air is 20.95% 02, 79.02% N2 and inert gases, and .03% CO2.) However, both the CO2 and the 02 conditions increased breathing rate, providing clear evidence that they had evidence suggest that the yawn should be considered a form of stretch and that investigations of yawn function should include the correlates of stretching. (Yawning may have evolved as the facial component ofa generalized stretched response that has an added respiratory element (Provine, Hamernik, & Curchack, 1987). However, given the phylogenetic antiquity of yawning, it is also possible that stretching evolved after and may be an elaboration and caudal extension of a yawn, the primal stretch).
Although not studied systematically, there are several significant differences between yawning and stretching. There is less conscious control over yawning than stretching, yawning is more contagious than stretching, yawning has as respiratory element lacking in stretching, yawning has a greater involvement of neck and head structures than stretching, and yawning has a Valsalva-like (breath holding and "bearing down") maneuver lacking in stretching.
At present, there is much speculation, but little evidence about a function for yawning. However, yawning, like stretching, is a high-amplitude maneuver that probably has numerous consequences through the body. Each of these physiological correlates may be a "function" (i.e., have some plausible benefit). There is no evidence that yawning either increases Or decreases alertness. However, yawning is linked with some changes in behavioral states. We yawn during the transition from sleep to wakefulness, from wakefulness to sleep, and when becoming bored. The association between yawning and change in behavioral state was pointed out by fish behaviorist Arthur Myrberg (1972), who noticed that when the damselfish he studied on a reef yawned, they would soon switch from one to another class of activity. Yawning may facilitate such state transitions.
The search for a yawn function should also consider the phylogerietic antiquity of the act. Most vertebrates yawn, a fact that indicates a motor pattern generating process and perhaps at least one physiological correlate (i.e., "function") common to all yawning organisms. Additional motor components and physiological correlates may have evolved from this primal prototype.
The occurrence of yawning during the first trimester of human prenatal development opens the possibility of a role of yawning in embryogenesis. Would it not be surprising if a function of yawning is to ensure the proper articulation of the jaw joint by moving it during development? The sculpting and maintenance of developing joints is an important function of prenatal movement (Provirie, 1993b). Yawn functions noted in contemporary humans, such as opening the eustachian tube to equalize pressure in the middle ear and the ambient environment (Laskiewicz, 1953), may be secondary consequences of an act evolved in the service of some other environmental or developmental challenge.
Whatever the physiological and behavioral consequences of normal yawning, yawning is symptomatic of a wide range of pathology, including brain lesions and tumors, hemorrhage, motion sickness, chorea, and encephalitis (Graybiel & Knepton, 1976; Jurko & Andy, 1975; Barbizet, 1958; Heusner, 1946). Psychotics are reported to yawn rarely, except when suffering from organic brain syndrome (Lchmann, 1979). This intriguing observation, considered with the finding that antidopinergic agents often produce yawning, suggests that yawning may provide a metric for the pathogenesis of schizophrenia (associated with elevated dopamine levels) and a useful assay for the titration of antidopaminergic neuroleptic dosages. Lehmann (1979) notes further the old clinical observation that people suffering from acute physical illnesses never yawn when their condition is serious; a return of yawning signals convalesence. In regard to neurotransmitters, yawning is associated with cholinergic and peptidergic excitation and dopaminergic inhibition. Because yawning is stimulated by hormones (i.e., testosterone, oxytocin, ACTH, MSH) and drugs (i.e., apomorphine, piribedil, pilocarpine) with known mechanisms of action, yawning can serve as a useful, noninvasive, behavioral assay of chemical events within the brain. Clinically, yawning is therapeutic in preventing atekctasis, the collapse of alveoli, a frequent postoperative respiratory complication (Cahill, 1978).
To conclude this discussion of yawning as a motor act, it is appropriate to return to the initial ethological theme and review the properties that qualify yawning as a stereotyped action pattern (Provine, 1986).
1. Yawning is species-typical in humans, performed by all members of our species. [We do not show the higher rates of male yawning reported for more dimorphic primates (Schino & Aureli, 1989).1 Yawning is not, however, species exclusive; most vertebrates yawn (Baenninger, 1987; Deputte, 1994; Huesner, 1946).
2. Yawning is consistent in duration (average duration 6 s).
3. Yawning occurs periodically (average interyawn interval 68 s).
4. Yawning is under strong genetic control because it is already performed by embryos during the first trimester of prenatal development (DeVries, Visser, & Prechtl, 1982) and is obvious in both normal and anencephalic human newborns (Heusner, 1946; Provine, 1989a).
5. Yawns are unitary, being performed at so-called "typical intensity." Fractional (atypically short) yawns are seldom seen.
6. The amplitude and duration of yawns are independent of the amplitude of the releasing stimulus Of present). Further, once initiated, yawns go to completion with minimal influence of sensory feedback; everyone is familiar with the difficulty of trying to stifle a yawn (Provine, 1986).
7. Yawns can be "released" by witnessing yawns or yawn-related stimuli (Provine, 1986; 1989b), the basis of the contagious yawn response.
8. Yawns are complex in spatiotemporal organization and have facial, respiratory, and other components, e.g., yawns are not simple reflexes of short duration.
9. The motor components of a yawn occur in only one order and the timing of components is consistent from yawn to yawn. This stability of sequence contributes to fhe yawns unmistakable appearance, an important property for a releasing stimulus.
10. The finding that yawns are prominent in people who are waiting, or performing monotonous work (Provine & Hamernik, 1986), and of dogs on the threshold of aggression, or participating in an aversive activity, is consistent with the performance of yawns as "displacement acts" (Provine, 1986).
Given these many properties, yawning has been recognized as one of the best examples of stereotyped action pattern and releasing stimulus in humans (Alcock, 1989). Yawns are not reflexes. As traditionally understood, reflexes are simpler acts of short duration, are evoked by stimuli, have short response latencies, and have response amplitudes that are correlated with stimulus amplitudes.
Contagious Yawning
The contagiousness of yawning is legendary. Viewing, reading about, and thinking about yawning evokes yawns (Provine, 1986). Although yawning is interesting in its own right, contagious yawning is a means of assessing the yawnevoking potency of various facial features. Thus used, the search for the ethological releasing stimulus for yawns provides insights into face detection, an issue in perception and neuropsychology (Provine, 1989b). The discovery of a perceptual process activated exclusively by visually observed yawns establishes a precedent for a facial feature and/or expression detector in humans. Similar detectors may exist for facial expressions (actions) other than yawns, and for other complex visual stimuli, but their activity may be more difficult to monitor because they lack a contagious response as a behavioral assay.
A series of studies evaluated the yawn-evoking potency of various features of a yawning face (Provine, 1986, 1989b). The yawn-evoking capacity of variations in a 5-min series of 30 videotaped repetitions of a yawning face (one yawn every 10 s) were compared with each other and with a control condition of a series of 30 videotaped smiles (Provine, 1989b). Single frames of the monochrome video stimuli in midyawn or midsmile are shown in Fig. 1. The 360 subjects, 30 per stimulus condition, were instructed via videotape to observe a video monitor and to record their yawns by pressing a button.
The normal yawning face (Fig. la) was an effective stimulus, causing 16 of 30 subjects (Fig. 2, upper) to produce a total of 92 yawns (Fig. 2, lower), significantly more yawns than to the smile. The yawn-detection process was not axially specific; yawns in orientations of 90°, 180°, and 270° were as potent or nearly as potent as normal, upright, 0° yawns. The number of subjects who yawned in response to the high-contrast yawn (Fig. lb) did not differ significantly from those who yawned in response to normal-halftone yawns (Fig. la) or smiles (Fig. 1h). A tonic (still) yawn video frame of a yawner in midyawn (Fig. la) produced a number of yawners midway between, and not significantly different from that produced by normal, animate yawns or smiles.
The "no-mouth" yawn (Fig. le) was the only stimulus with a deleted feature that produced as many yawning subjects as the complete face and significantly more yawners than did the smile (Fig. 2). This initially counterintuitive and disconcerting result was, however, consistent with other data. Consider, for example, the relative ineffectiveness of the "mouth-only" yawn (Figs. le and 2). The gaping mouth, the most obvious candidate for the ethological "sign stimulus" for yawning, is not necessary to evoke contagious yawns. Instead, the yawn detector may be triggered by the overall configuration of the yawning face, perhaps being driven by cues involving the squinting of the eyes, tilting of the head, and movement of the jaw. The importance of the overall configuration and dynamic cues in the discrimination of facial expressions is reinforced by findings of Leonard, Voeller, and Kuldau (1991). In monkeys, a lack of axial and feature specificity in many facespecific neurons suggest a stimulus analysis of the sort described in the present behavioral analyses of human yawns (Bruce et al., 1981; Perrett, Mistlin, & Chitty, 1987; Perrett, Rolls, & Caan, 1982). Monkeys even have neurons specific for yawning faces. These diverse behavioral and neurophysiological results suggest common underlying processes. It is unlikely that complex neural mechanisms for similar perceptual tasks would evolve independently and have radically different principles of operation.
Determination of latencies of the contagious yawn responses provides additional information about the dynamics and nature of the underlying process (Provine, 1986). The stimulus in the latency study was the animate video of the normal yawning face described previously. As in the previous experiment, yawns were potent yawn-inducing stimuli; 23 of 42 subjects (55%) yawned during a 5-min session. Only 5 of 24 subjects (21%) yawned while viewing the control condition of a recurrent series of videotaped smiles. The proportion of subjects yawning while viewing yawning gradually increased during the 5-min session. These data are consistent with the involvement of a complex, higher order perceptual process involving polysynaptic processes; the contagious yawn mechanism is not a reflex having a short and consistent latency.
The complexity of the contagious yawn mechanism is suggested further by the ariety of nonvisual stimiIi that can evoke it. As readers may have concluded already, simply reading about yawning is sufficient to trigger yawns (Provine, 1986; Carskadon, 1991, l992):The potency of the text-induced yawning effect was tested
by comparing the yawns performed by subjects reading about yawning with yawns performed by subjects reading a control passage about hiccupping. Significantly more subjects either yawned or thought about yawning while reading about yawning than reading about hiccupping.
Most stimuli associated with yawning can evoke yawns. For example, even the sound of yawning, or thinking or reading about yawning, triggers yawns. Given the variety of potential yawn-evoking stimuli, further exploration of the range of yawn-inducing stimuli may yield diminishing returns. Although the contagious yawn is a highly mechanistic social response to yawn-related stimuli, the underlying process does not exclusively involve a detector for a narrowly defined visual stimulus. Does this mean that the "innate releasing mechanism (IRM)" of classical ethology is less selective and more modifiable in humans than in other animals? Or does the human data inform us of the true nature of released behavior as performed throughout the animal kingdom? Our subjective experience of contagious yawns may provide valuable evidence that similar released behavior in nonhumans is not as rigidly determined and selective as is often assumed.
Age of onset of visually evoked contagious yawn responses has not been established (Provine, 1989a). However, spontaneous yawning is already present by the end of the first trimester of prenatal development (DeVries et al., 1982) and is obvious in newborns. In one of the rare developmental references, Piaget (1951) suggested that yawning becomes contagious during the second year of life. Thus, the present tentative evidence suggests that contagious yawning develops after the superficially similar facial-"imitation" response reported in human neonates (Meltzoff & Moore, 1977, 1983). If subsequent research confirms this chronology, the releasing mechanism that triggers contagious yawns develops and becomes active long after the motor pattern generator for yawning.