The ability of human newborns to
imitate modeled facial expressions and gestures
has attracted considerable and sometimes
critical attention from a wide range of
behavioral scientists (e.g., Field, Woodson,
Greenberg, & Cohen, 1982; Meltzoff &
Moore, 1977, 1983). Although there seems to be
an increasing acknowledgement that some type of
infant imitative capacity does exist, there is
little agreement about the range of imitative
acts (see, e.g., Field et al., 1983; Kaitz,
Meschulach-Sarfaty, Auerbach, & Eidelman,
1988) or the underlying perceptualcognitive
mechanism (see, e.g., Jacobson & Kagan,
1979; Kaitz et al., 1988; Masters, 1979;
Meltzoff & Moore, 1977, 1979, 1983). Tongue
protrusion by an infant in response to a like
gesture performed by an adult model is a
frequently mentioned "imitative" act. Meltzoff
and Moore (1977, 1983) suggest that this
behavior is accomplished by the infant's
relating proprioceptive motor information about
its own unseen body movements to its
representation of the visually perceived model.
However, Kaitz et al. (1988) and others
(Jacobson, 1979; Jacobson & Kagan, 1979;
Masters, 1979) caution that such behavior may
not be true imitation, because this tenn implies
the involvement of a complex intermodal matching
process (as suggested by Meltzoff & Moore,
1977). Instead, they suggest that the action of
the model may trigger an involuntary movement of
the infant that only mimicks imitation. For
example, the apparent imitation may be an
ethological fixed action pattern (tongue
protrusion by the infant) that is "released"
(evoked) by a "sign stimulus" (tongue protrusion
by the model) (Kaitz et al., 1988). Although too
little is known about the production of infant
facial expressions and gestures to evaluate the
releasing stimulus hypothesis, there is indeed a
precedent for a facial. pseudoimitative,
releasing process in adults.
Contagious yawning involves the release of a
fixed action pattern (the yawn),by a sign
stimulus. (the observed yawn) (Provine. 1986).
Yawning is a common behavior easily studied in
adults, who are more readily available,
cooperative subjects than newboms. Adults can
also introspect and verbally report their
experiences. Although the study of contagious
yawning cannot directly test hypotheses about
behavior such as infant tongue protrusion, it
can teach us about released behavior and its
relevance to the problem of infant imitation.
Contagious yawning also provides an interesting
and always reliable classroom demonstration of
released behavior that can be part of
discussions of either infant imitation or human
ethology.
Anyone who has yawned in response to observed
yawns has experienced the triggering of a facial
expression (the yawn) by a releasing stimulus
(the observed yawn). Such yawn-evoked yawns are
not the result of a conscious desire to imitate
the yawner. An observed yawn initiates a series
of apparently automatic neurobehavioral events
that culminate in a yawn in the observer. The
contagion of yawning has been confirmed
experimentally with college aged subjects
(Provine, 1986). Visually observed yawns are
potent yawn-producing stimuli. Most subjects (55
%) viewing a 5-min long series of 30 yawns
yawned within 5 mn of viewing the first yawn.The
latency of the evoked yawns was rather long and
variable, ranging from seconds up to minutes;
fixed action patterns are not released with the
reliability and short and regular latencies
usually associated with reflexes. Nonvisual
stimuli are also effective in evoking, yawns.
Even reading about or thinking about yawning
produces either yawns or the temptation to yawn
in most subjects. The wide variety and potency
of yawn-producing stimuli contributes to the
contagion of yawning.
Because yawning is easy to produce (many
readers may already be yawning), it provides a
convenient demonstration of the fixedness of a
fixed action pattern. Typical yawns last about 6
sec (durations range from about 3 to 10 sec or
more), and individual differences in yawn
duration are maintained for at least several
weeks (Provine,1986). This stability in duration
is consistent with the property of typical
intensity, a characteristic of ethological fixed
action patterns. Fractional yawns are rarely
produced. Once a yawn is initiated, it goes to
completion. Everyone is familiar with the
difficulty of stifling a yawn. The route of
inhalation during the first phase of a yawn is
also highly stereotyped. In contrast to normal
breathing, which can be done through either the
nose or mouth, it is difficult, if not
impossible. for most people to seal their lips
and perform satisfactory yawns by inhaling
through their noses (Provine. Tate, &
Geldmacher, 1987). The characteristic gaping of
the jaw is another fixed component of the yawn.
Most people are not able to produce a satisfying
yawn with clenched teeth, although inhalation
and exhalation can be performed through the
teeth (Provine. 1986).
This commentary has focused on contagious
yawning as a precedent for facial imitation and
as an example of a released fixed action
pattern, but the development of contagious
yawning is itself worthy of study. Although
yawning is performed throughout the lifespan
(Gesell, 1928) and may be present as early as 11
weeks after conception (DeVries, Visser, &
Prechtl, 1982), the development of contagious
yawning has not been studied systematically. One
of the rare references to the topic is the
observation of 3 children that led Piaget (
1951) to conclude that yawning becomes
contagious only during the second year. If
subsequent research confirms this chronology,
the relaesing mechanism that triggers contagious
yawns develops and becomes active long after the
motor pattern generator for yawning. The very
early development of yawning in the human embryo
suggests that the motor act has a much much more
ancient phylogenetic origin than the releasing
mechanism. which develops postnatally. This
phylogenetic sequence accords with the
performance of the yawning act but not with
contagious yawning by most vertebrates (Provine,
1986). The yawning act probably evolved in early
vertebrates as a homeostatic response to one or
several yet to be defined physiological states.
Contagious yawning apparently evolved recently,
as a mechanism for coordinating the behavioral
and perhaps the physiological state of a group
(Provine & Hamernik. 1986, Provine.
Hamernik. & Curchack. 1987).
Because yawns are triggered by visually
observed yawns, yawning can be used to
behaviorally assay the yawn-evoking potency of
various facial features (Provine,1988). Thus
used, studies of yawning and perhaps infant
tongue protrusion and other presumed examples of
facial imitation join those of prosopagnosia
(face nonrecogni-tion) in brain-damaged humans
(Meadows. 1974; Whiteley & Warrington. 1977)
and of face-specific neurons in monkeys (Bruce,
Desimone, & Gross. 198 1; Parrett. Mistlin,
& Chitty. 1987; Pairett. Rolls. &
Caan,1982) and sheep (Kendrik & Baldwin.
1987), which suggest that special neural
mechanisms may be involved inthe detection and
processing og information about faces. Research
on contagious yawning tongue protrusion and
other potential examples of released behaviour
(eg Eibesfeldt, 1975) should be assigned a high
priority by students of human behavior
development. Such analyses contribute to our
understanding of processes central to both human
development and cognitive neuroscience.
Yawning,
Yielding, and Yearning to Yawn. Cialdini RB,
McPeek RW.
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