The baby sleeps more soundly in the cradle, which is definitely not our adult imagination. The researchers confirmed the soothing effect of shaking on the baby, and also found that the degree of emotional stability of the baby was not only related to the amplitude and frequency of the shaking, but also closely related to the maximum acceleration when shaking.
This is the crib of the infant jesus now in the collection of the Metropolitan Museum of Art, this miniature wooden cradle is 35.4 cm long, 28.9 cm wide and 18.4 cm high, which is a popular religious object in the fifteenth century, and this cradle dates back to brabant in south Holland in the 15th century. (Source: metmuseum.org)
Written by | Anjie Cao (Carnegie Mellon University)
Every time I walk by the baby shop, I always cast a laser-like look of envy and hatred. All kinds of small things in it, whether it is tableware or toys, are exquisitely and cutely made, which makes me sigh unceasingly, eager to quickly pull over a clerk and ask: Why can't these things be made into an adult model?!
Of the many things in the baby store, the cradle I want most is the cradle. Don't hide from you, I have searched countless times on Taobao, "adult cradle", "oversized cradle", "cradle size customization" and so on, but so far nothing has been received. Sometimes when I lie in bed, I can't help but imagine an electronic cradle that is long enough and large enough: it can be timed, the amplitude and frequency of the shake can be adjusted; every day before going to bed, I gently turn on the switch, click- "Shake, shake, shake to Grandma's Bridge..." Definitely dipped in pillows. After all, when the baby sleeps in the cradle, he always sleeps so soundly that it is extremely enviable.
The mystery of the cradle
The baby sleeps more soundly in the cradle, which is definitely not our adult imagination. In the 1970s, psychologists David Pederson and Dick Ter vrugt conducted a series of experiments to study: What amplitude and frequency of exercise can more effectively soothe a baby's emotions? They designed an aluminum cradle with a base that could be used to adjust the amplitude and frequency of the cradle's vertical swing.
They then recruited dozens of two-month-old babies locally, had seven female and seven male observers assess how well the babies were rocked around in the cradle, and gave their babies a scale of behavior every fifteen seconds: the score ranged from 1 to 6, and the higher the score, the higher the activity. 1 point corresponds to quiet sleep and 6 points corresponds to extremly agitated (bridger, birns & blank, 1965).
These babies were never shaken in vain: the researchers confirmed the soothing effect of shaking on the baby, and also found that the degree of emotional stability of the baby was not only related to the amplitude and frequency of the shaking, but also closely related to the maximum acceleration during shaking. The greater the maximum acceleration when shaking, the more stable your baby's mood becomes.
The y coordinate in this graph is the baby's activity score, while the abscissa is the calculated maximum acceleration (gmax = [(2×pi×f)2×a] / 32, gmax is the maximum acceleration, f is the frequency, and a is the oscillation amplitude). The data points scattered in the plot are the frequency (laps/minute) in front of the colon and the oscillation amplitude (inches) after the colon. (Source: Pederson & Vrugt, 1973)
But why does your baby sleep better when shaken? In fact, not only the cradle shakes, but also a small amount of exercise has the effect of soothing the baby and helping the baby sleep. This movement is also known by developmental psychologists as vestibular stimulation.
Survival advantages for well-behaved babies
The vestibular system is one of the earliest developed sensory systems in humans (humphrey, 1965). The vestibular system consists of two parts: the semicircular canal and the otolith. Among them, the semicircular canal is mainly responsible for feeling the rotational motion, and the otolith is responsible for feeling the gravity in the vertical direction. The vestibular system is located in our inner ear, and sometimes patients with otitis media experience symptoms of dizziness because inflammation affects the processing of sensory information by the vestibular system of the inner ear.
The orange part is the outer ear, the pink part is the middle ear, and the blue part is the inner ear. Our vestibular system and cochlea (cochlea) together make up the inner ear. (Source: britannica.com)
The vestibular system has a long evolutionary history, and it exists in most mammals. Some parents may find that if their baby starts to cry, hold the baby up and walk around, pat it, the baby's mood will settle down; if the baby in the cradle is crying, gently shaking the cradle can also make the baby stop crying. However, although it is also the soothing effect of vestibular stimulation, the mother's hug and pat also provides tactile stimulation.
In 2013, a group of scientists from Japan simultaneously studied and compared maternal and infant interactions between humans and mice. This calming effect of stimulation of the vestibular system is also present in mother mice and baby mice. They found that when the human mother stood up and began to walk around holding the baby, the crying baby would stop crying, the autonomous movement would be reduced, and the heart rate would be correspondingly reduced. Similarly, when a baby mouse is picked up by the mother and walked around, the baby mouse will remain motionless and the heart rate will decrease (esposito et al., 2013).
Why does vestibular stimulation have a soothing effect? From the perspective of evolution, such a soothing effect will bring about a considerable survival advantage. Many mammals, including humans, rely on their mothers for a long time after birth. If there is any dangerous situation and the mother has to urgently transfer the baby, a quiet and unmoving baby definitely has a greater chance of survival than a baby who cries and stomps on his hands and feet. In the 2013 paper, the authors argue that this also explains both Pederson and VRUGT's findings: the higher the frequency and amplitude of the wobble, the faster the mother's pace and the greater the range of motion, which means that the more urgent the situation, the quieter the baby is under such exercise.
In addition to being carried around by the mother, another of the more common vestibular irritations is to take a car. I've heard of some dads who don't know how to coax their crying babies to put them in a car seat and drive around in circles. What is even more exaggerated is that a famous car company has also launched a cradle, claiming to completely simulate the baby's environment in the car: slight shaking, the faint sound of the engine in the background, and even the street lights that constantly skim over the windows. However, it is worth pointing out that some people think that such a high-tech cradle does not actually help to cultivate healthy sleep habits for babies. Babies may develop a dependence on these sounds, light, and motor stimuli, which do more harm than good in the long run.
(Image source network, screenshot from the company's promotional video.) In order to avoid the suspicion of advertising, I will not say which company it is~)
Then again, the reason is so, I still can't help but plant a grass for this little cradle in my heart, and I hope that it will quickly launch an adult version. But on second thought, it's sound, it's light, it's shaking again, hey, what else am I spending on it — isn't it a reason for me to buy a ticket for a sleeper train!
Resources
[1] bridger, w. h., birns, b. m., & blank, m. (1965). a comparison of behavioral ratings and heart rate measurements in human neonates. psychosomatic medicine.
[2] humphrey, t. (1965). the embryologic differentiation of the vestibular nuclei in man correlated with functional devlelopment. in international symposium on vestibular and occular problems. society of vestibular research. university of tokyo.
[3] pederson, d. r., & vrugt, d. t. (1973). the influence of amplitude and frequency of vestibular stimulation on the activity of two-month-old infants. child development, 122-128.
[4] esposito, g., yoshida, s., ohnishi, r., et al. (2013). infant calming responses during maternal carrying in humans and mice. current biology, 23(9), 739-745.
This article is co-produced by "Brain Man Speech" and "Mr. Sai"