A lullaby, or cradle song, is a soothing song or piece of music that is usually played for (or sung to) children. The purposes of lullabies vary. In some societies they are used to pass down cultural knowledge or tradition. In addition, lullabies are often used for the developing of communication skills, indication of emotional intent, maintenance of infants' undivided attention, modulation of infants' arousal, and regulation of behavior. Perhaps one of the most important uses of lullabies is as a sleep aid for infants. As a result, the music is often simple and repetitive. Lullabies can be found in many countries, and have existed since ancient times.
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Lullabies tend to share exaggerated melodic tendencies, including simple pitch contours, large pitch ranges, and generally higher pitch. These clarify and convey heightened emotions, usually of love or affection. When there is harmony, infants almost always prefer consonant intervals over dissonant intervals. Furthermore, if there is a sequence of dissonant intervals in a song, an infant will usually lose interest and it becomes very difficult to regain its attention. To reflect this, most lullabies contain primarily consonant intervals. Tonally, most lullabies are simple, often merely alternating tonic and dominant harmonies.
In addition to pitch tendencies, lullabies share several structural similarities. The most frequent tendencies are intermittent repetitions and long pauses between sections. This dilutes the rate of material and appeals to infants' slower capacity for processing music.
Rhythmically, there are shared patterns. Lullabies are usually in triple meter or 6/8 time, giving them a "characteristic swinging or rocking motion."  This mimics the movement a baby experiences in the womb as a mother moves. In addition, infants' preference for rhythm shares a strong connection with what they hear when they are bounced, and even their own body movements. The tempos of lullabies tend to be generally slow, and the utterances are short. Again, this aids in the infant's processing of the song.
Lullabies almost never have instrumental accompaniments. Infants have shown a strong preference for unaccompanied lullabies over accompanied lullabies. Again, this appeals to infants' more limited ability to process information.
Lullabies are often used for their soothing nature, even for non-infants. One study found lullabies to be the most successful type of music or sound for relieving stress and improving the overall psychological health of pregnant women.
These characteristics tend to be consistent across cultures. It was found that adults of various cultural backgrounds could recognize and identify lullabies without knowing the cultural context of the song. Infants have shown a strong preferences for songs with these qualities.:19
Lullabies are often used to pass down or strengthen the cultural roles and practices. In an observation of the setting of lullabies in Albanian culture, lullabies tended to be paired with the rocking of the child in a cradle. This is reflected in the swinging rhythmicity of the music. In addition to serving as a cultural symbol of the infant's familial status, the cradle's presence during the singing of lullabies helps the infant associate lullabies with falling asleep and waking up.
Studies conducted by Dr. Jeffery Perlman, chief of newborn medicine at New York-Presbyterian Hospital's Komansky Center for Children's Health, find that gentle music therapy not only slows down the heart rate of prematurely delivered infants but also helps them feed and sleep better. This helps them gain weight and speeds their recovery. A study published in May 2013 in the Journal of the American Academy of Pediatrics under the aegis of the Beth Israel Medical Center in New York City found that the type of music matters. Therapeutically designed "live" music - and lullabies sung in person - can influence cardiac and respiratory function. Another study published in February 2011 in Arts in Psychotherapy by Jayne M. Standley of the National Institute for Infant and Child Medical Music Therapy at Florida State University suggests that babies who receive this kind of therapy leave the hospital sooner.
Additional research by Jayne M. Standley has demonstrated that the physiological responses of prematurely delivered infants undergoing intensive care can be regulated by listening to gentle lullabies through headphones. In addition to slowing heart and respiration rates, lullabies have been associated with increased oxygen saturation levels and the possible prevention of potentially life-threatening episodes of apnea and bradycardia. Gentle music can also provide stimulation for premature infants to behave in ways that boost their development and keep them alive. Lullabies can serve as a low-risk source of stimulation and reinforcement for increasing nipple sucking (feeding) rates, providing infants with the nutrition they require for growth and development. Lullabies are thus associated with encouraging the rapid development of the neurological system and with a shorter length of hospitalization.
More recent research has shown that lullabies sung live can have beneficial effects on physiological functioning and development in premature infants. The live element of a slow, repetitive entrained rhythm can regulate sucking behavior. Infants have a natural tendency to entrain to the sounds that surround them. Beat perception begins during fetal development in the womb and infants are born with an innate musical preference. The element of live breathing sounds can regulate infant heart rate, quiet-alert states, and sleep. Live lullabies can also enhance parent-child bonding, thus decreasing parental stress associated with the intensive care. In short, live lullabies sung by music therapists induce relaxation, rest, comfort, and optimal growth and development.
Many lullabies, regardless of the meaning of their words, possess a peaceful hypnotic quality. Others are mournful or dark, like a lament. The Gaelic lullaby "Ba, Ba, Mo Leanabh Beag" was written in 1848 during the potato famine, which caused much hardship in the Scottish Highlands. The song mentions, soft potatoes, the mother's situation, and her fears for her child. In the 1920s, poet Federico García Lorca studied Spanish lullabies and noted the "poetic character" and "depth of sadness" of many of them. Lorca's theory was that a large part of the function of the lullaby is to help a mother vocalize her worries and concerns. In short, they also serve as therapy for the mother.
Combined with lament, lullaby can have "restorative resounding" properties for hospice inpatients and their families. Lullabies typically soothe people through the awake/sleep transition, and similarly can soothe people through the life/death transition. Music therapists have called these tunes "lullaments", that which sustain the spirit, support psychological structure, and enable resilience during times of vulnerability to the effects of adversity. Lullaments are music-contextualized expressions of attachment and detachment, sadness/tears and happiness/laughter, privilege and loss, nurturance and grief, deterioration, stasis and moving forward.
Many Christmas carols are designed as lullabies for the infant Jesus, the most famous of them being "Silent Night". "Hush Little Baby" has been observed cross-culturally and is known to have a natural capacity for soothing and energizing infants, as well as nurturing caregiving bonds.: 216
Much research has been generated on the role of lullabies in nurturing caregiving bonds between mother and child. Mothers who sing lullabies to their infants engage in a bonding activity that actually alters the underlying neural structure of the infant brain such that the infant becomes "tuned" into music and its association with parental affiliation.:217 In one Taiwanese study of Kangaroo Care, a technique practiced on newborn infants in which a mother holds her child tightly against her chest, it was demonstrated that infant-mother dyads who listened to their choice of lullaby were associated with more quiet sleep states and less occurrence of crying by the infant and were also associated with significantly lower maternal anxiety, than those dyads who did not listen to lullabies. The therapeutic effect of lullabies can thus have a strong impact on calming anxieties and nurturing bonds, which is especially important with premature and fragile infants.
Lullabies written by established classical composers are often given the form-name berceuse, which is French for lullaby, or cradle song. The most famous lullaby is the one by Johannes Brahms ("Wiegenlied", 1868). While there has been no confirmation, there are many strong arguments that Brahms suffered from a sleep disorder known as sleep apnea. It is speculated (based on lullabies' utility as a sleep aid) that this was part of his inspiration for composing "Wiegenlied." 
Chopin's "Berceuse" is a composition for solo piano. Other famous examples of the genre include Maurice Ravel's Berceuse sur le nom de Gabriel Fauré for violin and piano; the Berceuse élégiaque by Ferruccio Busoni; the "Berceuse" from the opera Jocelyn by Benjamin Godard; the "Berceuse" by Igor Stravinsky which is featured in the Firebird ballet, and Lullaby for String Quartet by George Gershwin. The English composer Nicholas Maw's orchestral nocturne, The World in the Evening, is subtitled "lullaby for large orchestra". German composer's Paul Graener last movement of his suite From The Realm of Pan is entitled "Pan sings the world a lullaby". American composer's Michael Glenn Williams "Berceuse for Solo Piano" uses an ostinato similar to Chopin's but in a 21st-century harmonic context.
"Dorme neném" (Sleep Little Baby) is sung all over the country and includes a reference to "Cuca", a folk character very feared by children.
In Hindi and in many Indian languages, the lullaby is called "Lori". Mostly, lullabies are sung in folk languages. Lullabies have been also an integral part of Indian cinema. Many lullabies were written and composed in the fifties, such as:
In the Malayalam language, there is a rich collection of traditional lullabies, known as "tharaattu Pattu". One of the most famous is "Omanathinkal Kidavo", written and composed by poet lyricist Iravi Varman Thampi who is widely known as Irayimman Thampi. This lullaby was written for the queen of Travancore to sing to her son young prince Swathi Thirunal, who later became the king and a famous musician (composed many Keerthanas in a Ragaa Dheerasankarabharanam commonly known as Sankarabharanam).
In the Odia language, a lullaby is called a Nanabaya gita. A book in the same name by Nanda Kishore bal that was published in two volumes in 1934 is a major compilation of the known lullabies in the language.
In Telugu language, a lullaby is called a "Jola" or "Jola pata". A famous Telugu lullaby is "jo achuthaa nanda jo jo mukunda".
In the Tamil language, a lullaby is called a thaalattu (thal means "tongue"). A melodious sound is created by frequent movement of the tongue at the beginning of the song.
In the Philippines, the song is known as the oyayi. The province of Batangas has a very specialized form of lullaby known as the huluna. Though only composed of simple words, it is notable for being very difficult to sing, due to the lengthy melismas. Like many traditional songs from Spain, it is full of fioriture yet unlike many of the western type songs, it has no time signature.
In Vietnamese, lullabies are called "bài hát ru". One famous Vietnamese lullaby is the song, "?u ? ví d?u". Vietnamese lullabies are hard to sing because of their extended melismas. The lullabies usually include pastoral scenes of villages, bamboo bridges, rice fields, farming, and meals made by a mother. They usually have a melancholy tone.
"Nina Bobo" is from Indonesia.
Many medieval English verses associated with the birth of Jesus take the form of a lullaby, including "Lullay, my liking, my dere son, my sweting" and may be versions of contemporary lullabies. However, most of those used today date from the seventeenth century onwards, and some of the best known English-language lullabies originate from the US. Notable English language lullabies include "Bye, baby Bunting", "Scottish Lullaby", "Suo Gân" (Welsh Lullaby), and "Hush, Little Baby".
There are many lullabies in Scottish song tradition, with well-known examples in Scottish Gaelic, Scots and English. They include songs which express emotions other than affection for the child - notably "Griogal Cridhe", which commemorates the beheading of Gregor Roy MacGregor by his father-in-law, Campbell of Glenlyon and brother-in-law in 1570 and "Hishie Ba" which may refer to a gang assault. A number of traditional lullabies also express social issues and this has been continued in modern lullaby writing in Scotland, notably Jim MacLean's "Smile in Your Sleep (also known as "Hush, Hush, Time to Be Sleeping"), Matt McGinn's "Miner's Lullaby" (also known as "Coorie Doon") and Karine Polwart's "Baleerie Baloo". Christina Stewart's kist o dreams project provides a resource of over 30 Scottish lullabies, ranging from Doric Scots of the North East, to Northern Isles dialect of Shetland, Scottish Gaelic and English language examples.
"Spi, Janí?ku, spi" ("Sleep, Johny, sleep") - This playful lullaby was collected in Moravia by Franti?ek Su?il (1804-1868), a priest and an activist of Czech national revival. He collected songs in Moravia and Silesia as well as in Slavic villages in Austria. This lullaby uses a specific name of the child, Janí?ek, a familiar form of the very common male name Jan. Nonsense is employed here, as the boy is promised not only a green and a red apple but also a blue one if he falls asleep.
"Ukolébavka" ("Lullaby") - This lullaby was published in 1633 in The Informatorium of the School of Infancy by Johann Amos Comenius (1592-1670). The book is likely to be the first treatise on the development and educating infants and children up to six in the family. Comenius stressed among other things the necessity of sensory and emotional stimuli at an early age. Thus, he included for mothers and nurses the Czech text and the score of the originally German lullaby by 16th century preacher Mathesius.
"Hajej, m?j andílku" ("Sleep, My Little Angel") - This is one of the most melodious Czech lullabies, first collected by Karel Jaromír Erben (1811-1870), Czech romantic writer, poet and collector of Czech folk songs and fairy tales. The text refers specifically to the mother rocking her baby.
"Halí, dít?" ("Hullee, baby") - This lullaby was collected by Franti?ek Barto? (1837-1906), pedagogue and ethnographer who collected Moravian songs. The second line says the carer will leave after the child falls asleep, but in the third line we learn that only to the garden in the valley to pick raspberries.
"Halaj, belaj, malu?ký" ("Sleep, Sleep, Little One") - This lullaby is from the east of Moravia, where the dialect is influenced by the Slovak language, and also folk songs are similar to the Slovak ones from across the border. A boy is promised the essential food for infants, ka?i?ka, a smooth mixture made of milk and flour.
"Elefantens vuggevise" ("The Elephant's Lullaby") - This lullaby is considered one of the most popular lullabies in Denmark. Using exotic animals as theme, the lyrics are simple and easily understood by a child. It was made politically correct in the 1990s: The word negerdreng (Negro boy) was changed to kokosnød (coconut). The song was written in 1948 by the Danish writer and poet Harald H. Lund with music composed by writer-musician Mogens Jermiin Nissen (1906-72).
"Godnatsang" ("Goodnight Song") - This is a popular lullaby that was composed (lyrics and music) by Sigurd Barrett (born 1967), pianist, composer and host of a children's TV programme in Denmark, and fellow musician Steen Nikolaj Hansen. Sigurd usually sings this song at the end of his children's show. This lullaby has sleeping time as theme: The day is over and we must sleep and rest so we will be fresh again in the morning.
"Mues sang få Hansemand" ("Mother's Song to Little Hans") - This lullaby originated from south Jutland and is very old (year of composition is unknown). It is not well known in Denmark. This may, in part, be due to the fact that it was written in Jutlandic dialect. The lyrics were written by Marie Thulesen (1878-1924) with music by the Danish musician Oluf Ring (1884-1946).
"Jeg vil tælle stjernerne" ("I Will Count the Stars") - This lullaby was written in 1951 by the Danish poet and writer Halfdan Rasmussen (1915-2002). Rasmussen had written numerous rhymes and jingles, some of which are still being used in Danish beginner classes in public schools (e.g. the picture book "Halfdans ABC"). This lullaby's music was composed by Hans Dalgaard (1919-81). The song is a simple story of a child who tries to count the stars with his/her fingers and toes.
"Slaap kindje slaap" - The text is mostly chosen for its rhyme. Sleep, little child, sleep. Outside a sheep is walking. A sheep with white feet, it drinks its milk so sweet.
"Maantje tuurt, maantje gluurt" - Older Dutch lullaby. Look the moon peeps and spies through the window. Have the children already gone to bed? Yes moon, they're lying in bed. Good, tomorrow will be a new day of playing and learning.
"Suja suja kindje" - The child is spoken to. Is your stomach aching or do you have cold feet? We will make a fire, make porridge. The cradle is rocking.
"Suze Naanje, ik waige die" - Also the child is spoken to in this lullaby. I rock you, but if you were older I would slap you. The language is Gronings dialect.
"Der Mond ist aufgegangen" (German for "The moon has risen") and "Weißt du, wie viel Sternlein stehen" (German for "Do you know how many stars are there?") are widely known since the 18th and 19th century.
"Bayu Bayushki Bayu" is a very old lullaby based on Russian folklore and beliefs. It has many different versions with different lyrics as it's a part of an ancient oral tradition where stories, rhymes and songs were told and sung at bedtime and rarely were written down. But there are always two essential elements in this song:
1) the phrase "Bayu-bayushki-bayu" which might be translated from an ancient Slavic as "hush, little baby";
2) the wolf, who might be the main evil character or the child's guardian depending on the lullaby's version.
"Hine E Hine" is from New Zealand.