Origins of smile and laughter: a preliminary study.
To present fundamental data, spontaneous smiles and spontaneous laughs (smiles accompanied by vocal sounds) were cross-sectionally observed in 10 newborn infants and longitudinally observed in six infants. Unilateral spontaneous smiles were more common than bilateral smiles in neonates, but by 2 months almost all spontaneous smiles were bilateral. All spontaneous laughs were bilateral. "Spontaneous smile" and "Spontaneous laugh" might be different behaviors from the beginning.
Kawakami
Kiyobumi
K
University of the Sacred Heart, 4-3-1, Hiroo, Shibuya-ku, Tokyo 150-8938, Japan. kawakami@u-sacred-heart.ac.jp
Takai-Kawakami
Kiyoko
K
Tomonaga
Masaki
M
Suzuki
Juri
J
Kusaka
Tomiyo
T
Okai
Takashi
T
D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007845:Laughter / Q000502:physiology*; D008297:Male; D012904:Smiling / Q000502:physiology*; D013060:Speech