What's in a Kiss? Spatial Experience Shapes Directional Bias During Kissing

One of the less-known functional asymmetries in humans is the rightward head-turning bias, in which infants spend more time turning their head to the right, rather than to the left. Observational studies showed that this asymmetry disappears around the age of 3 months. Recently, an intriguing observation found a similar rightward head-turning bias during kissing, apparently indicating that the early head-motor bias persists into adulthood. Here we challenge the theory of the innate head-turning bias in adults during lip kissing, showing by means of behavioral and observational studies that the direction of the bias is culturally dependent. Moreover, we suggest that the head-turning bias during kissing is an acquired behavioral asymmetry, probably shaped by spatial experience within cultural habits (i. e., reading direction), rather than reflecting pre-wired hemispherical lateral asymmetry.