Abstract
Yawning is contagious in human adults. While infants do not show contagious yawning, it remains unclear whether infants perceive yawning in the same manner as other facial expressions of emotion. We addressed this problem using functional near-infrared spectroscopy (fNIRS) and behavioural experiments. We confirmed behaviourally that infants could discriminate between yawning and unfamiliar mouth movements. Furthermore, we found that the hemodynamic response of infants to a yawning movement was greater than that to mouth movement, similarly to the observations in adult fMRI study. These results suggest that the neural mechanisms underlying yawning movement perception have developed in advance of the development of contagious yawning.
Highlights
Many studies have shown that contagious yawning can be observed in several mammals[1,2,3,4,5,6,7,8,9,10]
No significant main effect of age and interaction was observed (movement condition: F(1,42) = 2.78, p = 0.10, ηp2 = 0.06; age: F(2,42) = 0.00, p = 0.1, ηp2 = 0.00; interaction: F(2,42) = 1.93, p = 0.16, ηp2 = 0.08); there is no difference between movement condition and age, suggesting that the preference for yawning and mouth movement did not differ in an inverted face
The results revealed that the concentration of oxy-Hb and total-Hb increased significantly in both temporal areas during the presentation of yawning movement (for oxy-Hb: left, t(11) = 2.70, p = 0.020, d = 0.779 and right, t(11) = 2.65, p = 0.022, d = 0.766, for total-Hb: left, t(11) = 2.81, p = 0.017, d = 0.810 and right, t(11) = 3.05, p = 0.011, d = 0.880) No significant increase was observed in both temporal area during the presentation of mouth movement (for oxy-Hb: left, t(11) = −0.918,p = 0.378, d = 0.265; right, t(11) = −0.562, p = 0.585, d = 0.162; and for total-Hb: left, t(11) = 0.524,p = 0.610, d = 0.151; right, t(11) = 0.451, p = 0.660, d = 0.130)
Summary
Many studies have shown that contagious yawning can be observed in several mammals[1,2,3,4,5,6,7,8,9,10]. Nakato et al.[15] investigated view-invariant face processing in infancy using fNIRS, and found that 8-month-old infants showed greater neural activity in the posterior temporal areas in response to frontal and profile faces. These neural activations were related to the discrimination of faces. Inverted dynamic point-light displays (PLDs) depicting facial expressions of surprise to 7- to 8-month-old infants; higher activation in the right temporal area was observed only during the upright presentation of the dynamic PLDs. Nakato et al.[17] reported a higher activation in infants’ right posterior temporal area in response to the static angry faces, and in the left area to the static happy faces. Based on the above evidence, we hypothesized that the posterior temporal areas would be activated when viewing the yawning movement
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