Table 2. Mean proportion for whole observation session and standard division (SD) of 6 behavioral indices at 4, 9, 18, 30, 42 month.

month	Infant			Mother
	gaze at Mother	gaze at toy	vocalize	gaze at Infant	gaze at toy	vocalize
	Mean (SD)	Mean (SD)	Mean (SD)	Mean (SD)	Mean (SD)	Mean (SD)
4	0.48 (0.252)	0.69 (0.356)	0.13 (0.185)	0.96 (0.085)	0.34 (0.254)	0.90 (0.136)
9	0.33 (0.204)	0.85 (0.277)	0.12 (0.155)	0.94 (0.070)	0.64 (0.271)	0.88 (0.132)
18	0.22 (0.185)	0.68 (0.328)	0.28 (0.209)	0.60 (0.246)	0.64 (0.323)	0.89 (0.133)
30	0.21 (0.171)	0.85 (0.178)	0.53 (0.238)	0.53 (0.210)	0.78 (0.230)	0.90 (0.124)
42	0.28 (0.206)	0.86 (0.161)	0.61 (0.252)	0.60 (0.192)	0.81 (0.192)	0.91 (0.113)