Table 6. RSA, respiration, and heart rate across Still-Face Test episodes controlled for physical activity: Linear mixed model overall F tests (df = 2 or 4, 50.0 to 67.7), time-varying covariate activity effect F-tests (df = 1, 25.7 to 77.8) and t-tests (df = 52.4 to 77.7) testing changes from Play to Still-Face episode 1 and 2.

	Overall effect		P vs. SF1		P vs. SF2		Activity
	F	p	t	p	t	p	F	p
Test 1 (n = 23)
RSA (ms)	0.17	.844	−0.53	.599			0.73	.397
logRSA/VTc (log ms/mL)	9.78	.001	−3.37	.001			0.42	.518
TTOT (s)	1.10	.341	1.46	.149			0.91	.345
VT (mL)	6.36	.004	1.32	.193			1.23	.273
HR (b/min)	8.67	.001	0.93	.359			14.18	.001
Test 1 and 2 (n = 16)
RSA (ms)	1.46	.226	−0.25	.803	−1.59	.118	4.28	.043
logRSA/VTc (log ms/mL)	6.93	.001	−2.67	.009	−5.01	.001	0.23	.882
TTOT (s)	5.56	.001	1.60	.115	3.97	.001	1.80	.184
VT (mL)	5.06	.001	1.42	.162	3.05	.003	1.21	.276
HR (b/min)	3.83	.007	1.03	.309	2.06	.044	7.76	.007

Note: V_T = tidal volume; RSA = respiratory sinus arrhythmia; T_TOT = total respiratory cycle time; HR = heart rate; RSA/V_T = RSA normalized by V_T; c = adjusted.

for total respiratory cycle time; logRSA = logarithm(RSA+1); logRSA/V_T = logarithm(RSA/V_T)+1.