Social interaction is associated with changes in infants’ motor activity

Figures & data

Table 1 Detailed description of the seven episodes to which the infants were exposed, according to partner and context

No.	Partner	Context	Description
1	Mother	Silent distant	The mother sits at a table reading a magazine about 2 m from her infant
2	Mother	Singing close	The mother comes close to the child and sings a play song with hand movements. This song (Ainsi font font font les petites marionettes) is one of the best known in France
3	Mother	Singing distant	The mother sits at the same table (about 2 m away) and sings the same play song, without any hand movements
4	Infant alone		The infant is left alone in the room. The mother is hidden behind a screen
5	Stranger	Silent distant	The stranger sits at the table (about 2 m away) reading a magazine
6	Stranger	Singing close	The stranger comes close to the child and sings the play song with the hand movements
7	Stranger	Singing distant	The stranger sits at the table (about 2 m away) and sings the play song without any hand movements

Each episode lasted 45 s.

Fig. 1 Video Analyser interface. In the present study, circle-shaped markers were positioned frame by frame on the child's nose and tip of the left toe. Graphs illustrated changes in the position of these landmarks during an 8-s sequence (5 Hz) in the middle of the interaction episode.

Fig. 2 Mean values and standard deviations for the infants’ overall activity according to context and partner. The thick black line indicates the baseline value when the infants were left alone in the room.

Fig. 3 Mean values and standard deviations for the mean velocity (left) and utilization distribution (right) of the nose marker in the sagittal plane according to context and partner. The thick black line indicates the baseline value when the infants were left alone in the room.

Fig. 4 Mean values and standard deviations for the mean velocity (left) and utilization distribution (right) of the toe marker in the sagittal plane according to context and partner. The thick black line indicates the baseline value when the infants were left alone in the room.

Table 2 Mean correlation coefficient (standard deviation) according to context and partner

	Mother	Stranger
Alone	0.07 (0.22)
Silent	0.08 (0.15)	0.20 (0.20)
Singing distant	0.13 (0.27)	0.01 (0.12)
Singing close	0.26 (0.30)	0.20 (0.16)

Table 3 Partial eta-squared statistics for each variable and each comparison

Variable	Partner	Context	Partner×context
Overall activity	0.18	0.38**	0.37*
Face–velocity	0.36*	0.21	0.14
Face–utilization distribution	0.07	0.53***	0.12
Foot–velocity	0.11	0.26*	0.10
Foot–utilization distribution	0.01	0.17	0.29*
Face–foot correlation	0.03	0.35*	0.18

*p<0.05. **p<0.01. ***p<0.005.