A Within-subjects Experimental Protocol to Assess the Effects of Social Input on Infant EEG

The overall goal of this procedure is to systematically tease apart how different types of social inputs differentially relate to infant neural activation by recording infant EEG in both social and nonsocial contexts. The main advantage of this technique is the inclusion of control social and nonsocial conditions to examine effects on infant EEG of different social inputs, including language and face-to-face interaction. This method has implications for the field of developmental cognitive neuroscience, highlighting the need to consider the role of EEG recording context when assessing functional neural activation.

This method can be applied to the study of individual differences to see how EEG activity in the presented conditions varies by factors such as socioeconomic status, age, or parenting quality. We first had the idea for this paradigm when we noticed that many studies have recorded infant EEG during baselines that combine both social and nonsocial elements. It is best to conduct this experiment in an electrically shielded booth to prevent interference with the EEG signal.

Position two speakers on the ground on either side of the table, directed towards the chair. Place a tripod video camera under the table and facing up so that the infant's face will be in clear view during the experiment. Hang an opaque curtain immediately behind the table so that the experimenter can stand behind it to be hidden from the infant's view during parts of the paradigm.

Finally, place cereal, a small stuffed animal, and a rattle in the booth. Obtain informed parental consent and explain the EEG experiment and paradigm that will be used. To begin, measure the infant's head in centimeters at the widest point using a soft tape measure.

Then choose the appropriate sized EEG net and soak it in a warm electrolyte solution. Use a towel to pat off excess water to prevent bridging. Allow the parent to touch the net if interested.

Have the parent sit on the chair in the booth with the infant on their lap. Then place both hands inside the net and gently stretch the net, and lower it so that it first over the infant's head with the Cz electrode on the vertex of the head. When the net is positioned, remove both hands and tighten the chinstrap so that the net is secure.

Inspect the net for correct positioning and make adjustments as necessary. At this point, measure electrode impedance using the EEG recording software. Squeeze a few drops of electrolyte solution using pipettes on to any electrodes with poor contact.

If necessary, gently move the infant's hair, so that the electrodes are in better contact with the scalp. During the experiment, record EEG data according to manufacturer specifications. Set up the paradigm to present a series of 10 color photographs of objects on the monitors for 13.0-14.5 seconds at variable interstimulus intervals of 0.5-2.0 seconds.

Display the same photograph on both screens throughout the protocol and present a white screen along with a bell sound to signal the start of each block. Administer blocks as follows:Social engagement, nonsocial, joint attention, language-only, joint attention, nonsocial, social engagement, and language-only. These conditions are designed to tease apart the effects of social input on infant EEG.

See the manuscript accompanying this video for details. It is critical to use the same tone of voice and the same positive affect throughout the paradigm and with all participants. The social engagement and joint attention conditions should be clearly differentiated.

Ensure that no joint attention behaviors are present during the social engagement condition by maintaining the infant's attention on the experimenter's face and not following the infant's gaze. For social engagement, lean on the table between the computer monitors to be face-to-face with the infant. Maintain the infant's attention so that they do not focus on the screens by singing children's songs with hand motions and playing peek-a-boo.

Next, for the nonsocial condition, hide behind the curtain and remain silent throughout the entire block of stimulus presentation. Then, for the joint attention condition, lean on the table between the computer monitors to be face-to-face with the infant. Direct the infant's attention to the pictures while following a specified script of utterances and pointing directions for each trial.

At the start of each trial, make eye contact with the infant and continue bids for attention until the infant looks. Then, turn in the pre-specified direction to look at the appropriate screen and point to the picture while simultaneously saying the utterance for each trial. Continue to alternate gaze between the picture and the infant's face until the trial is over.

Finally, for the language-only condition, Go behind the curtain while commenting on the pictures, also following the specified utterances. Continue to follow the pre-specified sequence of conditions until the experiment is completed. For data analysis, use a repeated measure strategy, first including the nonsocial and joint attention conditions in the model.

Then repeat the model twice, first including the language-only condition, to test whether a language input explains differences between nonsocial and joint attention conditions. Second, include the social engagement condition to test whether face-to-face interaction explains differences between the nonsocial and joint attention conditions. In this sample of 12-month-old infants, overall 4-6 Hz power was lower in the joint attention condition, indexing greater neural activation compared to all other conditions.

Next, comparing EEG power by condition and region, 4-6 Hz power in the frontal and parietal regions was lower in the joint attention condition compared with the other conditions. Temporal 4-6 Hz power was lower in both the joint attention and social engagement conditions, compared with the nonsocial condition. Overall 6-9 Hz power was also lower in the joint attention condition, again indexing greater neural activation when compared to the nonsocial and language-only conditions.

There was no difference in 6-9 Hz power between the joint attention and social engagement conditions. Here we can see that 6-9 Hz power in the frontal region was lower in the joint attention condition compared with the language-only and nonsocial conditions. However, in the temporal region, 6-9 Hz power was lower in both the joint attention and social engagement conditions compared with the nonsocial condition.

With this paradigm, other EEG methods such as coherence across frequency coupling can be used to further examine the differential patterns of brain activity associated with social input. After watching this video, you should have a good understanding of how to comprehensibly assess infant EEG in both social and nonsocial contexts, as well as tease apart how different types of social inputs differentially relate to infant EEG.