2.2.2. Audiovisual Task

Infants' eye-gaze was recorded while watching 4-s-long videos of an animated character (Noddy) talking and waving at the infant (Figure 1). Videos were part of a stress perception task where they were inserted after each block as a reinforcer [39]. Auditorily, four different reinforcing passages were paired with the same video (e.g., "That's it! We are going to play one more time" (Four following passages were used: "É isso! Vamos jogar mais uma vez" (That's it! We are going to play one more time); "Muito bem. Vamos continuar o nosso jogo" (Well done! We are going to continue our game); "Muito bem! Este jogo é muito divertido" (Well done! This game is a lot of fun); "Parabéns! Vejo que estás mesmo a gostar disto" (Good! You are really enjoying the game)). The video did not change visually throughout the task, only the auditory passages. The order of presentation of the video with the different passages was randomized between infants. Intentionally, the Noddy character was presented centrally in the video, against a colorful and attractive background, to assess infants' attention to visual linguistic and paralinguistic communicative cues (the face, the arm) versus non-linguistic objects (the background). In total, infants could be presented with up to eight videos. However, the stress perception task stopped when infants lost interest in the task, therefore infants varied in how many videos they were presented with. *Brain Sci.* **2021**, *11*, x FOR PEER REVIEW 5 of 12

**Figure 1.** Still-example frame from the audiovisual task. Marked in colors are the areas of interest analyzed in the task: the face, the eyes, the mouth, the arm, and the background. **Figure 1.** Still-example frame from the audiovisual task. Marked in colors are the areas of interest analyzed in the task: the face, the eyes, the mouth, the arm, and the background.

pleted all 10 trials. In the DS group, 6 out of 7 infants completed 10 trials (M = 9.28, range from 5–10). In the TD sample, 16 out of 24 infants provided data for all trials (M = 8.95; range from 5–10 trials). Infants' orientation latency for the two groups is provided in Figure 2. Because sample size differed across groups, we performed a linear-mixed model analysis with infants' orientation latency as the dependent variable, group (DS and TD) as a fixed effect, while by-subject intercept was set as a random effect. Using the lmerTest [40] package in R, we observed that the DS group revealed significantly longer latency than the TD group (intercept = 6.29, DS estimate = 2.46, SE = 0.86, t = 2.85, *p* = 0.008, 95% CI: 0.77–4.16). Additionally, we compared the number of trials longer than 8 s across groups. A Wilcoxon-Mann-Whitney test revealed that DS infants exhibited more trials longer than 8 s (M = 3.0, SD = 2.0) than TD infants (M = 1.29, SD = 1.5; Z = 2.19, *p* =

Infants' looking times to the screen were recorded with an eye-tracker. We defined dynamic areas of interest (AOI) covering the background, the arm, the face, the eyes, and the mouth (Figure 1). For each trial, we calculated the proportion of looking time to the AOIs in comparison to the whole screen. Next, for each infant we averaged proportions across all trials. The total number of trials differed across infants, depending on how long they were interested in the task (between 1 and 8 blocks). A Wilcoxon-Mann-Whitney test revealed that groups did not differ in the number of completed trials (MTD = 3.91, range 2– 6; MDS = 3.4, range 2–5; Z = −0.71, *p* = 0.47, r = 0.13). The looking patterns for the two

**3. Results** 

0.028, r = 0.39).

*3.2. Audiovisual Task* 

groups of infants are depicted in Figure 3.

*3.1. Visual Orientation Task* 

Infants were seated in the caregiver's lap in a dimmed testing booth, facing the stimuli presentation monitor (Dell LCD screen in 1680 × 1050 pixel resolution) on ~70 cm distance from the monitor. Auditory stimuli were played over speakers (Genious) placed behind the monitor. Infants' eye-gaze was recorded using the SMI RED500 eye-tracker, whereas the SMI Experimenter Center and iView X software-controlled stimuli presentation.
