Fig 1.
This figure shows an overview of the study design and the methods used with respect to the age of the infant.
Please note that infants viewed photographic images of real faces (see Materials and methods) and that the facial images shown here were computer generated with the FaceGen software (https://facegen.com) for illustrative purposes. fNIRS, functional near-infrared spectroscopy.
Fig 2.
A: This illustrates the eye tracking paradigm employed in the current study at age 7 months. Note that the eye tracking experiment followed the fNIRS experiment. As shown here, infants were presented with experimental trials consisting of a side-by-side presentation of a neutral face and an emotional (happy, angry, or fearful) face. Note that in the actual experiment, the side on which an emotional face and neutral face were presented was counterbalanced, and the face identity changes were pseudorandomized (see Materials and methods for details). B: This illustrates the 2 areas of interest (face and eyes) that were used in the analysis of the eye tracking data. Please note that infants viewed photographic images of real faces (see Materials and methods) and that the facial images shown here were computer generated with the FaceGen software (https://facegen.com) for illustrative purposes. fNIRS, functional near-infrared spectroscopy.
Fig 3.
Attention to fearful faces, but not happy or angry faces, predicts altruistic behavior.
This shows partial regression plots from a multiple regression illustrating the specific impact of duration of first fixation on a fearful face when compared to the other facial expressions presented in the experiment (left) and looking bias to fearful faces when compared to the other facial expressions presented in the experiment (right) in predicting altruistic behavior measured as frequency of helping at 14 months (plotted on the y-axis; residuals). Please note that infants viewed photographic images of real faces (see Materials and methods) and that the facial images shown here were computer generated with the FaceGen software (https://facegen.com) for illustrative purposes. Underlying data are available through the Open Science Framework (https://osf.io/znjr7/). ns, not significant.
Table 1.
This is an overview of the eye tracking and fNIRS findings when altruistic behavior is measured as a continuous variable (frequency of helping, ranging from 0 to 6).
Note that a positive ß value reflects that this variable is positively associated with altruistic behavior. Underlying data are available through the Open Science Framework, https://osf.io/znjr7/.
Table 2.
This is an overview of the eye tracking and fNIRS findings when altruistic behavior is measured as a binary variable (help versus no help).
Note that a positive b value reflects that this variable is positively associated with altruistic behavior. Underlying data are available through the Open Science Framework, https://osf.io/znjr7/.
Fig 4.
This combined violin–box plot shows that the duration of the first fixation on fearful faces at 7 months of age was significantly longer in infants who helped at age 14 months compared to infants who did not help (using altruistic behavior as a binary measure).
Note that the duration of the first fixation on fearful faces at 7 months significantly predicts altruistic behavior at 14 months in a logistical regression (see Results and Table 2). *** p < 0.001. Underlying data are available through the Open Science Framework, https://osf.io/znjr7/.
Fig 5.
A: This illustrates the fNIRS paradigm employed in the current study at age 7 months. Note that the fNIRS experiment preceded the eye tracking experiment. Infants viewed at least 6 seconds of nonsocial (inanimate) baseline stimuli followed by 6 seconds of emotional (happy, angry, and fearful) test stimuli. Dynamically changing stimuli were administered by presenting neutral faces that rapidly and repeatedly changed to one of the 3 emotions. B: This shows the fNIRS channel layout (right) with the nose plotted up and the 3 ROIs marked by different colors (dlPFC = blue; IFC = violet; STC = green; TPJ = red) on the left with reference to the 10–20 system commonly used in EEG research. On the left, these ROIs are also shown when projected onto the cortical surface of a frontal-view (bottom) and lateral-view brain (top). Please note that infants viewed photographic images of real faces (see Materials and methods) and that the facial images shown here were computer generated with the FaceGen software (https://facegen.com) for illustrative purposes. EEG, electro-encephalography; fNIRS, functional near-infrared spectroscopy; IFC, inferior frontal cortex; ROI, region of interest; STC, superior temporal cortex; TPJ, temporo-parietal junction.