Table 10 Additional information on eye-tracking and fNIRS measures
Measure | Description |
|---|---|
Eye-tracking | Participants sat approximately 65-cm distance to the screen. Sampling frequency was 300 Hz for part of the sample (37–42%) and 60 Hz for another part of the sample (58–63%). A webcam recorded the child’s behavior during the test assessment |
- VOF task | Each stimulus is presented in one of four quadrants on the screen, while the other quadrants remain empty. According to the principle of preferential looking, if a child sees the stimulus, it will look at it |
- Social preference task | Participants were presented a ring of five stimuli, containing an image of a face with direct gaze, a scrambled inverted face (noise face), and three non-social stimuli (car, phone, and bird). The current experiment used six slides for a duration of 10 s each. A fixation stimulus (cartoon) was presented in the center of the screen for three seconds in between slides |
fNIRS | The Artinis Brite 23 was originally developed for use on the frontal regions, but was used in this study on the Superior Temporal Sulcus (STS) region with custom made headcaps utilizing 18 channels. We obtained good signal using this setup in healthy subjects. The system used two wavelengths of emitting light at 760 and 850 nm. Source-detector separation was 25 mm for cap sizes 46 to 50 cm and 30 mm for cap sizes 52 to 58 cm. Participants were given the option to watch an entertaining video, while the headcap was placed on the head. The task entailed a visual-social condition, non-vocal condition, and vocal condition, displayed in a repeating loop six times (total task duration approximately 6 min). In between the different conditions was a baseline period, which consisted of visual non-social stimuli (pictures of vehicles). The visual social dynamic stimuli involved videos of a person who either moved her eyes left or right or performed hand games (“peek-a-boo” and “incy wincy spider”). The non-vocal condition consisted of environmental sounds (running water, squeaky toys), while the vocal condition contained non-language vocalizations, such as laughing and yawning |