2.2.1. Visual Orientation Attention Task

Similar to a previous study on DS and TD children [35], we tested infants in a visual orientation attention task. In this task we measured infants' looking latency to visual stimuli, here flashing lights. Infants were seated on their caregiver's lap in a testing booth facing the central green light, while two red lights were placed laterally from the infant. Infants' looking behavior was monitored on a camera (Logitech c920, Logitech, Fremont, CA, USA) and online coded by an experimenter placed outside the booth. Every trial began by flashing the central green light. Once the infant orients toward it, this light turns off and one of the lateral red lights starts to flash. When the infant directs its look toward the lateral red light, the experimenter records this by pushing a button on the keyboard. The lateral red light continues to flash for 2 s and then turns off, while the green-central

light starts flashing and a new trial begins. Infants' orientation latency is measured as the time between the onset of flashing of the lateral red light and the moment when infants look away from the central green light towards the lateral red light. If an infant did not direct its look to the central light, the experimenter played a short infant-friendly sound to recover infants' attention to the task. Moreover, if the experimenter noticed that the infant is not attending to the lateral light for a significantly long period (i.e., longer than 8 s), the trial ended by turning off the red light and initiating the green light. The 8-s reference was used as it was the maximum trial duration in [35]. There was a maximum of 10 trials (5 on the left and 5 on the right), and the presentation of the left vs. right lateral trials was randomized. The task stopped if an infant lost interest in the task, therefore the number of trials might vary across infants. Stimuli presentation was controlled by the Look software [38]. The time of infants' orientation latency from the central green light to the lateral red light was also recorded by the software.
