Final answer:
Astrid demonstrated the binocular disparity cue of depth perception, which decreases as the object moves farther away.
Step-by-step explanation:
Astrid has just demonstrated the binocular disparity cue of depth perception. When Astrid holds a pencil close to her nose and alternates opening and closing each eye, she experiences a visual effect where the pencil seems to shift position. This is due to the slightly different view each eye has of the pencil, known as binocular disparity, which is the basis for our binocular depth perception. As she moves the pencil farther away, these shifts become less noticeable because the disparity between the two images seen by each eye reduces. To summarize, when nearby, the binocular disparity is more prominent, but it lessens with distance, which tells the brain about the object's depth, aiding in forming a three-dimensional understanding of the space around us.