Final answer:
Inattentional blindness is the visual system aspect responsible for the magician's trick, where focus on a specific task prevents the observer from noticing other visible objects.
Step-by-step explanation:
The aspect of our visual system that allowed the magician to accomplish the illusion of making a ball disappear is known as inattentional blindness. This phenomenon occurs when an individual fails to notice a fully visible object because their attention is focused on another task or object. The studies conducted by Simons and Chabris are prime examples of inattentional blindness, where individuals did not notice obvious elements like a person in a gorilla costume or a red cross due to their concentrated focus on a different visual task. This suggests that our perception is not a perfect representation of the environment, but rather a construction of focused attention combined with brain processing that actively interprets and projects what we see to make sense of the world around us.