During a parade, a marching band is arranged on a field in a grid formation, with equal spacing between every member. The members in the first row all wear red uniforms, the members in the second row all wear blue uniforms, the third row wears red, and so on. Why would an observer be more likely to perceive the band as a series of horizontal rows rather than a series of vertical columns?

Imagine an image composed of three black circles, each with a wedge-shaped section removed, arranged to look like 'Pac-Man' figures. The 'mouths' of these figures all face inward, creating the perception of a solid white triangle in the center, even though no lines are drawn to form this triangle. Which of the following statements best explains why most people see this central triangle?