When a sparkler is twirled rapidly, people perceive a circle of light. This occurs because:. a. the trail you see is caused by sparks left behind from the sparkler. b. due to its differing wavelengths, the light from the sparkler continues to radiate for about a second after it goes out. c. the length of iconic memory (the persistence of vision) is about a fraction of a second. d. Gestalt principles work to complete the circle in our minds.