What causes Brenda to perceive a white duck in the shade as lighter than a blackbird in sunlight?

Brightness constancy describes the phenomenon where the perceived brightness of an object remains relatively constant even when the lighting conditions change. In this scenario, Brenda perceives a white duck in the shade as lighter than a blackbird in sunlight due to the context in which she observes these objects. The brain compensates for the different light conditions, maintaining a perception of the duck's brightness relative to its environment.

Because the duck is in the shade, Brenda's visual system adjusts for the dimmer light by enhancing her perception of its brightness, ensuring that she still recognizes it as a white object rather than one that appears lighter due to reduced light. Meanwhile, the blackbird, which is in direct sunlight, may appear to her as darker against its bright surroundings. This relative perception leads to the conclusion that brightness constancy is at play, allowing for consistent identification of colors and brightness despite varying environmental lighting.