124 Perception is Ambiguous

Visual perception is often ambiguous. Our perception of a scene is an interpretation of the retinal images. The exact mechanisms that our visual brains use to represent and wrestle with uncertainty are open questions. Here are some visual experiences that illustrate the problem of ambiguity:

• Figure/ground segmentation. Low-level features (lines, edges, textures) provide clues about what belongs with what, but high-level interpretation (shape, scene layout) is also needed to separate foreground and background.
• Vase/Face: when equal evidence exists for multiple interpretations, we experience spontaneous switching between perceptual states. Perhaps this is because feedback has not amplified a “winning” response in V1. For example, refer to the figure above.
• Aperture problem. When we only see part of an image, we can perceive line segments as moving either horizontally or vertically.
• Shading and light.
  • Light from above: when a scene is ambiguous, our perception of shape relies on the assumption that light is coming from above and casting shadows downward.
  • Shape from shading: our perceptions of lighting, lightness, and shape are interrelated.