Have you ever looked at a landscape and wondered if you’re seeing a plateau rising above the ground or a series of valleys cut into it? This kind of visual confusion is similar to the famous duck/rabbit illusion, where our perception can flip between two interpretations. These are examples of multistable perceptual illusions, which often occur when we view shaded relief maps or aerial and satellite photos of terrain.
The way we perceive these illusions boils down to two main reasons: our experience with sunlight on Earth and the symmetry of light and shadows. On Earth, we’re accustomed to light coming from above because the sun is usually overhead. This means shadows typically fall below objects. This understanding is so ingrained in us that it influences everything from religious metaphors to art and design conventions.
Our brains use the position of shadows to interpret the 3D shape of objects. If a shadow is at the bottom of a feature, we perceive it as convex, or bulging out. Conversely, if the shadow is at the top, we see it as concave, or dented in. However, there’s a tricky symmetry in nature: a concave feature lit from one side can cast similar shadows to a convex feature lit from the opposite side. This can lead to misinterpretations, such as seeing a dent lit from below as a bump, or vice versa.
When viewing landscapes from above, our perception of whether a feature is a mountain or a valley largely depends on the direction of the light source. We tend to see geographic features as mountains when shadows are at the bottom and as valleys when shadows are at the top. This perception is accurate only if the light is coming from the top of the image.
Interestingly, cartographers often depict light coming from the north in shaded relief maps of the northern hemisphere, even though the sun never shines from that direction in most places. This artistic choice helps ensure that the geographic features are communicated accurately, even if it means sacrificing the true position of the sun.
If you ever find yourself confused by a map or an aerial photo, try rotating it 180 degrees. This simple trick can help your brain switch its perception, making the map easier to understand. This insight came to me after I mistakenly perceived valleys as mountains while looking at a map upside down!
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Engage with an online platform that allows you to manipulate shaded relief maps. Rotate the maps 180 degrees and observe how your perception of the landscape changes. Reflect on how light direction influences your interpretation of geographic features.
Conduct a simple experiment using a lamp and various objects to create shadows. Position the light source from different angles and document how the shadows alter your perception of the objects’ shapes. Discuss your findings with peers to understand the role of light direction in perception.
Analyze the famous duck/rabbit illusion and other similar images. Discuss in groups how these illusions demonstrate multistable perception. Consider how experience and context influence which interpretation your brain chooses first.
Participate in a workshop where you create your own shaded relief maps. Experiment with different light source directions and observe how it affects the readability and interpretation of the map. Share your maps with classmates and discuss the impact of artistic choices in cartography.
Join a seminar discussing the influence of light and shadow in art and design. Explore how artists use these elements to create depth and convey meaning. Reflect on how these principles relate to multistable perceptual illusions and share your insights with the group.
Landscape – The visible features of an area of land, often considered in terms of their aesthetic appeal or ecological significance – The landscape of the region is characterized by rolling hills and dense forests, offering a diverse range of habitats for wildlife.
Perception – The process of recognizing and interpreting sensory stimuli, particularly in understanding spatial relationships in geography – The perception of distance can be influenced by the presence of landmarks and the clarity of the atmosphere.
Shadows – Dark areas or shapes produced by a body coming between rays of light and a surface – In geography, shadows cast by mountains can affect local climate by reducing sunlight and lowering temperatures in the shaded areas.
Light – Electromagnetic radiation that is visible to the human eye and is responsible for the sense of sight – The angle of light during different times of the day can dramatically alter the appearance of a landscape.
Terrain – The physical features of a tract of land, including its elevation, slope, and orientation – The rugged terrain of the region makes it a challenging area for construction and transportation.
Geographic – Relating to the natural features, population, industries, etc., of a region – Geographic information systems (GIS) are used to analyze spatial data and make informed decisions about land use and resource management.
Features – Distinctive attributes or aspects of a landscape or region – The geographic features of the area include a series of interconnected lakes and a prominent mountain range.
Mountains – Large natural elevations of the earth’s surface rising abruptly from the surrounding level – The Andes Mountains are one of the longest mountain ranges in the world, stretching across seven South American countries.
Valleys – Low areas of land between hills or mountains, typically with a river or stream flowing through them – The fertile valleys of the region are ideal for agriculture, supporting a variety of crops and livestock.
Cartographers – Individuals who practice the art and science of making maps – Cartographers use advanced technology and data analysis to create accurate and detailed maps for navigation and research.
