Illusory Contours

Have you ever experienced a situation where you can identify an object or shape without needing the contour (or outline) of it?
In visual illusion👁️‍🗨️, this is known as illusory contours, where you can perceive the outlines of an unexisting shape😲!

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What is Illusory Contour?

Illusory contours refer to visual illusions of perceiving and recognizing contours in an object that is not physically present (none exist).

Examples of Illusory Contours

1️⃣Kanizsa Triangle (Kanzsa, 1955)

The Kanizsa Triangle was first created by Italian psychologist Gaetano Kanizsa in 1955. As shown in the image above, a white upside-down triangle can be perceived as occluding the upright triangle and the three circles even though there are no explicit outlines whatsoever. Besides that, the white upside-down triangle also appears brighter than the surrounding white background. In fact, the white upside-down triangle actually does not exist at all and it has the same brightness as the background!

2️⃣Ehrenstein Illusion (Ehrenstein, 1941)

The Ehrenstein illusion was first described by a German psychologist named Walter Ehrenstein in 1941. It is one of the classic examples of illusory contours illusions. It is generated by a configuration of twelve-line segments which induce the perception of an illusory circle whereby the circle literally does not exist at all. The circle also appears to be brighter than the background even though it is actually having the exact same colour as the background.

Illusory Contours Explanations

Have you ever wondered why we can perceive and recognize a shape even though it does not have an outline😎? We will share three different perspectives to explain the illusory contours:

1️⃣Gestalt Principles - Law of Closure

According to the law of closure from Gestalt Principles, it suggests that when we perceive an image or an object, even though it is incomplete, we are more likely to perceive it as a whole. Therefore, when perceiving a stimulus we would automatically fill up the gaps and the missing information of the image or object to help us to form a recognizable object or shape and recognize it. In Kanizsa Triangle, we “self-complete” the contour lines to form an upside-down triangle by interpreting the three pac-mac as the corners of the triangles.

2️⃣Phantom edge phenomena

Next, the phantom edge phenomenon suggests that the reason why we perceive the unexisting outline is because our brain cells use the surrounding existing information to infer the nature of the missing part in the image or object, which allows us to complete the perception of a partially hidden object. Using the Kanizsa triangle as an example, our brain cells use the location and the mouth of the three pac-man to make an inference that the white upside-down triangle is placed in the middle.

3️⃣Top-down Processing

Last but not least, top-down processing is a form of processing that we use our learned knowledge and past experiences to help us in the process of perception and recognition. It helps us to understand the stimuli (figure) with the use of prior knowledge to make sense, process, and interpret the sensory information. For example, in the Kanizsa triangle, we used our prior knowledge to interpret that there is a “nonexistent” triangle that occludes the three circles equally and the upright triangle instead of interpreting it as 3 incomplete circles or incomplete upright triangles. As a result, this process helps us to explain the ambiguities of a stimulus in a plausible manner with the use of our existing knowledge.

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In essence, by understanding illusory contours we learned that there’s always both sides of every story, never assume what you see or hear is all of the truth, instead go find out the real truth. As quoted from Thomas Lloyd Qualls: “Things are often not what they seem. But, sometimes they are. The trick is to learn what is real.”

Hope you find this illusion interesting and thank you for taking the time to read this article😁!

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References/Resources:

1. Ehrenstein illusion - New World Encyclopedia
2. Ehrenstein illusion - Scholarpedia
3. Illusory Contours (hanover.edu)
4. Illusory Contours | Optical Illusions Wiki | Fandom
5. Kanizsa triangle - New World Encyclopedia
6. Kanizsa Triangle - The Illusions Index
7. The Kanizsa Triangle Illusion
8. The Kanizsa Triangle Illusion | What is Psychology?
9. Top-Down Processing | Simply Psychology
10. What Is Top-Down Processing? Definition and Examples (thoughtco.com)
11. 7 Gestalt Principles of Visual Perception: Cognitive Psychology for UX | UserTesting Blog