80% Witness Its Growth: Unveiling the Secrets Behind the “Black Circle” Optical Illusion in Science and Technology

September 18, 2025

A seemingly simple optical illusion – a white background featuring black dots and a central dark spot – is prompting a significant reassessment of how the human visual system operates. Many observers report a sensation of the dark spot growing, creating the feeling of falling into a tunnel, though this effect isn’t experienced by everyone. Now, groundbreaking research indicates the illusion’s origin may not be within the brain, as previously thought, but rather in the eye itself.

The Expanding Hole Illusion: A Deep Dive

First observed in 2022 by teams at the University of Oslo in Norway and Ritsumeikan University in Japan, the “expanding hole” illusion triggers automatic visual reflexes, even deceiving them. Approximately 86 percent of individuals exposed to the image perceive it as enlarging, accompanied by involuntary pupil dilation-a reaction mimicking the response to increasing darkness, despite the absence of actual light change. This initial discovery highlighted that our pupils react not just to light, but also to perceived light.

“We demonstrated that the pupil reacts to how we perceive light, even when that ‘light’ is illusory,” explained Psychologist Bruno Laeng, the principal author of the original study published in Frontiers in Human Neuroscience.

The expanding hole illusion (left) and its inverted counterpart, causing pupil constriction. Source: Nematzadeh et al., Arxiv (2025)

Retinal Processing: A Paradigm Shift

prior theories positioned the brain as the source of the illusion, interpreting the black hole as a pathway to a three-dimensional tunnel. However, recent work spearheaded by Nasim Nematzadeh at Flinders University in Australia, challenges this, focusing instead on the role of the retina.Nematzadeh’s team modeled the behavior of ganglion cells-nerve cells responsible for processing contrasts and adapting to varying light levels.

Their model revealed that ganglion cells don’t merely transmit data to the brain; they also communicate with neighboring cells. This interaction, according to the research, creates a cascading effect of perceived darkness, extending beyond the central hole and producing the illusion of expansion. “neighborhood cells are somehow contributing to the perception of what we see,” Nematzadeh stated. “It’s changing all the time.”

Essentially, when the ganglion cells identify the dark center, they trigger neighboring cells to register more shadow than is actually present, causing the black area to seemingly grow.This finding is detailed in a preliminary study published on ArXiv.

Jolyon Troscianko, a neuroscientist at the University of Exeter, believes this retinal description is a significant advancement, offering a more concrete and testable framework than previous cognitive-based theories. “If you think of an explanation that depends on the quite early visual processing in your brain, then that is – for me – more useful,” he noted.

Implications Beyond the Illusion

The implications of this discovery stretch beyond understanding a curious optical phenomenon. Researchers suggest the same principles could explain other visual patterns in nature. As an example, understanding how the retina processes contrasting elements might offer new insights into the function of zebra stripes, butterfly wing patterns, and camouflage. A recent article in Current Biology highlighted similar retinal processing in animal camouflage patterns (https://www.cell.com/current-biology/fulltext/S0960-9822(23)01543-4).

Moreover, Laeng previously suggested that pupillary reflexes triggered by illusions could be valuable in studying other cognitive functions, such as visual inventiveness. Studies have tied pupil changes to conditions like aphantasia-the inability to form mental images.

Aspect	Previous Understanding	New Findings
Origin of Illusion	Brain’s interpretation of 3D space	retinal processing by ganglion cells
Key Mechanism	Higher-level cognitive processes	Interaction between neighboring ganglion cells
pupil dilation	Response to perceived light from the brain	Response to retinal processing of contrast

Interestingly, individual experiences of the illusion vary. The Norwegian study revealed that 14 percent of participants didn’t perceive any expansion with the black hole, while 20 percent didn’t experience it with colored versions. The strength of the physiological response – pupil diameter change – also differed based on individual perception.

These illusions aren’t merely visual quirks; they offer a window into the complexities of our visual system, which functions not as a passive recorder of light, but as a dynamic and predictive system influencing perception, attention, and imagination.

Understanding Visual Illusions: A lasting Perspective

Visual illusions are powerful tools for neuroscientists, offering invaluable insights into the mechanisms of perception. They demonstrate that what we “see” isn’t always an accurate representation of reality, but rather a construction of our brains and eyes.Ongoing research continues to unravel the intricate interplay between sensory input and cognitive processing, expanding our understanding of consciousness itself.

Did You Know? The study of visual illusions dates back centuries, with early explorations by philosophers and artists seeking to understand the nature of perception.

Pro Tip: Experiment with the illusion yourself! Focus on the central dark spot for 30-60 seconds and observe any changes in your perception. Note if you experience the sensation of expansion and whether your vision feels altered.

Frequently Asked Questions about the Expanding Hole Illusion

• What is the expanding hole illusion? It’s an optical illusion where a dark spot appears to grow larger as you stare at it, creating a sensation of falling into a tunnel.
• What causes the illusion of an expanding hole? Recent research suggests the illusion originates in the retina, due to interactions between ganglion cells.
• Does everyone experience the expanding hole illusion? No, approximately 14-20% of individuals do not perceive the illusion, and the intensity of the effect varies.
• How does the retina contribute to this illusion? Ganglion cells signal neighboring cells, creating a perceived expansion of the dark area beyond its actual size.
• What are the potential implications of this research? It could provide insight into visual processing, camouflage, and cognitive functions like visual imagination.
• Is this illusion perilous? No, the illusion is harmless but can cause a momentary disconcerting sensation.
• Could this illusion help us understand other visual phenomena in nature? Yes, it provides a new framework for understanding patterns like zebra stripes and camouflage.

What are your thoughts on this mind-bending illusion? Have you experienced it yourself, and if so, how did it feel? Share your experiences in the comments below!

How might understanding the neural mechanisms behind the expanding circle illusion inform the design of more immersive and cozy VR/AR experiences?

The Expanding Black Circle: A Perceptual Phenomenon

the “Black Circle” illusion, also known as the expanding circle illusion or simply the peripheral drift illusion, is a captivating visual phenomenon where a static black circle appears to grow in size when fixated upon. Roughly 80% of observers report experiencing this effect, making it a remarkably consistent perceptual experience. This isn’t a trick of the eye, but a fascinating interplay between neural processing, eye movements, and the way our brains interpret visual data. Understanding this illusion requires delving into the complexities of human vision and its limitations.

how Does the Illusion Work? The Neuroscience Behind It

The core of the illusion lies in the way our visual system processes contrast and motion. Several theories attempt to explain the expanding circle effect:

* Neural fatigue: One prominent theory suggests that prolonged exposure to the high-contrast black circle causes fatigue in neurons responsible for detecting that specific stimulus. This fatigue leads to a diminished response, making the circle seem larger as the brain attempts to compensate.

* Microsaccades: Our eyes aren’t perfectly still; they constantly make tiny, involuntary movements called microsaccades. These movements are crucial for maintaining visual clarity. When fixating on the black circle, microsaccades may subtly shift the image across the retina. the brain interprets these shifts as outward expansion, especially in the periphery.

* Lateral Inhibition: This neurological process enhances edges and contrasts. The black circle’s sharp edge activates surrounding neurons, which then inhibit the activity of neurons directly adjacent to it. This inhibition can create a perception of enlargement.

* Motion Perception Pathways: The brain has dedicated pathways for processing motion. Even though the circle isn’t moving, the neural activity generated by the contrast and microsaccades can activate these pathways, leading to the illusion of expansion.

The Role of Contrast and Surroundings

The strength of the illusion is heavily influenced by several factors:

* Contrast: Higher contrast between the black circle and its background intensifies the effect.A stark black circle on a white background produces a more pronounced illusion than a dark gray circle on a light gray background.

* Background Complexity: A simple, uniform background generally enhances the illusion. Cluttered backgrounds can distract the visual system and reduce its sensitivity to the expanding circle.

* Circle Size: The size of the circle itself plays a role. Moderate-sized circles tend to elicit the strongest response.

* Viewing Distance: The distance from which the illusion is viewed can also affect its intensity.

Applications in Science and Technology: Beyond a Visual Curiosity

The study of the expanding circle illusion isn’t merely an academic exercise. It has implications for several fields:

* Visual Neuroscience Research: The illusion serves as a valuable tool for researchers studying the mechanisms of visual perception, motion detection, and neural adaptation. It allows scientists to probe the inner workings of the brain in a controlled manner.

* Human-Computer Interaction (HCI): Understanding how the brain perceives visual stimuli is crucial for designing effective user interfaces. The illusion highlights the importance of contrast,background clutter,and dynamic elements in capturing and maintaining user attention.

* Virtual Reality (VR) and Augmented Reality (AR): Developers creating immersive VR/AR experiences need to be aware of perceptual illusions like the expanding circle. Incorrectly rendered visuals could trigger unintended illusions, leading to discomfort or disorientation.

* Medical Diagnostics: Research suggests that sensitivity to visual illusions can be affected by neurological conditions. Changes in perception of illusions like this one may serve as an early indicator of certain disorders.

* Advertising and Marketing: While ethically questionable to exploit, the principles behind the illusion can inform visual design choices in advertising to attract attention and influence perception.

Real-world Examples & Case Studies

While not a direct request, the principles behind the expanding circle illusion are utilized in various visual effects in film and gaming. Such as, subtle animations and contrast adjustments can create a sense of depth or movement, even when the image is static.

A 2018 study published in Journal of Vision used the illusion to investigate the role of predictive coding in visual perception. Researchers found that the illusion’s strength was correlated with the brain’s ability to predict visual input,suggesting that the brain actively constructs our visual reality based on prior expectations.

Benefits of Studying Visual Illusions

Delving into the world of visual illusions offers several benefits:

* Enhanced Understanding of Perception: It provides insights into the complex processes that shape our subjective experience of reality.

* Improved Critical Thinking: It encourages us to question our assumptions about how we see the world.

* Creative Inspiration: It can spark new ideas in art, design, and technology.

* Potential for Technological Advancement: The knowledge gained from studying illusions can lead to innovations in fields like VR/AR and HCI.

Practical Tips for Experiencing the Illusion

Want to experience the expanding circle illusion firsthand? Here’s how:

1. Find a Dark Circle: Locate a simple image of a black circle on a white background.
2. Fixate Your Gaze: Stare directly at the center of the circle for 20-30 seconds.
3. Observe the Periphery: Pay attention to the area surrounding the circle. You should begin to notice the