Human Vision Explained

Like all primates, humans are highly reliant on visual cues for survival. Our eyes are designed to detect a specific range of electromagnetic radiation, specifically between 380 and 700 nanometers, known as the visible light spectrum.

Light enters our eyes through a transparent, dome-shaped structure called the cornea, which helps focus it. The iris, the colored part of the eye, regulates the amount of light that enters by adjusting the size of the pupil.

Once light passes through the pupil, it goes through the lens, which, along with the cornea, focuses the light on the retina, a light-sensitive layer. The retina contains photoreceptors that convert light into electrical signals sent to the brain, where they're interpreted as images.

There are two main types of photoreceptors: rods and cones. Humans have over 100 million rod cells for seeing in low light, but these do not perceive color, leading to a grayscale view at night. Conversely, cones require more light and enable color vision, with most people possessing around 6 million cones divided into three types: red, blue, and green. This combination allows us to perceive millions of colors.

Interestingly, some individuals possess an extra cone type, a condition known as tetrachromacy, which lets them see even more colors. Research indicates that this trait is notably more prevalent among women, with studies suggesting that about 12% may have it.

Conversely, men are more prone to color blindness, with studies showing that around 8% of Caucasian males have color vision deficiencies, compared to just 0.5% of females from all ethnic backgrounds.

While human vision is remarkable, it represents just one of many evolutionary adaptations across the animal kingdom. Thanks to innovative research and technology, we are uncovering the unique ways animals perceive their environments.

Beyond Human Vision

While we may never fully grasp the subjective experiences of other animals, science can provide insights into their perspectives. By examining the anatomy of an animal's eyes, researchers can infer their color perception capabilities.

For instance, species that thrive in low-light conditions, such as cats, possess significantly more rod cells—often six to eight times more than humans—enabling them to see better in darkness. Conversely, humans have more cone cells, allowing us to see effectively in brighter environments.

Many animals can perceive wavelengths beyond the visible spectrum, including ultraviolet (UV) light, which is invisible to humans. This ability is present in creatures like reptiles, honeybees, certain fish, and most birds.

Recent technological advancements have enabled scientists to visualize how these animals see. Two primary methods are used: capturing images with specialized cameras that detect a broader light spectrum and employing spectrophotometry to analyze light absorption at varying wavelengths.

While these techniques are groundbreaking, they have limitations. Both methods are time-intensive and best suited for controlled conditions, and they often yield only static images, limiting our understanding of how animals perceive movement.

Biologists studying animal behavior are particularly interested in how animals perceive motion. Vera Vasas, a biologist at the University of Sussex and the lead author of an exciting new study, highlighted the importance of color changes in signaling.

New Research Breakthrough

In January 2024, Vasas and her international team published their findings in PLOS Biology, introducing a novel camera system and software designed to capture how various species see the world in motion.

Using a 3-D printer, the team created a portable enclosure with a beam splitter to differentiate between UV and human-visible light. They recorded light streams using two cameras: one capturing the human spectrum and the other focused on UV light. By overlapping these videos, they produced a single clip showcasing a broader light spectrum and the visual perspectives of different species.

Their innovative method represents a significant advancement, providing scientists and filmmakers with a new, empirically backed approach to depicting the perceptual worlds of nonhuman animals.

Applications and Implications

Beyond satisfying curiosity about how other animals perceive their surroundings, this research has the potential to revolutionize animal studies.

Jolyon Troscianko, a visual ecologist at the University of Exeter, noted that this new video technique addresses critical gaps in our understanding of animal vision. He emphasized that the movement of various signals in nature holds valuable information about animal behaviors, including mating and defense displays.

This technology can also enhance conservation efforts by minimizing human interference with wildlife. Understanding how animals perceive their environments can inform strategies like designing bird-safe windows or mitigating the effects of light pollution.

Impressive Accuracy

The transition from static images to dynamic videos of animal vision is a remarkable achievement. Vasas described the accuracy of their technique as "shockingly accurate," revealing previously unseen phenomena in the natural world. For instance, they observed color shifts in iridescent peacock feathers that are invisible to humans but perceptible to other peafowl.

The research team's findings offer a glimpse into aspects of the natural world that remain unexplored, and Vasas anticipates many future discoveries as the technology develops.

Cost-Effective and High-Quality

One common challenge in scientific advancements is cost. While supercomputers represent significant technological progress, they are often prohibitively expensive and energy-intensive. In contrast, Vasas and her team's system is not only more affordable but also delivers better image quality than existing methods.

According to Daniel Hanley, a senior author on the study, the use of 3-D printed materials and readily available commercial components allows for a system that costs just a few thousand dollars—far less than current techniques.

An Ongoing Journey

Although the new camera and software are groundbreaking and cost-effective, they do come with limitations. The current system has a restricted frame rate and requires manual focus, making it challenging to track fast-moving animals. Additionally, it struggles in low-light conditions.

Most importantly, while offering high-quality images, the system cannot capture all aspects of animal vision. Many species see in infrared or polarized light spectrums, necessitating further development.

Nevertheless, this research opens a unique window into animal perspectives, paving the way for more exploration in the future.

Shifting Perspectives

As a child, I once asked my father if he saw the same green grass that I did. He replied that we could never truly know, as we cannot experience another person's perception. This conversation profoundly impacted my worldview, sparking a lifelong curiosity about how others think and perceive their surroundings.

While my father and I may share the same species and similar visual functions, other animals possess distinct anatomies and senses, leading to diverse perspectives. Today, science is beginning to achieve what once seemed impossible—gaining insights into how animals view their world.

This article was originally published in the author’s free newsletter, Curious Adventure. It was edited and republished on Medium with her consent.

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