Seeing the Unseen: Unraveling the Mysteries of Color Perception

(Posted on Saturday, December 23, 2023)

This story is part of a series on the current progression in Regenerative Medicine. This piece is part of a series dedicated to the eye and improvements in restoring vision. 

In 1999, I defined regenerative medicine as the collection of interventions that restore tissues and organs damaged by disease, injured by trauma, or worn by time to normal function. I include a full spectrum of chemical, gene, and protein-based medicines, cell-based therapies, and biomechanical interventions that achieve that goal.

Imagine standing atop a mountain, gazing out at a breathtaking sunset. The sky is ablaze with a riot of colors – reds, oranges, yellows, and purples – all merging and blending to create a stunning display of natural beauty. From the deepest blues of the ocean to the lush greens of the forests, colors are an essential part of our world, adding depth and dimension to everything around us. Yet, the intricacies of color perception are often overlooked.

Each color we see results from a complex interplay of light and our brain’s interpretation. The colors we perceive are not static but constantly shifting, changing with the light source and our biases. Cultural, biological, and individual factors influence how we perceive color, making color perception a multidimensional phenomenon.

In this essay, we explore the intricacies of color perception, including color blindness and the impact of color on mood and psychology.

Process of Color Perception

Color perception is a complex process involving light interaction with specialized photoreceptor cells in the retina. The visible light spectrum contains all the colors from violet to red. When light shines on an object, the physical properties of that object determine how it absorbs, reflects, and emits light, affecting how we visually perceive the object.

The perception of color involves the interaction of light with specialized photoreceptor cells in the retina called cones. Most mammalian retinae only contain two types of cones, sensitive to short and medium-wavelength light. Humans, however, have an additional cone sensitive to long-wavelength light at the red end of the visual spectrum. This additional cone allows us to see a broader range of colors than most mammals.

The first step in the visual cycle is the retinal’s light-mediated conformational change, which activates an associated opsin that acts as a protein-coupled receptor. Each cone type is associated with a different opsin with other genetic bases. These cones are responsible for color perception, and the specific wavelengths of light they absorb determine the perceived color.

Factors That Impact Perception of Color

Multiple factors can influence our perception of colors; sensory inputs are vital contributors to our perception of colors. One such input is what we see and the context in which we see it. The color’s surroundings can significantly impact our perception of it. 

For example, the perceived brightness of a color can be influenced by the background on which it is placed. Researchers have found that a red square set on a white background may appear brighter than the same red square placed on a black background. This effect, known as simultaneous contrast, occurs because the color receptors in our retinas are stimulated differently based on the surrounding colors. 

The context in which a color appears can also alter how we perceive its hue. The shade of blue may appear greener when surrounded by yellows than pinks. Thus, our perception of colors is determined by the colors themselves and the context in which they are presented, highlighting the complex and multifaceted nature of color perception.

Furthermore, research published in Frontiers in Psychology has shown that smells can impact our perception of colors. In some cases, specific odors can be strongly associated with particular colors, and the presence of these odors can subtly alter our color perception. For example, the smell of lemons may cause us to perceive yellow as brighter or more intense. Similarly, the scent of lavender may make us perceive shades of purple as more calming or soothing. This phenomenon can be seen in the visual below. 

The figure showcases the angle data for each odor relative to the control, revealing a general shift toward warm colors in the presence of any odor. While four odors (lemon, caramel, cherry, and coffee) align with their anticipated crossmodal correspondences, the expected green-blue color trend for peppermint was not observed. Error bars (dashed lines) denote the standard mean error. These findings were statistically validated, indicating a significant impact of odor on color perception and suggesting a potential crossmodal integration mechanism. 

Color Blindness and Brain Plasticity

Color blindness is when individuals have difficulty distinguishing between specific colors, usually red and green. This condition occurs when there is a defect in the M or L cone opsins on the X chromosome. In addition, S cone opsin defects can also occur, although less frequently. While color blindness cannot be cured, improving color discrimination is possible.

Our brains can change and adapt based on our experiences, known as brain plasticity. This phenomenon can potentially improve our color perception, especially in cases of color blindness. According to recent studies, experience actively influences circuits for color vision, which can alter color perception and persist even after the incident has ended.

In the study, researchers focused on color-deficient adults with inherited photopigment defects. Despite the defects, these individuals still experienced vivid color sensations. This indicates that their brains adapted to the neural circuitry associated with color vision. 

The researchers found that these color-deficient adults had altered weightings of inputs to chromatic channels, which points to a significant neural adjustment due to their inherited photopigment defect. This finding shows that chromatic experience can change color perception, and this change persists even after the experience has been discontinued.

This study provides compelling evidence that experience plays an active role in shaping the neural circuits associated with color perception. The ability of the visual system to adapt and change in response to experience offers great promise for the treatment of genetic disorders and the recovery from neurological damage. 

Understanding the mechanisms that underlie experience-dependent neural plasticity in the visual system will be critical for developing new therapies for visible diseases and improving the quality of life for millions of people.