Seeing a New Color

03 May, 2025

Every day, we are bombarded with countless sensory stimuli. Our sensory organs use information from their physical surroundings to perceive everything we see, eat, smell, hear, and feel. The neuroscience field has advanced our understanding of how we sense our environment. With advances in technology, is it possible to manipulate our senses? Could we trick our neurons into perceiving things that are not really in the environment?

Scientists’ first attempts at controlling perception were very crude. Dr. Wilder Penfield was working with epilepsy patients in the 1930s and 1940s. During the operations, he would explore the effects of delivering electric current directly to the exposed brain. When a specific point on the side of the brain was stimulated, one patient said, “three or four things danced before my memory,” and when the electrode was moved slightly, the patient heard music ¹. These were the first pieces of evidence that sensory information resides in our brains. They helped inform us about what brain regions are involved in specific functions such as sight, hearing, and motion, but they were not great at recreating these stimuli precisely. Many decades later, great improvements in neuroscience technology have provided greater precision, allowing researchers to deliver much more specific stimuli.

Researchers at the University of California – Berkeley have shown research subjects a new color. That is, neurotechnology has created a color beyond the normal human perception. To understand how it works, we need to understand how color vision works in the brain.

Simply put, colors are light waves of specific wavelengths. Millions of years of evolution have given primate neurons the ability to sense a subset of these wavelengths. We have three types of cone receptors in our retinas: those detecting (1) short, (2) middle, and (3) long wavelengths of light. Each can change information from photons to an electrical signal carried between neurons. One key concept is that each cone cell can detect a range of wavelengths, so there is overlap between the cones’ sensitivity ranges. Because of this “spectral overlap”, it is impossible for only one type of cone cell in our retinas to be activated.

The researchers developed a platform called “Oz” that aims to manually activate specific sets of cone cells. This goal requires two steps: First, the researchers must know the location of the specific types of cone cells, which varies between people. Cone distributions are irregular, so each individual’s cone map must be created separately. Once a map of the retina is created, the researchers must use lasers in specific patterns to activate the specific cone cells they want.

Using these principles, the researchers’ goal was to have participants see a new color, previously unavailable to their limited perception. They mapped the location of every middle wavelength receptor on their participants’ retinas and delivered a laser stimulus to only activate them. They used laser technology that only delivered light to this subset of cells, avoiding the usual overlap when a single wavelength of light activates multiple types of cone cells. ²

The result was Olo. Olo has been described as an extremely saturated teal or blue-green, but unlike any color they had seen before. It is named after the color space coordinates (0,1,0), representing only medium-wavelength cone activation without stimulating the short or long cone cells types.

_{This is the closest visible color to Olo}

Other stimuli were also possible with this system. The researchers delivered laser bursts corresponding to bars of specific orientations. Direct activation of cone cells corresponding to the image of a bar was sufficient for the participants to reliably determine its orientation. Similarly, when laser microdoses changed over time to correspond to a rotating dot, participants were able to determine the direction of rotation.

This new technology enhances our ability to control the senses. We are now able to directly manipulate vision at a cellular level. Even accounting for the system’s limitations and variability of laser stimulation, the Oz system has precision unlike anything before it. It is possible to reach this level of control because retinas are easily accessible to lasers. However, it would be much more difficult to control other structures that are inaccessible, such as the cochlea or the brain.

It is exciting to think of how neurotechnology in the future will allow us to manipulate the senses. Right now, researchers can only give simple stimuli such as static images of colors/bars or rotating dots. Will we be able to manipulate sight and sound to play whole sequences of events in our minds? Rather than showing novel stimuli, could we replay our memories? Could we fabricate new memories? Neuroscience research is rapidly advancing, and our growing understanding of nervous systems allows us not just to interpret sensory inputs but to reshape them.

#future