Scientists have recently clarified why our eyes sometimes register colors that are not truly present. This effect, commonly known as color afterimage, occurs when we fixate on a true color for an extended period and then perceive false, illusory hues in the following image.
The root of this illusion lies in the brain’s ability to maintain color constancy throughout a day, ensuring that the environment’s perceived colors remain consistent despite variations in light—whether we are bathed in yellow sunlight, under a green canopy, or shaded by bluish light.
For many years, researchers have debated the underlying cause of color afterimages and how the brain generates them.
Associate Professor of Psychology Dr. Christoph Witzel at the University of Southampton has identified the missing link between the illusory colors we experience and the neural processes that produce them. His research, published in the journal Communications Psychology, points to the cone photoreceptor cells in the eye as the critical mechanism.
Dr. Witzel noted, “Color afterimages have long been recognized, yet they remain a source of confusion in both expert circles and educational materials.”
He added, “Some argue that afterimages result from signals in the cone cells, while others propose that neural pathways generate opposing colors, or that a still‑unknown brain mechanism is at play.”
“The conclusive evidence is that afterimages arise from the cones, not opposing colors,” Dr. Witzel explained.
To determine the origin of afterimages within the visual system, Dr. Witzel conducted extensive experiments. He developed custom methods to assess the precise colors people perceive in afterimages and tested three distinct hypotheses.
In one study, 50 participants stared at a chosen “starter” color and then immediately matched the color they saw afterward. In a second experiment, 10 participants repeatedly adjusted the hue of sustained afterimages 360 times on a specialized display.
These empirical measurements were compared against computational models representing various stages of neural processing – from the photoreceptors to intermediary brain structures such as the thalamus, and ultimately the visual cortex.
“Across all experiments, the afterimage colors matched predictions based on cone adaptation,” Dr. Witzel reported. “This confirms that cone cells, rather than other visual pathways, are responsible for the phenomenon.”
He emphasized, “While color afterimages are not a new discovery, this extensive dataset provides a complete and coherent explanation for the first time, bridging gaps in our understanding of ocular and cerebral interactions.”