Dr. David Berson on Huberman Lab: Why Eyes Do More Than See

Human retinas typically have three cone types, each with a different light-sensitive protein tuned to distinct wavelength ranges. The brain compares activity across these three channels to infer the wavelength composition of light, producing the subjective experience of color. Most mammals (like dogs and cats) have only two cone types, which limits their color range, while additional pigments (rods and melanopsin) support low-light vision and brightness detection rather than color.

Some ganglion cells in the innermost retina are directly light-sensitive via melanopsin, acting as brightness sensors rather than image-forming detectors. They project to the suprachiasmatic nucleus (SCN) in the hypothalamus—the central circadian pacemaker—which in turn influences hormones (e.g., melatonin via the pineal gland) and the autonomic nervous system. Bright light at night, even briefly (like turning on bathroom lights), can sharply suppress melatonin, immediately shifting hormonal status and potentially disturbing sleep.

The vestibular system in the inner ear senses head and body acceleration via fluid moving over hair cells in three oriented semicircular canals. Normally, vestibular signals and visual motion agree (e.g., driving while looking at the road). When they conflict—such as when your body accelerates in a car but your eyes are fixed on a stable phone screen—the brain receives incompatible movement reports from the two systems. This “visual–vestibular conflict” can trigger nausea as a kind of behavioral punishment signal that nudges you to change your behavior (e.g., look outside instead of at the phone).

Rapid head rotations trigger a reflex where the eyes automatically move in the opposite direction, even in complete darkness, to keep the visual scene stable on the retina. Animals like pigeons and chickens show dramatic head-stabilizing behaviors that serve the same purpose. A specialized cerebellar region (the flocculus) integrates visual and vestibular input and performs ongoing error correction, learning to compensate when the vestibular apparatus is damaged by boosting or adjusting signals to maintain image stability and precise movements.

The superior colliculus (tectum) in the midbrain receives visual, auditory, tactile, and even specialized inputs (like infrared heat sensing in rattlesnakes). It rapidly orients gaze, head, and sometimes body toward or away from salient events without conscious deliberation—for example, reflexively looking at a sudden movement or splat on a page. It exemplifies how the brain treats all sensory inputs as electrical signals that are combined to estimate “what is where,” enhancing reliability when they agree and potentially causing confusion or discomfort when they conflict.