Question

What color do you see when you close your eyes while in a dark room? Explain.

Short answer

The color seen is eigengrau, a very dark gray perceived in absence of light.

Step-by-step solution

Determine the Situation

The exercise asks about the perception of color when eyes are closed in a dark room. It requires analyzing what is seen without external light sources.

Understanding Darkness Perception

When in a completely dark room, there are no photons entering your eyes. This means there is no light to be detected by the photoreceptors in your retina.

Understanding Visual Input When Eyes Are Closed

When you close your eyes, your eyelids block external light. Therefore, even if there were light in the room, it is not detected. In complete darkness and with closed eyes, this lack of light results in the brain interpreting visual input as completely absent.

Exploring Noise in the Visual System

Even when no light is present, your brain can still interpret small amounts of 'visual noise.' This is due to spontaneous activity in your visual system. This noise may sometimes be perceived as a very dim, dark color.

The Concept of 'Eigengrau'

The 'color' perceived in total darkness or when eyes are closed is often referred to as 'eigengrau,' a German term meaning 'intrinsic gray.' This isn't a bright color but rather a very dark gray that is still perceived due to the lack of complete absence of visual experience.

Key concepts

Photoreceptors

Photoreceptors are specialized cells in the retina of the eye responsible for detecting light. They play a crucial role in our ability to see and perceive the world around us. When in a well-lit environment, photons, which are particles of light, enter the eye and interact with these photoreceptors. There are two main types of photoreceptors: rods and cones.

• Rods: These are highly sensitive to light and do not perceive color. They are mainly responsible for vision in low-light conditions.
• Cones: These operate in brighter light conditions and enable us to see colors.

However, when you are in complete darkness or have your eyes closed, as in the given exercise, no photons reach these photoreceptors. As a result, they are not stimulated, and no clear visual signal is sent to the brain. Instead, the brain's perception of any visual input in this situation depends on noise from neural activities within the visual system itself.

Visual Noise

Visual noise is an important concept in understanding what we see when there is no external light source. Even in complete darkness, our brains are not completely silent. Neurons in the visual system can still be active and produce spontaneous signals.

This internal noise is why sometimes, in complete darkness or with our eyes closed, we might perceive faint bits of light or patterns. This experience is not due to any external visual stimuli but rather originates from within the brain itself. Factors contributing to visual noise include:

• Sensory Neurons: Random firing may generate signals interpreted as visual input.
• Imperfect System: The eye and brain's inherent imperfections can lead to minor interpretations of light where there is none.

Therefore, even when photoreceptors are not activated by real light, the brain's interpretation of this internal noise can affect what one "sees" in darkness.

Eigengrau

Eigengrau, also known as "intrinsic gray," is the term used to describe the very dark gray color that one often "sees" in complete darkness or with closed eyes. It's an intriguing phenomenon named from the German words for "own gray."

Eigengrau is not a true color because it is not caused by any actual light perceived by the eyes. Instead, it stems from the visual noise created by the brain's activity in the absence of external visual information. This phenomenon highlights an important aspect of human perception: that it is not merely a passive reception of signals but also involves interpretation by the brain.

• Intrinsic Activity: The brain generates a baseline visual input that it perceives as eigengrau.
• Continuity of Perception: Even without external input, our perception persists to fill in the gaps.

Understanding eigengrau helps explain why total visual blackness is rarely experienced, even in complete darkness, due to the brain's innovative and continuous processing of perceived inputs and its own noise.