When light from an object enters your eye, it passes through the lens and forms an image on the retina, which is a layer of light-sensitive cells located at the back of your eye. The retina contains two types of photoreceptor cells: rods and cones.
Rods are responsible for vision in low light conditions and are not very sensitive to color. Cones, on the other hand, are responsible for color vision and are most active in bright light. Cones are concentrated in a small region of the retina called the fovea, which is responsible for high-acuity vision and detailed color perception.
When you focus your gaze on a specific object, light from that object falls predominantly on the fovea, where cone cells are densely packed. This allows for detailed color vision and the perception of individual objects.
However, light from the object also falls on other parts of the retina, including areas outside the fovea where the density of cone cells is lower, and rod cells are more prevalent. In these peripheral regions, the sensitivity to color and fine details is reduced, and the visual information is less precise.
Your brain processes the combined input from the rods and cones across the entire retina to create a coherent visual perception. The brain can effectively distinguish between objects based on their spatial location, contrast, and other visual cues, allowing you to perceive individual objects rather than a mixture of colors.
In summary, while light from an object does reach various parts of the retina, your visual system, particularly the fovea, allows you to focus on specific objects and perceive them individually based on the detailed information provided by cone cells in the region where light is most concentrated.