Our ability to see and interact with the world through our eyes is a complex feat orchestrated by the brain. It is not a single command center that manages this process, but rather an intricate network of specialized areas working in concert. This distributed control allows for the rapid processing of visual information and the precise coordination of eye movements, forming the foundation of our visual experience.
Processing What You See
The initial steps of visual processing begin as light enters the eyes and strikes the retina, converting light into electrical signals. These signals then travel along the optic nerves to a relay station deep within the brain called the lateral geniculate nucleus (LGN), located in the thalamus. The LGN acts as a filter, organizing and refining visual information before transmitting it to the brain’s main visual processing areas. This nucleus receives feedback connections from the primary visual cortex, modulating the visual signals.
From the LGN, visual data is sent to the primary visual cortex (V1), which resides in the occipital lobe at the back of the brain. V1 is the first cortical area to receive visual input and is organized in a retinotopic manner, meaning the spatial layout of what you see is preserved in its neural representation. Here, the brain begins to deconstruct the raw visual input, processing features such as lines, edges, orientation, and color. This analysis in V1 prepares the brain for more complex visual interpretations.
Directing Eye Movements
Beyond processing what we see, the brain orchestrates eye movements. Voluntary eye movements, such as intentionally shifting your gaze to a new object, involve the frontal eye fields (FEF) located in the frontal cortex. The FEF plays a role in controlling visual attention and initiating various types of eye movements, including saccades, which are rapid shifts of gaze.
The superior colliculus, located in the midbrain, is involved in orienting the eyes and head towards stimuli. Its superficial layers receive visual input for rapid detection, while deeper layers integrate visual, auditory, and somatosensory information. This integration allows the superior colliculus to play a role in generating saccades and orienting attention.
The brainstem nuclei serve as a final pathway for all types of eye movements, controlling the extraocular muscles. These nuclei are responsible for the various types of eye movements, including saccades, smooth pursuit (tracking a moving object), and vergence (adjusting eye position to maintain focus on objects at different depths). The cerebellum, often called the “little brain,” plays a coordinating role, fine-tuning eye movements for accuracy and smooth performance, ensuring precise and well-calibrated movements that contribute to stable vision and effective tracking of objects.
Making Sense of Visual Information
After initial processing, visual information diverges into two main pathways for higher-level interpretation: the ventral stream and the dorsal stream. The ventral stream, often referred to as the “what” pathway, travels towards the temporal lobe and is involved in object recognition and identification. This pathway allows us to recognize faces, identify objects, and understand their forms. Damage to this stream can impair the ability to recognize objects despite intact basic vision.
The dorsal stream, known as the “where” or “how” pathway, projects towards the parietal lobe. This pathway processes spatial information, understanding object location in space and guiding actions. It helps with spatial awareness, guiding movements like reaching for an object, and integrating visual input with body position. These two streams work together, integrating visual input with memory and other sensory information to construct a comprehensive understanding of our surroundings.