The occipital lobe is generally held to be “the” visual center of the brain, but this is a misnomer. In the previous blog we discussed the fact that the occipital lobe is only one of many visual centers of the brain. Here is a classic graphic of the visual or “V” areas of the brain thought to be geographically within the occipital lobe.
The functional specificities of these areas aren’t clear cut, nor are their geographical boundaries, as beautifully reviewed in this article by Nancy Kanwisher. There’s even a “V” area whose nationality in the occipital lobe can be questioned, V5 also known as area MT – meaning that neuroanatomists can’t quite decided if it’s part of temporal lobe or the occipial lobe (kind of like the twin cities of Minneapolis/St. Paul).
The idea of multiple visual centers in the brain, beyond the occipital lobe, has been acknowledged for many years. An intriguing book as part of a sensory physiology series published by Springer 45 years ago addressed multiple and varied visual centers in the brain beyond the occipital lobe. This included chapters on “The Parietal Eye”, “Visual Functions of the Inferotemporal Cortex”, and “The Role of the Superior Colliculus and Pretectum in Vision and Visually Guided Behavior”. The neuroanatomy of the colliculi makes it clear how intimately they are nestled within the four major lobes of the brain. Along with the pulvinar, the superior colliculus is a crucial midbrain structure traffic-conrolling attention signals within the four lobes of the brain.
Piggybacking on the who/what/where/why/how of the previous blog, the four lobes can be conveniently differentiated as follows. The occipital lobe is primarily dedicated toward processing visual features supportive of object or person identification, such as clarity, color, contour, and contrast to address “who” and “what” issues.
The parietal lobe primarily houses visual centers addressing centering or “where” issues, including locations of objects in space, brain maps, and the interrelationship between self and the rest of the world.
The temporal lobe is primarily dedicated toward timing or temporal elements of vision in contrast with its spatial dimensions. It is a center for auditory-visual integration within the realm of speech-language functions.
And the last of the “The Big Four” is the frontal lobe, which contains the frontal eye fields and parietal eye fields dedicated to “how” and “why” of visual cognition and the directing of where and when to move the eyes. The hub of visual thinking, it is an integral component of executive function filtering information to and from the eyes.
Vision is not located within the eyes, and eyes are not the exclusive purveyors of sight. Eyes are necessary but not sufficient for vision. So we understand that vision occurs in the brain – but where in the brain? It turns out the answer is … everywhere.