It is Brain; Not the Eye by Which We Can See!

Shoubhik Chakraborty, B. Optom

M. Optometry Student, NSHM Kolkata, Paediatric Optometrist, Kalinga Institute of Medical Sciences, Bhuwaneswar, India

The human brain is an incredibly complex and sophisticated organ that plays a central role in the process of vision. While it was previously believed that the occipital lobe was solely responsible for vision, current research has revealed a more intricate and distributed process involving multiple brain regions.

1. Occipital Lobe and Primary Visual Cortex: The occipital lobe, located at the back of the brain, houses the primary visual cortex, responsible for processing basic visual information received from the eyes. Here, the brain analyses the fundamental features of a flying bird, such as its shape, colour, and movement.
2. Distributed Process: Vision is not confined to the occipital lobe alone. Instead, approximately 70% of the brain’s neural connections are dedicated to processing visual information, indicating that multiple brain regions are involved in this essential function. ⁽¹⁾
3. Memory Retrieval in the Temporal Lobe: To identify the bird, the brain accesses stored memory in the temporal lobe, where information about different bird species is stored. This enables us to recognise and differentiate between various types of birds based on past experiences.
4. Involvement of the Frontal Lobe: The frontal lobe, responsible for executive functions, plays a crucial role in tracking the bird’s flight path. It helps predict the bird’s trajectory, allowing us to anticipate its movements and adjust our focus accordingly.
5. Spatial Processing in the Parietal Lobe: The parietal lobe comes into play to judge the bird’s position in space. Through spatial processing, we can perceive the bird’s location relative to our own, giving us a sense of depth and distance.
6. Enhancing Visual Clarity in the Occipital Lobe: The occipital lobe is not limited to basic processing; it also enhances the clarity and contrast of the bird’s image, ensuring that we perceive it sharply.

Figure 1: Involvement of all the lobes of the brain for visual processing
Image reference: Danckert J, Striemer C, Rossetti Y. Blindsight. InHandbook of clinical neurology 2021 Jan 1 (Vol. 178, pp. 297-310). Elsevier.

7. Vision for Action and Perception: When the goal is to catch the flying bird, a more intricate mechanism combining “vision for action” and “vision for perception” is engaged. ⁽²⁾ Visual perception is explained on Figure 1.
8. Dorsal Stream: The dorsal stream, also known as the “where” pathway, connects the occipital, parietal, and frontal lobes. It guides our actions based on visual information, enabling us to reach for and catch the bird with precision.
9. Ventral Stream: The ventral stream, or the “what” pathway, connects the occipital and temporal lobes. It identifies objects and their characteristics, allowing us to recognise the bird and differentiate it from other objects in the environment. ⁽³⁾

In conclusion, vision is a complex and distributed process involving multiple brain regions, with the brain, rather than just the eyes, serving as the primary organ responsible for this essential function. The harmonious collaboration of these brain regions results in our extraordinary ability to perceive and understand the world around us visually. ⁽⁴⁾

References:

1. Zihl, J., & Dutton, G. N. (2016). Cerebral visual impairment in children. Springer Verlag Gmbh.
2. Kaas, J. H., & Lyon, D. C. (2007). Pulvinar contributions to the dorsal and ventral streams of visual processing in primates. Brain research reviews, 55(2), 285-296.
3. Ungerleider, L. G., & Haxby, J. V. (1994). ‘What’and ‘where’in the human brain. Current opinion in neurobiology, 4(2), 157-165.
4. Weiskrantz, L. (2003). Unconscious perception: blindsight. The Neuropsychology of Vision, 283-306.