The 'what pathway,' also known as the perception pathway, is primarily responsible for object recognition and identification. Anatomically, it processes information along a route from the visual cortex to the temporal lobe.

The what pathway (perception pathway)

The 'where/how pathway,' also referred to as the action pathway, is involved in determining an object's location in space and how one might interact with it. This processing stream runs from the visual cortex to the parietal lobe.

The Where/How Pathway (Action Pathway)

Based on the following case study, identify which of the two primary visual processing streams ('what' vs. 'where/how') is most likely impaired. Justify your answer by linking the patient's symptoms to the specific function of that pathway.

Visual Pathway Deficit Analysis

When someone sees a ball rolling down the street, the what pathway identifies the object, while the where/how pathway identifies where it is or how it is moving through space.

Ball Rolling Down the Street in the What and Where/How Pathways

Visual information is processed within the brain through two main parallel pathways. The 'what pathway' is tasked with object recognition and identification. In contrast, the 'where/how pathway' is concerned with an object's location in space and how to interact with it.

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- Visual information is first processed by cells in the retina 
    - photoreceptors, bipolar cells, ganglion cells, horizontal cells, and amacrine cells
- Axons of ganglion cells make up the optic nerve, which transmits this visual information to the lateral geniculate nucleus (LGN) and the superior colliculus of the brain
- Neurons of the LGN synapse on the primary visual cortex, in the occipital lobe

Neural signals from the eye to the brain

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

- The retina projects its information in a map-like manner
- The information stays this way as it passes through different regions of the brain
- Because of this, deficits in visual perception can be determined based on where damage is in the visual pathway or the brain
    - Scotomas are these regions of blindness

Retinotopic mapping

There are two types of photoreceptors in the eye: rods and cones. They are light-sensitive receptors. Rods are most active when there is dim lighting. Cones are most active when there is bright lighting, and can detect color.

Photoreceptors

- The LGN is a part of the thalamus that transmits visual information
- Receives information from the optic tract
- Sends information to the occipital lobe
- Some axons terminate in the primary visual cortex of the occipital lobe-- these are called optic radiations

Lateral geniculate nucleus (LGN)

- Optic nerve transmits signals to the superior colliculus
- Controls quick movements of the eye to look at a specific target 
- Helps control pupil size

Superior colliculus role in vision

The optic nerve is a bundle of nerve fibers formed by the convergence of axons from retinal ganglion cells. It exits through the back of the eye and serves as the primary pathway for transmitting visual information from the retina to the brain.

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