Simple cortical cells: 
- Respond best to an edge or line with a particular width, orientation, and location in the visual field
- Receive input from a group of LGN cells
- Respond best to a bar of light

Complex cortical cells:
- Respond best to an edge or line with a particular width and orientation anywhere within a larger area of the visual field 
- Recieve input from a group of simple cortical cells
- Respond best to a moving bar of light

Receptive fields of cortical cells

These cells can be categorized by which types of stimuli they are most sensitive to. The two main categories are simple cortical cells and complex cortical cells.

University of Michigan - Ann Arbor

- Neurons in the visual cortex require more specific stimulation than neurons of the LGN
- Different groups of neurons here have different receptive fields
- Some respond best to movement, some to lines in a particular orientation, and many others

Complex receptive fields of visual cortex neurons

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

Behavioral Neuroscience 8th Edition

Categorization of cortical cells

- In addition to perceiving objects and events, this area of the visual cortex is necessary for the formation of mental images
- Areas of V1 light up on PET scan when participants imagine mental images, showing activation of those areas
- Repetitive transcranial magnetic stimulation (rTMS) impairs activation of specific parts of the brain
    - When rTMS is administered to V1, ability to form mental images is greatly impaired

V1 area's role in formation of mental images

- Area V1 sends signals to other parts of the visual cortex
- Areas of the visual cortex outside of V1 have even more complex receptive fields
    - V2, V4, and the inferior temporal area are involved in the perception of form
    - Some V2 cells respond to texture and some respond to imagined contours or edges, such as in optical illusions
    - Some V4 cells respond best to wavelength differences, producing color perception
    - Area V5 responds to the perception of movement
- Macaque monkeys have at least 32 different cortical areas involved in vision, with a similar layout to the human brain

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