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Paper
Link: https://scholar.google.com/citations?user=gyugy60AAAAJ&hl=en&oi=sra
Year:
- There are approximately 1 million retinal ganglion cells (RGCs) in the human retina but their number tends to decrease with aging
- three main RGC types, the Magnocellular projecting cells (M-cells), Parvocellular projecting cells (P-cells) and Koniocellular (K-) cells
- two main classes of primate RGCs, the M-cells and the P-cells
M-cells
- M-cells, also called parasol cells, have larger receptive fields, respond better to large, coarse objects than the P-cells
- M-cells are about two to three times larger in diameter than the P-cells at any given retinal eccentricity
- make up of approximately 10% of the total RGCs
- M-cells are shown to be 8-10 times more sensitive to low achromatic contrast than the small P-cells
- respond somewhat better to high temporal frequencies (motion) and low spatial frequencies
- M-cells are also more sensitive than P-cells to achromatic stimuli
- Since M-cells are relatively fewer in numbers and more sparsely distributed than P-cells, they have less redundancy - there is limited overlapping coverage of the visual field, therefore if for example there is a loss of function just a few of these cells, there will be a location of the VF where there are no cells available to sense the target
- magnocellular pathway cannot provide finely detailed or colored information, but still provides useful static, depth, and motion information (wiki)
- M pathway has high light/dark contrast detection, and is more sensitive at low spatial frequencies than high spatial frequencies (wiki)
P-cells
- or midget cells, project to the four Parvocellular layers of the LGN
- have relatively smaller cell bodies and dendritic trees
- make up of approximately 80% of the total RGCs
- P-cells are relatively more sensitive to low temporal and high spatial frequencies than the M-cells
- respond quite linearly from low to high grating contrasts
- respond best to chromatic especially red or green colours
- parvocellular neurons are sensitive to colour, and are more capable of discriminating fine details than their magnocellular counterparts (wiki)
- Parvocellular cells have greater spatial resolution, but lower temporal resolution, than the magnocellular cells (wiki)
| Parvocellular (P-cells) | Magnocellular (M-cells) |
|---|---|
| Low temporal frequency | High temporal frequency |
| High spatial frequency | Low spatial frequency |
| High contrast threshold | Low contrast threshold (Lee, Wehrhahn et al. 1995) |
| Low contrast gain (low contrast sensitivity); Linear response to 100% (Kaplan and Shapley 1986) | High contrast gain (up to 10 times more than P-cells; Response saturates at 15-20 % contrast (Kaplan and Shapley 1986) |
| Responds more strongly to chromatic than achromatic stimuli especially red/green | Responds best to achromatic stimuli (luminance contrast) |