VISION AND READING
There are important pre-attentive processes involving the magnocellular (in particular) & parvocellular subdivisions of the visual system
Start by reviewing some interesting symptoms noted by disabled readers. These related to the illusory text movement phenomenon noted as a symptoms of ocular motor dysfunction.
blurriness
blanching
channels
swirling
low contrast /
glare
Now look at the anatomy of Magno and parvo pathways
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From this summary of the anatomical pathways of the two systems, the P pathway terminates in inferior temporal cortex, the area of the brain that is responsible for identification processes; whereas, the M pathway terminates in the superior temporal cortex and the posterior parietal lobes. These areas are essential for motion detection and object localization.
Therefore, one can conceptualize the P pathway as the "what" system and the M pathway as the "where" system |
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The chart illustrates the distribution of M and P ganglion cells in the retina. Note that the M pathway is gnerally more predominant ine periphery; P cells in the foveal area |
Physiological properties of m and p cells
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Note on the left that M cells have larger receptive fields than P cells and accordingly on the right have a lower cutoff spatial frequency and the maximum contrast sensitivity is found at a lower spatial frequncy than P cells. One can conclude that P cells "see" the higher spatial frequencies of a visual stimulus and the M cells are more sensitive to lower. |
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This illustrates the differences between M and P cells when they "look" at a picture of you know who. |
M&P
Physiological functions Magnocellular Parvocellular transient responses sustained responses higher contrast sensitivity - low spatial frequencies faster achromatic color vision channel motion detection visual acuity - high spatial frequencies inhibits the parvo system