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Clinical Psychophysical Assessment of the ON- and OFF-Systems of the Magnocellular and Parvocellular Visual Pathways

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Author(s): Marcelo Fernandes Costa

Journal: Neuroscience & Medicine
ISSN 2158-2912

Volume: 02;
Issue: 04;
Start page: 330;
Date: 2011;
Original page

Keywords: Visual Perception | Visual Pathway | Contrast Sensitivity | Psychophysics

ABSTRACT
We developed a psychophysical paradigm for the clinical assessment of the contrast sensitivity (CS) mediated by the ON- and OFF-systems of the Magnocellular and Parvocellular pathways. We designed a stimulus considering two dimensions: two spatial frequencies (0.5 and 4.5 cpd) and two temporal rates of flicker (33 ms and 1500 ms). To evidence the ON- and OFF responses, the CS was measured for two polarities of light with luminance changes of 0.6 dB steps above and below the medium luminance grey background. We tested 38 healthy volunteers. The results shows that Magnocellular contrast sensitivity was higher than Parvocellular for the 33 ms flickering stimulus and the Parvocellular contrast sensitivity was higher than Magnocellular for 1500 ms stimuli. The reliability of the test was checked and confirmed. We concluded that the test performs a rapid measurement of the CS mediated by the ON and OFF systems of Magnocellular and Parvocellular pathways. It is useful in clinical protocols due to its high sensitivity and good reliability.
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