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J Vis. 2010 Apr 13;10(4):4.1-15. doi: 10.1167/10.4.4.

Age-related changes in contrast gain related to the M and P pathways.

Author information

1
Department of Ophthalmology & Vision Science, University of California-Davis, 4860 Y Street, Sacramento, CA 95817, USA. slelliott@ucdavis.edu

Abstract

Neural contributions to the age-related reduction in spatial vision are incontrovertible. Whether there are differential age-related changes in the magnocellular (M) and parvocellular (P) pathways across the life span has not been tested extensively. We studied psychophysically the contrast gain signature of the M and P pathways for 13 younger and 13 older observers. Two separate paradigms thought to separate the M and P pathways based on their contrast gain (J. Pokorny & V. C. Smith, 1997) signature were used. A four-square array was presented as an increment or decrement on a background of 115 Td for 35 ms, with one test square presented at a slightly higher or lower retinal illumination. Using a four-alternative forced-choice procedure, the observer's task was to choose the unique square. The two paradigms differed only in the pretrial adaptation and inter-stimulus array. Data were fitted with models of contrast discrimination derived from the unique contrast gain signatures. The fitted models indicate a change in the discrimination functions with age for both the M and P pathways, revealing a shift in the contrast gain slope. Results indicate that both M and P pathways undergo age-related changes, but functional losses appear greater for the P pathway under the conditions tested.

PMID:
20465324
PMCID:
PMC2872115
DOI:
10.1167/10.4.4
[Indexed for MEDLINE]
Free PMC Article

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