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Quentin Lenoble, Hélène Amieva, Sandrine Delord; Impairment of Magnocellular and Parvocellular Visual Processing in Normal Aging: Rehabilitation by Yellow Filters or Placebo Effect?. Journal of Vision 2010;10(7):421. doi: 10.1167/10.7.421.
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© ARVO (1962-2015); The Authors (2016-present)
The study aimed at evaluating the psychophysical correlates of the magnocellular and parvocellular visual pathways, their evolution and rehabilitation with normal aging. Thirteen young (24.2) and 36 old (71.4) participants were shown with a short version of the psychophysical paradigm (Pokorny and Smith, 1997, JOSA), to bias processing toward magnocellular or parvocellular processing. Observers had to discriminate the location of the higher luminance square within a 33-msec four-square-array. In the steady-pedestal condition (magnocellular-bias), the array was preceded and followed by a four identical squares pedestal whereas, in the pulse pedestal condition (parvocellular-bias), the array was presented alone on a gray background. There were three filters: a control (no filter), a placebo (neutral filters), and an experimental condition (yellow filters, CPF 450). Three target luminance discrimination thresholds were collected for each of the 18 experimental conditions (order counterbalanced): pedestal-contrast (63%; 70%; 75%) x pedestal-condition (pulse and steady) x filters (no filter, neutral, yellow) using an adaptive staircase procedure. The results showed a higher increase of threshold with pedestal contrast in the pulse-pedestal relative to the steady-pedestal condition. A double interaction between group, pedestal contrast and pedestal-condition was observed: the increased discrimination threshold found for old relative to young participants was stronger in the pulse-pedestal than in the steady-pedestal condition, especially for high pedestal contrasts. Moreover, there was no significant main effect of filter and no interaction between filter and the other variables. However, specifically in the steady-pedestal condition and for old group, planned comparisons showed a significant decrease in threshold for neutral or for yellow filters relative to no filter condition, whatever the pedestal contrast. These results replicate the dissociation between the two low-level visual systems in young group and demonstrate a magnocellular and huge parvocellular impairment with normal aging. The yellow filters were inefficient but a placebo effect was found
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