Alterations of the contrast gain during normal aging: a dissociation between the Magnocellular and Parvocellular signatures for old and very-old groups

Abstract

Functional changes in normal aging for both Magnocellular (M) and Parvocellular (P) pathways have been reported, with a greater loss for the P system (Elliot & Werner, 2010, JOV). The aim of the study was to investigate the late development of the two systems in old age by comparing two aged groups. A short version of the original paradigm (Pokorny and Smith, 1997, JOSA) has been used in 18 young (19-34), 25 old (61-74) and 11very old (75-80) observers. They had to discriminate the location of the higher luminance square with in a 33-msec four-square-array. In the steady-pedestal condition (M-bias), the array was preceded and followed by a four identical squares pedestal whereas, in the pulse pedestal condition (P-bias), the array was presented alone on a gray background. Three target luminance discrimination thresholds were collected for each of the 6 experimental conditions (order counterbalanced): 3 pedestal-contrasts (63%; 70%; 75%) x 2 pedestal-conditions (pulse and steady) using an adaptive staircase procedure. The results showed a higher increase of threshold when pedestal contrast increased in the pulse-pedestal than in the steady-pedestal condition, consistently with the original results in young adults. The main result was a double interaction between group, pedestal contrast and pedestal-condition : There was a huge increase of threshold with aging in the pulse-pedestal condition, with no differences between the two aged groups, whereas in the steady-pedestal, there was a slight increase in threshold in old age and a larger increase in threshold in the very-old aged group. These results are consistent with a dissociation in the evolution of the two systems with aging. Under the conditions tested, the functional loss for the P pathway, tough larger than the M pathway, seems to be stable from 60-year-old, although the M pathways still deteriorated after 75-year-old. Meeting abstract presented at VSS 2012