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Maka Malania, Frederic Devinck, Joseph L. Hardy, Peter B. Delahunt, Kenneth Knoblauch, John S. Werner; Test of senescent change in photopic spatial summation. Journal of Vision 2009;9(8):1074. doi: 10.1167/9.8.1074.
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Previous research has demonstrated age-related increases in scotopic spatial summation area, correlated with age-related losses in rods and ganglion cells. Grating spatial summation is typically measured in terms of contrast threshold vs. area. As area increases, there is a decrease in contrast threshold up to a critical size, after which there is no further change in contrast threshold. We measured contrast detection thresholds for foveally presented stimuli over a range of sizes in groups of younger (age range 19–20 years) and older (age range 67–83 years) observers. To control for age-related changes in pupil area, the stimuli were presented in a Maxwellian-view optical system. A bite-bar and auxiliary optical system were used to maintain alignment of the pupil with respect to the optic axis of a 2x astronomical telescope. The stimulus was a 76 Troland, vertical, 5 cpd Gabor patch that was increased in area from 0.13 to 12.56 deg2. Threshold for each stimulus area was measured using a two-alternative forced-choice method combined with QUEST adaptive staircase procedure. The data demonstrated a reduction in threshold up to a critical area, and could be fitted with a bilinear function (having slopes of 0.5 and 0 on log-log coordinates) using a least-squares criterion to define spatial summation area (the inflection point of the two functions). Consistent with previous work, we find an age-related increase in contrast detection threshold. In contrast to scotopic conditions, we found that foveal, photopic summation area remains relatively intact with increases in age.
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