Effects of aging on shape discrimination.
A large number of senior patients manifest eye diseases in addition to normal aging changes in their visual system. Visual tests not affected by age would be very useful in early detection of age-related eye diseases. The purpose of this study was to determine the effects of aging on the detection of contour deformation. Seventy-six normal subjects were divided into three age groups: young adults 15 to 39 years old (N = 26); middle-aged adults 40 to 59 years old (N = 22); and senior adults 60 to 78 years old (N = 28). Stimuli were circular or linear D4 (4th derivative of Gaussian) contours. A spatial two-alternative forced-choice staircase paradigm was used. In each trial, one deformed and one undeformed contour were presented on a screen. Subjects indicated which contour was deformed. Deformation detection thresholds were estimated by a maximum likelihood fitting procedure. We found that at a low modulation frequency (four cycles), the performance of detecting deformation does not change with age, and it does not correlate with either visual acuity or letter contrast sensitivity. At a higher modulation frequency (eight cycles), a significant difference between mean thresholds was found for young and senior adults. For circular D4, the mean threshold was elevated by 18%, from 7.6 sec arc (young adults) to 9.0 sec arc (senior adults). For linear D4, the mean threshold was elevated by 52%, from 5.8 sec arc to 8.8 sec arc. As a comparison, minimum angle of resolution was increased by 33%, and letter contrast threshold was elevated by 81%. The performance for linear D4 at higher modulation frequency was found to be significantly correlated with contrast threshold. These results provide further evidence to support the hypothesis that different mechanisms may be underlying the detection of circular and linear D4 contour deformation. The very small effect of aging on hyperacuity for radial deformation suggests that a global shape discrimination task could be a sensitive test for quantifying the early visual loss caused by eye diseases among seniors.
Wang
Y Z
YZ
Retina Foundation of the Southwest and Department of Ophthalmology, UT Southwestern Medical Center, Dallas, Texas 75231, USA. yiwang@retinafoundation.org
D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D014787:Vision Tests; D014792:Visual Acuity