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R.W. Gagnon, D.W. Kline, G. Jung; Differential Age Effects on Sequential versus Simultaneous Spatial Interval (SI) Discrimination . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5347.
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© ARVO (1962-2015); The Authors (2016-present)
To measure aging effects on cortical visual functioning, monocular and binocular thresholds were determined for sequential and simultaneous versions of Spatial Interval (SI) acuity and SI Same/Different (SD) discrimination.
Two groups, each consisting of 24 healthy observers, refracted to best acuity at the test distance, participated in the study: a young group (M age = 25.3 years) and an old group (M age = 70.8 years). Monocular and binocular SI and SD thresholds were determined for spatial intervals defined by two pairs of light–on–dark (Michelson contrast = .14, line strength = 28.56%min) vertical lines (12.0 by 2.0 minarc). The pairs were presented simultaneously, or sequentially with an ISI of 500ms.
SI and SD thresholds were lower for the young than old observers, and for monocular than binocular viewing (p < .05). SI thresholds were lower for simultaneous than sequential presentation for old (67.7 versus 83.9 arcsec), but not young observers (47.6 versus 50.7 arcsec). SD thresholds were also lower for simultaneous than sequential presentation for old observers (156.3 versus 194.2 arcsec), but not young ones (122.4 versus 133.3 arcsec). The mean sequential/simultaneous difference was about 5 times greater for the old than young observers on the SI task, and about 3.5 times greater on the SD task. Binocular Summation Ratios (BSR = best–eye monocular/binocular threshold) did not vary by age, nor was any evidence seen in either age group or task type for binocular summation beyond probability (p > .05).
Neither SI nor SD manifest binocular summation beyond probability, nor does observer age appear to affect the extent of summation on either task. Aging is associated, however, with a downward trajectory of similar magnitude on the SI and SD tasks. The age–related deficit is more pronounced for targets presented sequentially versus simultaneously, and unrelated to age differences on acuity or contrast sensitivity. Consistent with previous research (Kline & Gagnon, 2005), our findings suggest a pronounced age–related decline in the cortical mechanisms that mediate temporal comparisons of low–contrast spatial intervals. Finally, they extend to older observers the suggestion (e.g., Orban & Vogels, 1998) that cortical engagement is task– rather than attribute–specific, at least for some hyperacuity tasks (e.g., orientation discrimination).
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