Latham K, Barrett B T
Vision Sciences, Aston University, Birmingham, UK.
Curr Eye Res. 1998 Oct;17(10):1010-7. doi: 10.1076/ceyr.17.10.1010.5237.
Performance on positional acuity tasks exhibits marked resistance to the effects of optical image degradation. This places positional acuity tasks in a unique position for psychophysical examination of the effects of age upon visual performance because any observed age-related changes reflect losses in retinal/neural function. One positional acuity task with important consequences for "real-world" vision is spatial interval discrimination, a task in which the subject is required to detect changes in the size of the gap between two objects. In the present study we examine spatial interval discrimination in young and elderly observers as a function of separation and eccentricity.
Stimuli were two Gaussian-modulated luminance patches placed side by side around an imaginary iso-eccentric arc in the upper visual field, allowing eccentricity and separation to be varied independently. Changes in separation were achieved by moving the stimuli around the arc, while eccentricity was varied by changing the radius of the arc. Thresholds were obtained for healthy young and elderly observers using a forced-choice method of constants at two eccentricities (1.25 degrees and 10 degrees) and five separations.
When thresholds, expressed as Weber fractions, are plotted as a function of the geometric ratio of the stimuli (separation/eccentricity) the data from the young and elderly groups collapse to a single function. Performance is independent of age and eccentricity, and depends only on the geometric ratio of the stimuli.
No effect of age was found for spatial interval discrimination. Our results suggest that spatial interval discrimination belongs to the wider group of positional acuities whose neural substrates are unaffected by ageing.
位置敏锐度任务的表现对光学图像退化的影响具有显著抗性。这使得位置敏锐度任务在心理物理学检查年龄对视觉表现的影响方面处于独特地位，因为任何观察到的与年龄相关的变化都反映了视网膜/神经功能的损失。对“现实世界”视力有重要影响的一项位置敏锐度任务是空间间隔辨别，在该任务中，受试者需要检测两个物体之间间隙大小的变化。在本研究中，我们将年轻和年长观察者的空间间隔辨别作为分离度和偏心率的函数进行研究。
刺激物是两个高斯调制的亮度斑块，并排置于上视野中围绕一条假想的等偏心率弧线，从而使偏心率和分离度能够独立变化。通过在弧线上移动刺激物来实现分离度的变化，而通过改变弧线半径来改变偏心率。使用恒定刺激的迫选法，在两个偏心率（1.25度和10度）和五个分离度条件下，获取健康年轻和年长观察者的阈值。
当以韦伯分数表示的阈值作为刺激物的几何比率（分离度/偏心率）的函数进行绘制时，年轻组和年长组的数据汇聚为一个单一函数。表现与年龄和偏心率无关，仅取决于刺激物的几何比率。
未发现年龄对空间间隔辨别有影响。我们的结果表明，空间间隔辨别属于更广泛的位置敏锐度类别，其神经基质不受衰老影响。
