Astle Andrew T, Blighe Alan J, Webb Ben S, McGraw Paul V
Visual Neuroscience Group, School of Psychology, University of Nottingham, Nottingham, United Kingdom.
Invest Ophthalmol Vis Sci. 2014 Jul 1;55(8):5039-45. doi: 10.1167/iovs.14-14181.
Crowding describes the increased difficulty in identifying a target object when it is surrounded by nearby objects (flankers). A recent study investigated the effect of age on visual crowding and found equivocal results: Although crowded visual acuity was worse in older participants, crowding expressed as a ratio did not change with age. However, the spatial extent of crowding is a better index of crowding effects and remains unknown. In the present study, we used established psychophysical methods to characterize the effect of age on visual crowding (magnitude and extent) in a letter recognition task.
Letter recognition thresholds were determined for three different flanker separations in 54 adults (aged 18-76 years) with normal vision. Additionally, the spatial extent of crowding was established by measuring spacing thresholds: the flanker-to-target separation required to produce a given reduction in performance. Uncrowded visual acuity, crowded visual acuity, and spacing thresholds were expressed as a function of age, avoiding arbitrary categorization of young and old participants.
Our results showed that uncrowded and crowded visual acuities do not change significantly as a function of age. Furthermore, spacing thresholds did not change with age and approximated Bouma's law (half eccentricity).
These data show that crowding in adults is unaffected by senescence and provide additional evidence for distinct neural mechanisms mediating surround suppression and visual crowding, since the former shows a significant age effect. Finally, our data suggest that the well-documented age-related decline in peripheral reading ability is not due to age-related changes in visual crowding.
拥挤现象是指当目标物体被附近物体（侧翼干扰物）包围时，识别该目标物体的难度增加。最近一项研究调查了年龄对视觉拥挤的影响，结果并不明确：尽管老年参与者的拥挤视力较差，但以比率表示的拥挤程度并未随年龄变化。然而，拥挤的空间范围是衡量拥挤效应的更好指标，目前尚不清楚。在本研究中，我们使用既定的心理物理学方法，在字母识别任务中表征年龄对视觉拥挤（程度和范围）的影响。
在54名视力正常的成年人（年龄18 - 76岁）中，针对三种不同的侧翼干扰物间距确定字母识别阈值。此外，通过测量间距阈值来确定拥挤的空间范围：为使表现下降给定程度所需的侧翼干扰物与目标的间距。未受拥挤的视力、受拥挤的视力和间距阈值均表示为年龄的函数，避免对年轻和老年参与者进行任意分类。
我们的结果表明，未受拥挤和受拥挤的视力不会随年龄显著变化。此外，间距阈值不随年龄变化，且近似于布马定律（半偏心率）。
这些数据表明，成年人的拥挤现象不受衰老影响，并为介导周围抑制和视觉拥挤的不同神经机制提供了额外证据，因为前者显示出显著的年龄效应。最后，我们的数据表明，外周阅读能力与年龄相关的下降有据可查，这并非由于视觉拥挤的年龄相关变化所致。
