Metamorphopsia and letter recognition.
Metamorphopsia and letter recognition.
复制标题
视觉变形和字母识别。
DOI：
10.1167/14.14.1
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发表时间：
2014
影响因子：
1.8
通讯作者：
Bex,Peter
中科院分区：
文献类型：
--
作者：
Wiecek,Emily;Dakin,StevenC;Bex,Peter
敏锐度是最常用的视觉功能测量，敏锐度的降低与大多数眼部疾病有关。视物变形-视觉空间的感知扭曲-是视觉障碍的另一种常见症状，目前使用Amsler（1953）图表进行定性评估。为了量化视物变形对敏锐度的影响，我们测量了物理空间失真对字母识别的影响。在早期的工作表明，字母识别被调谐到特定的空间频率（SF）通道，我们假设失真的影响可能取决于视觉失真的空间尺度，就像它取决于掩蔽噪声的空间尺度。6名视力正常的观察员在5个不同的观察距离下完成了26个交替强迫选择（AFC）Sloan字母识别任务，这些字母经历了不同程度的空间失真。使用空间带通滤波的噪声来控制失真，所述空间带通滤波的噪声在空间上重新映射像素位置。噪声在五个空间频率和五个幅度上变化。使用逻辑回归对性能进行建模，并且随着失真幅度的增加和字母大小的减小而线性恶化。我们发现，视网膜SF影响在中频失真，可以解释与调谐的基本对比敏感度函数，而对象为中心的失真SF遵循类似的模式，字母对象识别灵敏度和调谐到大约三个周期每字母（CPL）。字母大小和失真之间的相互作用使得视物变形评估的敏锐度结果不可靠。
Acuity is the most commonly used measure of visual function, and reductions in acuity are associated with most eye diseases. Metamorphopsia—a perceived distortion of visual space—is another common symptom of visual impairment and is currently assessed qualitatively using Amsler (1953) charts. In order to quantify the impact of metamorphopsia on acuity, we measured the effect of physical spatial distortion on letter recognition. Following earlier work showing that letter recognition is tuned to specific spatial frequency (SF) channels, we hypothesized that the effect of distortion might depend on the spatial scale of visual distortion just as it depends on the spatial scale of masking noise. Six normally sighted observers completed a 26 alternate forced choice (AFC) Sloan letter identification task at five different viewing distances, and the letters underwent different levels of spatial distortion. Distortion was controlled using spatially band-pass filtered noise that spatially remapped pixel locations. Noise was varied over five spatial frequencies and five magnitudes. Performance was modeled with logistic regression and worsened linearly with increasing distortion magnitude and decreasing letter size. We found that retinal SF affects distortion at midrange frequencies and can be explained with the tuning of a basic contrast sensitivity function, while object-centered distortion SF follows a similar pattern of letter object recognition sensitivity and is tuned to approximately three cycles per letter (CPL). The interaction between letter size and distortion makes acuity an unreliable outcome for metamorphopsia assessment.