Spatial-frequency characteristics of letter identification in central and peripheral vision
Spatial-frequency characteristics of letter identification in central and peripheral vision
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DOI：
10.1016/s0042-6989(02)00092-5
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发表时间：
2002-08-01
期刊：
影响因子：
1.8
通讯作者：
Tjan, BS
中科院分区：
文献类型：
--
作者：
Chung, STL;Legge, GE;Tjan, BS
字母识别的空间-频率特征在中央凹中比在周边更好地理解。本研究的目的是比较中央视觉和周边视觉中字母识别的空间频率特性。我们测量了对比度阈值，用于识别单个，时间罗马小写字母，空间带通滤波。26个字母中的每一个都用一组9个余弦对数滤波器进行数字滤波，峰值对象空间频率范围从0.63到10 c/字母，以半倍频程为步长。滤波器的带宽为I倍频程。3名视力正常的观察者分别在中心凹、下视野5 °和10 °处进行单眼测试。字母大小分别为0.2，0.4和0.6对数单位大于高对比度，未过滤的敏锐度字母。字母识别的对比灵敏度与带通滤波器的频率的关系图显示了空间调谐。一般来说，字母识别的空间频率特性在中央视觉和周边视觉之间基本相同。这些特性包括空间调谐函数的峰值频率随字母大小和调谐函数的带宽的缩放。中央凹和周边之间的唯一区别是，对于相同的物理字母大小，空间调谐功能的峰值灵敏度在中央凹处比在周边处发生在更高的视网膜频率处。为了测试对比敏感度函数（CSF）是否可以解释中央视觉和周边视觉之间字母识别的空间频率特性的差异，我们将人类CSF纳入理想观察者模型，并测试该理想观察者在与人类观察者相同的字母识别任务上的表现。从这个CSF理想的观察员的数据非常相似的人类观察员，这表明人类字母识别的空间频率特性可以占CSF和字母身份信息，而不调用窄带空间频率通道之间的选择。(C)2002爱思唯尔科技有限公司。保留所有权利。
Spatial-frequency characteristics of letter identification are much better understood in the fovea, than in the periphery. The purpose of this study was to compare the spatial-frequency characteristics of letter identification in central and peripheral vision. We measured contrast thresholds for identifying single, Times-Roman lower-case letters that were spatially band-pass filtered. Each of the 26 letters was digitally filtered with a set of nine cosine log filters, with peak object spatial frequencies ranging from 0.63 to 10 c/letter, in half-octave steps. Bandwidth of the filters was I octave. Three observers with normal vision were each tested monocularly at the fovea, and at 5degrees and 10degrees in the inferior visual field. Letter sizes were 0.2, 0.4 and 0.6 log units larger than high contrast, unfiltered acuity letters. Plots of contrast sensitivity for letter identification vs. frequency of the band-pass filters exhibit spatial tuning. In general, the spatial-frequency characteristics of letter identification are fundamentally identical between central and peripheral vision. These characteristics include the scaling of the peak frequency of the spatial-tuning functions with letter size and the bandwidth of the tuning functions. The only difference between the fovea and the periphery is that for the same physical letter size, peak sensitivity of the spatial-tuning functions occurs at a higher retinal frequency at the fovea than in the periphery. To test whether or not the contrast sensitivity function (CSF) can account for the differences in the spatial-frequency characteristics of letter identification between central and peripheral vision, we incorporated a human CSF into an ideal-observer model, and tested the performance of this ideal-observer on the same letter identification task used with the human observers. Data from this CSF-ideal-observer resemble closely those of human observers, suggesting that the spatial-frequency characteristics of human letter identification can be accounted for by the CSF and the letter-identity information, without invoking selection among narrow-band spatial-frequency channels. (C) 2002 Elsevier Science Ltd. All rights reserved.