Anderson Roger S, Thibos Larry N
Vision Science Research Group, School of Biomedical Sciences, University of Ulster at Coleraine, Northern Ireland, UK.
Spat Vis. 2004;17(1-2):5-15. doi: 10.1163/156856804322778242.
We wished to devise a measure of dissimilarity (D) which could predict psychophysical discrimination performance for Snellen letter pairs in peripheral vision. Threshold size for discriminating 33 pairs of Snellen letters was measured at 30 degrees eccentricity in the nasal retina for two subjects. D was computed for each pair by performing an overlap subtraction in the spatial domain, followed by a Fast Fourier Transform on this difference image, and dividing the total power in the resultant 'difference spectrum' by the sum of the powers of the individual letter spectra. A plot of D vs. psychophysical threshold letter size gave a mean correlation of R = -0.81. When D was calculated for letters that were low-pass filtered at different cut-off frequencies, the correlation with psychophysical performance was greatest when cut-off was between 1.25-1.9 cycles/letter (R = -0.85). Conversely, when the difference spectrum was high-pass filtered at different cut-off frequencies, the correlation decreased continuously as the cut-off increased. These results imply that the band of frequencies between zero and 1.25 cycles/letter are most important for letter discrimination in peripheral vision.
我们希望设计一种差异度量（D），它能够预测周边视觉中斯内伦字母对的心理物理学辨别表现。对两名受试者在鼻侧视网膜30度偏心率处测量了辨别33对斯内伦字母的阈值大小。通过在空间域中进行重叠减法，然后对该差异图像进行快速傅里叶变换，并将所得“差异频谱”中的总功率除以各个字母频谱功率之和，来计算每对字母的D值。D与心理物理学阈值字母大小的关系图的平均相关系数R = -0.81。当对在不同截止频率下进行低通滤波的字母计算D值时，截止频率在1.25 - 1.9周/字母之间时，与心理物理学表现的相关性最大（R = -0.85）。相反，当差异频谱在不同截止频率下进行高通滤波时，随着截止频率的增加，相关性持续下降。这些结果表明，零到1.25周/字母之间的频率带对于周边视觉中的字母辨别最为重要。
