Greenlee M W
Abteilung für Neurophysiologie, Universität Freiburg, Fed. Rep. Germany.
Vision Res. 1992 Feb;32(2):275-83. doi: 10.1016/0042-6989(92)90138-9.
Two experiments were conducted to explore the ability of human observers to discriminate the spatial frequency of briefly-presented, Gaussian-truncated sinewave gratings. In the first experiment, the influence of stimulus contrast and stimulus bandwidth on discrimination thresholds was measured after removing any position cues by randomizing the spatial phase of the gratings for each presentation. In a second experiment, the influence of retinal eccentricity on discrimination thresholds was explored for Gaussian-truncated gratings of constant spatial frequency bandwidth (0.5 octave) and suprathreshold contrast value (5 x detection threshold). The spatial frequency of the reference gratings varied from 1 to 8 c/deg. The gratings were positioned centered at the fixation point or 1-20 deg eccentric of the point of fixation along the horizontal meridian. Two observers responded in a two-interval forced-choice paradigm, which of two gratings had a higher spatial frequency. A difference frequency was randomly added to or subtracted from the spatial frequency of either the first or second grating. Using a maximum-likelihood algorithm, the spatial-frequency discrimination threshold delta f was computed from 40 trials, at which the observer responded with 75% accuracy. The results indicate that discrimination thresholds increase with (1) decreasing stimulus contrast, (2) increasing stimulus bandwidth, and (3) increasing retinal eccentricity. It is shown that spatial-frequency discrimination thresholds are only independent of contrast for narrow bandwidth stimuli having a contrast greater than 0.02. The eccentricity-dependent increase in discrimination thresholds varies with reference spatial frequency: with increasing retinal eccentricity delta f/f increases gradually for low spatial frequencies but rapidly for high spatial frequencies.
进行了两项实验，以探究人类观察者辨别短暂呈现的高斯截断正弦波光栅空间频率的能力。在第一个实验中，通过在每次呈现时随机化光栅的空间相位来消除任何位置线索后，测量刺激对比度和刺激带宽对辨别阈值的影响。在第二个实验中，针对具有恒定空间频率带宽（0.5倍频程）和超阈值对比度值（5倍检测阈值）的高斯截断光栅，探究视网膜离心率对辨别阈值的影响。参考光栅的空间频率在1至8周/度之间变化。光栅位于以注视点为中心或沿水平子午线在注视点偏心1至20度处。两名观察者以二区间强迫选择范式做出反应，判断两个光栅中哪个具有更高的空间频率。一个差异频率被随机加到第一个或第二个光栅的空间频率上或从其减去。使用最大似然算法，从40次试验中计算出空间频率辨别阈值δf，此时观察者的反应准确率为75%。结果表明，辨别阈值随着（1）刺激对比度降低、（2）刺激带宽增加和（3）视网膜离心率增加而升高。结果表明，对于对比度大于0.02的窄带宽刺激，空间频率辨别阈值仅与对比度无关。辨别阈值随离心率的增加因参考空间频率而异：随着视网膜离心率增加，低空间频率时δf/f逐渐增加，而高空间频率时迅速增加。
