Barboni M T S, Gomes B D, Souza G S, Rodrigues A R, Ventura D F, Silveira L C L
Universidade de São Paulo, Instituto de Psicologia, São Paulo, SP, Brasil.
Braz J Med Biol Res. 2013 Feb;46(2):154-63. doi: 10.1590/1414-431x20122428. Epub 2013 Feb 1.
The purpose of the present study was to measure contrast sensitivity to equiluminant gratings using steady-state visual evoked cortical potential (ssVECP) and psychophysics. Six healthy volunteers were evaluated with ssVECPs and psychophysics. The visual stimuli were red-green or blue-yellow horizontal sinusoidal gratings, 5° × 5°, 34.3 cd/m2 mean luminance, presented at 6 Hz. Eight spatial frequencies from 0.2 to 8 cpd were used, each presented at 8 contrast levels. Contrast threshold was obtained by extrapolating second harmonic amplitude values to zero. Psychophysical contrast thresholds were measured using stimuli at 6 Hz and static presentation. Contrast sensitivity was calculated as the inverse function of the pooled cone contrast threshold. ssVECP and both psychophysical contrast sensitivity functions (CSFs) were low-pass functions for red-green gratings. For electrophysiology, the highest contrast sensitivity values were found at 0.4 cpd (1.95 ± 0.15). ssVECP CSF was similar to dynamic psychophysical CSF, while static CSF had higher values ranging from 0.4 to 6 cpd (P < 0.05, ANOVA). Blue-yellow chromatic functions showed no specific tuning shape; however, at high spatial frequencies the evoked potentials showed higher contrast sensitivity than the psychophysical methods (P < 0.05, ANOVA). Evoked potentials can be used reliably to evaluate chromatic red-green CSFs in agreement with psychophysical thresholds, mainly if the same temporal properties are applied to the stimulus. For blue-yellow CSF, correlation between electrophysiology and psychophysics was poor at high spatial frequency, possibly due to a greater effect of chromatic aberration on this kind of stimulus.
本研究的目的是使用稳态视觉诱发电位（ssVECP）和心理物理学方法测量对等亮度光栅的对比敏感度。对6名健康志愿者进行了ssVECP和心理物理学评估。视觉刺激为红-绿或蓝-黄水平正弦光栅，尺寸为5°×5°，平均亮度为34.3 cd/m²，以6 Hz的频率呈现。使用了从0.2到8 cpd的8个空间频率，每个频率以8个对比度水平呈现。通过将二次谐波幅度值外推至零来获得对比度阈值。使用6 Hz的刺激和静态呈现来测量心理物理学对比度阈值。对比度敏感度计算为合并的视锥细胞对比度阈值的反函数。对于红-绿光栅，ssVECP和两种心理物理学对比度敏感度函数（CSF）均为低通函数。对于电生理学，在0.4 cpd时发现最高的对比度敏感度值（1.95±0.15）。ssVECP CSF与动态心理物理学CSF相似，而静态CSF在0.4至6 cpd范围内具有更高的值（方差分析，P<0.05）。蓝-黄颜色函数没有显示出特定的调谐形状；然而，在高空间频率下，诱发电位显示出比心理物理学方法更高的对比度敏感度（方差分析，P<0.05）。诱发电位可可靠地用于评估与心理物理学阈值一致的红-绿颜色CSF，主要是如果将相同的时间特性应用于刺激。对于蓝-黄CSF，在高空间频率下电生理学和心理物理学之间的相关性较差，这可能是由于色差对这种刺激的影响更大。
