School of Optometry and Vision Science, University of New South Wales, Sydney, Australia.
Invest Ophthalmol Vis Sci. 2012 Aug 15;53(9):5527-35. doi: 10.1167/iovs.11-9325.
We investigated the effects of image contrast, stimulus density, and viewing distance upon a multifocal steady-state visual evoked potential (MSV) method.
Fourteen adults with normal vision (mean age = 27.0 ± 6.6 years; 6 males) participated in the study. Each of the stimulus regions of the multifocal ensembles presented a contrast modulated grating, displaying spatial and temporal frequencies that evoke the spatial frequency doubling illusion. All subjects were tested at five contrasts: 0.06, 0.11, 0.22, 0.45, and 0.89; viewed at 16, 32, and 128 cm. A multivariate linear model estimated factors for each stimulus region, recording channel, number of stimuli (9 or 17 regions), and sex; and covariates for contrast, and octaves of viewing distance, and age.
The responses per unit area for the 17-region display were significantly larger than for the 9-region display (P < 10⁻¹²). The contrast-response function could be described by a power law with exponent 0.068 (P < 0.008). The effect of viewing distance was small but significant: response amplitude dropped by -0.17 ± 0.03 dB per octave of viewing distance (P < 10⁻⁶), or 10% over 8 octaves.
The response per unit area indicated that cortical folding diminishes responses to larger stimuli. Viewing distance did not greatly affect response amplitude. This suggested that we can use similar, but scaled, stimuli to study central and peripheral disease. The rapidly saturating contrast responses imply that there would be nothing lost from testing at contrasts as low as 20% given that higher, saturating contrasts might mask visual field defects.
我们研究了图像对比度、刺激密度和观察距离对多焦点稳态视觉诱发电位（MSVEP）方法的影响。
14 名视力正常的成年人（平均年龄=27.0±6.6 岁；6 名男性）参与了这项研究。多焦点集合的每个刺激区域呈现对比度调制光栅，显示出空间和时间频率，从而引起空间频率加倍错觉。所有受试者在五个对比度下进行测试：0.06、0.11、0.22、0.45 和 0.89；观察距离为 16、32 和 128cm。多元线性模型估计了每个刺激区域、记录通道、刺激数量（9 或 17 个区域）和性别因素；以及对比度、观察距离和年龄的倍频的协变量。
17 个区域显示的单位面积响应明显大于 9 个区域显示的响应（P<10⁻¹²）。对比度-响应函数可以用幂律来描述，指数为 0.068（P<0.008）。观察距离的影响虽然很小但很显著：响应幅度每增加一个八度就下降-0.17±0.03dB（P<10⁻⁶），8 个八度后下降 10%。
单位面积的响应表明，皮质折叠会降低对较大刺激的反应。观察距离对响应幅度的影响不大。这表明，我们可以使用类似但经过缩放的刺激来研究中枢和周围疾病。对比度快速饱和的响应意味着，在测试对比度低至 20%的情况下，不会有任何损失，因为更高的饱和对比度可能会掩盖视野缺陷。
