The detectability of contrast modulation (M) of sinusoidal gratings was explored at the rate of 8 Hz. The luminance profile of a contrast modulated sinusoidal grating is L = L(1 + C cos 2 pi F chi). This stimulus may also be regarded as the sum of a steady grating pattern and counter phase flicker of the same spatial frequency. 2. Contrast modulation sensitivity (1/M) was established in five observers at several levels of constract and over a range of spatial frequencies, where M = delta C/C of delta C is the just detectable contrast change and C is the mean contrast of the grating. The slope of a modulation sensitivity function (C/delta C vs. C) is 1 (i.e. delta C = constant) near threshold contrast at each spatial frequency, but in the suprathreshold contrast range the slope flattens from close to 1 at 1.5 c/deg to almost 0 (delta C/C = constant) at 12 c/deg. 3. Adaptation to a high contrast steady grating of the same spatial frequency as the contrast modulated test gratings shifts each modulation sensitivity function to the right at low contrasts, but not at high. As a result the adapted curves cross their corresponding unadapted ones. At each spatial frequency the modulation sensitivity function is now fitted by a straight line of slope 1. While delta C needs to be higher than half the detection threshold of the same grating at spatial frequencies above 3 c/deg, in the adapted condition the values are nearly equal at each frequency. Thus pattern adaptation unmasks the threshold of the counterphase component of the contrast modulated grating near threshold contrast as well as above it. The phase of the steady adapting grating, relative to the steady component of the test grating, does not make any difference. 4. Apparently contrast modulation reveals differences beyond threshold sensitivity between spatial frequencies adjacent to the peak of the contrast sensitivity curve. For each spatial frequency channel there must be different neural coupling between steady and modulated inputs. Electrophysiological studies using contrast modulated gratings would be useful in the exploration of individual and ensemble properties of neurones of the visual cortex.
摘要
以8赫兹的频率探究了正弦光栅对比度调制（M）的可检测性。对比度调制正弦光栅的亮度分布为L = L(1 + C cos 2πFχ)。该刺激也可视为具有相同空间频率的稳定光栅图案和反相闪烁的总和。2. 在五个观察者中，在几个对比度水平和一系列空间频率上确定了对比度调制灵敏度（1/M），其中M = ΔC/C，ΔC是刚刚可检测到的对比度变化，C是光栅的平均对比度。在每个空间频率的阈值对比度附近，调制灵敏度函数（C/ΔC对C）的斜率为1（即ΔC =常数），但在超阈值对比度范围内，斜率从1.5周/度时接近1逐渐变平，到12周/度时几乎为0（ΔC/C =常数）。3. 适应与对比度调制测试光栅具有相同空间频率的高对比度稳定光栅，会使每个调制灵敏度函数在低对比度时向右移动，但在高对比度时不会。结果，适应曲线与相应的未适应曲线相交。在每个空间频率上，调制灵敏度函数现在由斜率为1的直线拟合。虽然在高于3周/度的空间频率上，ΔC需要高于相同光栅检测阈值的一半，但在适应条件下，每个频率的值几乎相等。因此，图案适应在阈值对比度附近以及高于阈值对比度时，揭示了对比度调制光栅反相成分的阈值。稳定适应光栅相对于测试光栅稳定成分的相位没有任何影响。4. 显然，对比度调制揭示了在对比度灵敏度曲线峰值附近相邻空间频率之间超出阈值灵敏度的差异。对于每个空间频率通道，稳定输入和调制输入之间必须存在不同的神经耦合。使用对比度调制光栅的电生理研究将有助于探索视觉皮层神经元的个体和整体特性。
