Nakayama K, Mackeben M
Vision Res. 1982;22(10):1261-71. doi: 10.1016/0042-6989(82)90138-9.
Macaque monkeys were trained to fixate a small spot while we recorded epidural steady state visual evoked potentials (SSVEP) in response to counterphase modulated sinusoidal gratings. This led to the following results: (1) the SSVEP can show either broad or narrow spatial frequency tuning, depending on electrode location, temporal frequency, contrast and method of analysis. (2) The SSVEP can also show narrow temporal frequency tuning, as narrow as 0.5 octave at half height. (3) Contrast functions relating VEP amplitude to log contrast were highly nonlinear. We propose that they are the composite of at least two distinct linear functions, one with a shallow slope for low contrasts and one with a significantly steeper slope for the higher contrasts. (4) Extrapolation of the low contrast function to zero voltage can lead to an excellent match with psychophysical functions. A similar extrapolation of the high contrast function, however, leads to a contrast value much higher than the psychophysical threshold. These findings suggest that the SSVEP can reflect the activity of two distinct neural mechanisms responsive to pattern stimulation. The degree to which either mechanism is evident determines the spatial and temporal frequency tuning of the VEP.
我们训练猕猴在注视一个小光点的同时，记录其硬膜外稳态视觉诱发电位（SSVEP）对反相调制正弦光栅的反应。结果如下：（1）根据电极位置、时间频率、对比度和分析方法，SSVEP可表现出宽或窄的空间频率调谐。（2）SSVEP也可表现出窄的时间频率调谐，半高宽可达0.5倍频程。（3）将VEP振幅与对数对比度相关的对比度函数具有高度非线性。我们认为它们是至少两个不同线性函数的组合，一个在低对比度时斜率较浅，另一个在高对比度时斜率明显更陡。（4）将低对比度函数外推到零电压可与心理物理学函数实现极佳匹配。然而，对高对比度函数进行类似外推会得到一个远高于心理物理学阈值的对比度值。这些发现表明，SSVEP可反映对模式刺激作出反应的两种不同神经机制的活动。任一机制的明显程度决定了VEP的空间和时间频率调谐。
