McLean J, Palmer L A
Department of Neuroscience, University of Pennsylvania, Philadelphia 19104.
Vis Neurosci. 1994 Mar-Apr;11(2):295-306. doi: 10.1017/s0952523800001644.
The amplitude spectra of simple cells in areas 17 and 18 were estimated in two and three dimensions (2-D and 3-D) using drifting sinusoidal gratings. In 2-D, responses were sampled with 16 x 16 resolution in spatial and temporal frequency at the optimal orientation. In 3-D, responses were sampled with 12 x 12 x 10 resolution in spatial frequency, orientation, and temporal frequency. For 45/50 cells studied, the spatial attributes of the receptive fields (RFs) were independent of temporal frequency except for a scale factor. The five exceptions to this general finding could be described as follows: For four area 17 cells, responses in the null direction increased with temporal frequency, reducing direction selectivity. For one area 18 cell, the optimal spatial frequency increased with temporal frequency and vice versa. The 2-D discrete Fourier transform was applied to all of the estimated amplitude spectra assuming zero spatial and temporal phase. These transforms were compared with the results of first-order reverse correlations as described in the previous paper (McLean et al., 1994). Direction selective cells exhibited excitatory subregions that were obliquely oriented in space-time in both the raw correlation data and inverse transforms of the spectral data. The slopes of the subregions found in these two measures were highly correlated. Direction indices obtained from space and frequency domain measures were comparable. We demonstrate that the spectral response profiles of most simple cells are aligned with the coordinate axes in frequency domain. That is, they may be considered one-quadrant separable, suggesting that these cells are not velocity tuned per se, but are tuned for spatiotemporal frequency. The spectral bandwidth establishes the range of velocities to which these cells will respond. These findings are consistent with the one-quadrant separability constraint of linear quadrature models. We conclude that most simple cells perform as roughly linear filters in two dimensions of space and time.
使用漂移正弦光栅在二维和三维（2-D和3-D）中估计了17区和18区简单细胞的振幅谱。在二维中，在最佳方向上以16×16的空间和时间频率分辨率对响应进行采样。在三维中，以12×12×10的空间频率、方向和时间频率分辨率对响应进行采样。对于所研究的45/50个细胞，除比例因子外，感受野（RF）的空间属性与时间频率无关。这一普遍发现的五个例外情况可描述如下：对于四个17区细胞，零方向的响应随时间频率增加，降低了方向选择性。对于一个18区细胞，最佳空间频率随时间频率增加，反之亦然。假设空间和时间相位为零，将二维离散傅里叶变换应用于所有估计的振幅谱。将这些变换与前一篇论文（McLean等人，1994年）中描述的一阶反向相关性结果进行了比较。方向选择性细胞在原始相关性数据和光谱数据的逆变换中均表现出在时空上倾斜定向的兴奋性子区域。在这两种测量中发现的子区域斜率高度相关。从空间和频域测量获得的方向指数具有可比性。我们证明，大多数简单细胞的光谱响应轮廓在频域中与坐标轴对齐。也就是说，它们可以被认为是一象限可分离的，这表明这些细胞本身不是速度调谐的，而是针对时空频率进行调谐的。光谱带宽确定了这些细胞将响应的速度范围。这些发现与线性正交模型的一象限可分离性约束一致。我们得出结论，大多数简单细胞在空间和时间的二维中大致表现为线性滤波器。
