Carlson Thomas A
Perception in Action Research Centre and Department of Cognitive Science and Centre for Cognition and its Disorders, Macquarie University, Sydney, NSW 2109, Australia
J Neurosci. 2014 Jun 11;34(24):8373-83. doi: 10.1523/JNEUROSCI.0548-14.2014.
The development of multivariate pattern analysis or brain "decoding" methods has substantially altered the field of fMRI research. Although these methods are highly sensitive to whether or not decodable information exists, the information they discover and make use of for decoding is often concealed within complex patterns of activation. This opacity of interpretation is embodied in influential studies showing that the orientation of visual gratings can be decoded from brain activity in human visual cortex with fMRI. Although these studies provided a compelling demonstration of the power of these methods, their findings were somewhat mysterious as the scanning resolution was insufficient to resolve orientation columns, i.e., orientation information should not have been accessible. Two theories have been put forth to account for this result, the hyperacuity account and the biased map account, both of which assume that small biases in fMRI voxels are the source of decodable information. In the present study, we use Hubel and Wiesel's (1972) classic ice-cube model of visual cortex to show that the orientation of gratings can be decoded from an unbiased representation. In our analysis, we identify patterns of activity elicited by the edges of the stimulus as the source of the decodable information. Furthermore, these activation patterns masquerade as a radial bias, a key element of the biased map account. This classic model thus sheds new light on the mystery behind orientation decoding by unveiling a new source of decodable information.
多变量模式分析或大脑“解码”方法的发展极大地改变了功能磁共振成像（fMRI）研究领域。尽管这些方法对是否存在可解码信息高度敏感，但它们发现并用于解码的信息通常隐藏在复杂的激活模式中。这种解释的不透明性体现在一些有影响力的研究中，这些研究表明，通过功能磁共振成像可以从人类视觉皮层的大脑活动中解码视觉光栅的方向。尽管这些研究有力地证明了这些方法的强大功能，但由于扫描分辨率不足以分辨方向柱，即方向信息本不应被获取，其研究结果多少有些神秘。针对这一结果提出了两种理论，即超敏锐度理论和偏差图谱理论，这两种理论都假定功能磁共振成像体素中的小偏差是可解码信息的来源。在本研究中，我们使用休伯尔和威塞尔（1972年）经典的视觉皮层冰块模型来表明，光栅的方向可以从无偏差表示中解码出来。在我们的分析中，我们将由刺激边缘引发的活动模式确定为可解码信息的来源。此外，这些激活模式伪装成一种径向偏差，这是偏差图谱理论的一个关键要素。因此，这个经典模型通过揭示可解码信息的新来源，为方向解码背后的谜团带来了新的启示。
