Logothetis N K, Pauls J
Division of Neuroscience, Baylor College of Medicine, Houston, Texas 77030, USA.
Cereb Cortex. 1995 May-Jun;5(3):270-88. doi: 10.1093/cercor/5.3.270.
A key question concerning the perception of 3D objects is the spatial reference frame used by the brain to represent them. The celerity of the recognition process could be explained by the visual system's ability to quickly transform stored models of familiar 3D objects, or by its ability to specify the relationship among viewpoint-invariant features or volumetric primitives that can be used to accomplish a structural description of an image. Alternatively, viewpoint-invariant recognition could be realized by a system endowed with the ability to perform an interpolation between a set of stored 2D templates, created for each experienced viewpoint. In the present study we set out to examine the nature of object representation in the primate in combined psychophysical-electrophysiological experiments. Monkeys were trained to recognize novel objects from a given viewpoint and subsequently were tested for their ability to generalize recognition for views generated by mathematically rotating the objects around any arbitrary axis. The perception of 3D novel objects was found to be a function of the object's retinal projection at the time of the recognition encounter. Recognition became increasingly difficult for the monkeys as the stimulus was rotated away from its familiar attitude. The generalization field for novel wire-like and spheroidal objects extended to about +/- 40 degrees around an experienced viewpoint. When the animals were trained with as few as three views of the object, 120 degrees apart, they could often interpolate recognition for all views resulting from rotations around the same axis. Recordings from inferotemporal cortex during the psychophysical testing showed a number of neurons with remarkable selectivity for individual views of those objects that the monkey had learned to recognize. Plotting the response of neurons as a function of rotation angle revealed systematic view-tuning curves for rotations in depth. A small percentage of the view-selective cells responded strongly for a particular view and its mirror-symmetrical view. For some of the tested objects, different neurons were found to be tuned to different views of the same object; the peaks of the view-tuning curves were 40-50 degrees apart. Neurons were also found that responded to the sight of unfamiliar objects or distractors. Such cells, however, gave nonspecific responses to a variety of other patterns presented while the monkey performed a simple fixation task.
一个与三维物体感知相关的关键问题是大脑用于表征它们的空间参照系。识别过程的快速性可以通过视觉系统快速转换熟悉的三维物体存储模型的能力来解释，或者通过其指定可用于完成图像结构描述的视点不变特征或体积基元之间关系的能力来解释。另外，视点不变识别可以由一个具备在为每个经历过的视点创建的一组存储二维模板之间进行插值能力的系统来实现。在本研究中，我们通过联合心理物理学 - 电生理学实验来探究灵长类动物中物体表征的本质。猴子经过训练，从给定视点识别新物体，随后测试它们对通过围绕任意轴数学旋转物体而生成的视图进行识别泛化的能力。发现对三维新物体的感知是识别相遇时物体视网膜投影的函数。随着刺激从其熟悉姿态旋转开，猴子的识别变得越来越困难。对于新的线状和球状物体，泛化场在经历过的视点周围扩展到约 +/- 40 度。当动物仅用相隔 120 度的三个物体视图进行训练时，它们通常能够对围绕同一轴旋转产生的所有视图进行插值识别。在心理物理学测试期间从颞下皮层进行的记录显示，许多神经元对猴子学会识别的那些物体的单个视图具有显著的选择性。将神经元的反应作为旋转角度的函数进行绘图，揭示了深度旋转的系统视图调谐曲线。一小部分视图选择性细胞对特定视图及其镜像对称视图有强烈反应。对于一些测试物体，发现不同的神经元被调谐到同一物体的不同视图；视图调谐曲线的峰值相隔 40 - 50 度。还发现神经元对不熟悉物体或干扰物的视觉有反应。然而，在猴子执行简单注视任务时，这类细胞对呈现的各种其他模式给出非特异性反应。
