Multivariate patterns in object-selective cortex dissociate perceptual and physical shape similarity.
Multivariate patterns in object-selective cortex dissociate perceptual and physical shape similarity.
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DOI：
10.1371/journal.pbio.0060187
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发表时间：
2008-07-29
期刊：
影响因子：
9.8
通讯作者：
Kanwisher, Nancy
中科院分区：
文献类型：
--
作者：
Haushofer, Johannes;Livingstone, Margaret S.;Kanwisher, Nancy
先前的研究已经确定枕叶外侧复合体（lateral ocipital complex，简称CMPs）是人类表征物体形状的关键皮层区域。然而，很少有人知道的性质，所包含的表征，以及它们的关系，感性经验的形状。我们使用人类功能性MRI来测量成对的新形状之间的物理，行为和神经相似性，以询问是否包含在子区域中的形状表征更紧密地反映了物理刺激本身，或者这些刺激的感知体验。感知相似性措施，每对形状获得从心理物理相同不同的任务;物理相似性措施的刺激参数的基础上;和神经相似性措施，从多体素模式分析方法应用于前额叶（PFs）和后额叶（LO）。我们发现，模式的成对形状相似性LO最接近匹配的物理形状相似性，而形状相似性的pFs最接近匹配的感知形状相似性。此外，形状表征在LO中的参与者之间是相似的，但在PF中的参与者之间是高度可变的。总之，这些研究结果表明，激活模式的对象选择性皮层的子区域编码对象根据一个层次结构，与刺激为基础的表示在后部区域和主观和特定的代表在前部区域。早在公元1031年，阿拉伯学者伊本·海赛姆认为，视觉体验不是真实的，而是固有的主观性。在过去的几十年里，这一观察引起了视觉神经科学的核心问题之一：视觉刺激的主观体验如何与大脑中的神经表征相关？众所周知，视觉形状是在一个名为枕外侧复合体（lateral occipital complex，简称CAMPER）的大脑区域中表现出来的。然而，这些表征是否反映了物理或感知刺激的特征？我们向观察者提供了一组复杂的视觉刺激，并获得了这些刺激的三个相似性度量：基于刺激参数的物理相似性度量;基于辨别性能的行为相似性度量;最后基于多变量模式分析的神经相似性度量。我们发现，在前额叶，神经刺激的相似性与主观知觉的相似性，但不与物理刺激的相似性;相反的是真实的后额叶。此外，神经相似性是一致的参与者在后颅窝，但高度可变的参与者在前颅窝。总之，这些研究结果提出了一个两部分的答案，皮质对象的表征与主观经验的问题：前区似乎包含主观的，个别可变的形状表征，而后区包含刺激为基础的形状表征。视觉形状的主观体验如何与大脑中这些形状的神经表征相关？使用心理物理学，功能磁共振成像和多变量模式分析方法，这项研究表明，激活模式在前面，形状选择性的大脑区域反映感知形状的相似性，而模式在后方地区反映物理相似性。
Prior research has identified the lateral occipital complex (LOC) as a critical cortical region for the representation of object shape in humans. However, little is known about the nature of the representations contained in the LOC and their relationship to the perceptual experience of shape. We used human functional MRI to measure the physical, behavioral, and neural similarity between pairs of novel shapes to ask whether the representations of shape contained in subregions of the LOC more closely reflect the physical stimuli themselves, or the perceptual experience of those stimuli. Perceptual similarity measures for each pair of shapes were obtained from a psychophysical same-different task; physical similarity measures were based on stimulus parameters; and neural similarity measures were obtained from multivoxel pattern analysis methods applied to anterior LOC (pFs) and posterior LOC (LO). We found that the pattern of pairwise shape similarities in LO most closely matched physical shape similarities, whereas shape similarities in pFs most closely matched perceptual shape similarities. Further, shape representations were similar across participants in LO but highly variable across participants in pFs. Together, these findings indicate that activation patterns in subregions of object-selective cortex encode objects according to a hierarchy, with stimulus-based representations in posterior regions and subjective and observer-specific representations in anterior regions. As early as 1031 a.d., the Arab scholar Ibn al-Haytham suggested that visual experience was not veridical, but inherently subjective. During the last few decades, this observation has given rise to one of the core questions in visual neuroscience: how does the subjective experience of visual stimuli relate to their neural representations in the brain? It is well-known that visual shape is represented in a brain region called lateral occipital complex (LOC). However, do these representations reflect physical or perceptual stimulus characteristics? We presented observers with a set of complex visual stimuli and obtained three measures of similarity for these stimuli: a physical similarity measure based on stimulus parameters; a behavioral similarity measure based on discrimination performance; and finally a neural similarity measure based on multivariate pattern analyses in LOC. We found that in anterior LOC, neural stimulus similarities correlated with subjective perceptual similarities, but not with physical stimulus similarities; the reverse was true in posterior LOC. In addition, neural similarities were consistent across participants in posterior LOC, but highly variable across participants in anterior LOC. Together these findings suggest a two-part answer to the question of how cortical object representations relate to subjective experience: anterior regions appear to contain subjective, individually variable shape representations, whereas posterior regions contain stimulus-based shape representations. How does the subjective experience of visual shapes relate to the neural representations of these shapes in the brain? Using psychophysics, functional MRI, and multivariate pattern analysis methods, this study shows that activation patterns in anterior, shape-selective brain regions reflect perceptual shape similarities, whereas patterns in posterior regions reflect physical similarities.
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