Department of Cognitive Science and ARC Centre of Excellence in Cognition and Its Disorders and Perception in Action Research Centre, Macquarie University, Sydney, New South Wales 2109, Australia.
Medical Research Council, Cognition and Brain Sciences Unit, Cambridge CB2 7EF, UK.
Neuroimage. 2016 May 15;132:59-70. doi: 10.1016/j.neuroimage.2016.02.019. Epub 2016 Feb 16.
Perceptual similarity is a cognitive judgment that represents the end-stage of a complex cascade of hierarchical processing throughout visual cortex. Previous studies have shown a correspondence between the similarity of coarse-scale fMRI activation patterns and the perceived similarity of visual stimuli, suggesting that visual objects that appear similar also share similar underlying patterns of neural activation. Here we explore the temporal relationship between the human brain's time-varying representation of visual patterns and behavioral judgments of perceptual similarity. The visual stimuli were abstract patterns constructed from identical perceptual units (oriented Gabor patches) so that each pattern had a unique global form or perceptual 'Gestalt'. The visual stimuli were decodable from evoked neural activation patterns measured with magnetoencephalography (MEG), however, stimuli differed in the similarity of their neural representation as estimated by differences in decodability. Early after stimulus onset (from 50ms), a model based on retinotopic organization predicted the representational similarity of the visual stimuli. Following the peak correlation between the retinotopic model and neural data at 80ms, the neural representations quickly evolved so that retinotopy no longer provided a sufficient account of the brain's time-varying representation of the stimuli. Overall the strongest predictor of the brain's representation was a model based on human judgments of perceptual similarity, which reached the limits of the maximum correlation with the neural data defined by the 'noise ceiling'. Our results show that large-scale brain activation patterns contain a neural signature for the perceptual Gestalt of composite visual features, and demonstrate a strong correspondence between perception and complex patterns of brain activity.
感知相似性是一种认知判断，代表了视觉皮层中复杂分层处理过程的终末阶段。先前的研究表明，粗尺度 fMRI 激活模式的相似性与视觉刺激的感知相似性之间存在对应关系，这表明看起来相似的视觉对象也具有相似的潜在神经激活模式。在这里，我们探索了人类大脑对视觉模式的时变表示与感知相似性的行为判断之间的时间关系。视觉刺激是由相同的感知单元（定向 Gabor 补丁）构建的抽象模式，因此每个模式都具有独特的全局形式或感知“格式塔”。可以从脑磁图 (MEG) 测量的诱发神经激活模式中解码出这些视觉刺激，然而，由于解码的相似性不同，刺激在其神经表示方面存在差异。在刺激开始后不久（从 50ms 开始），基于视网膜组织的模型预测了视觉刺激的表示相似性。在 80ms 时视网膜模型和神经数据之间的相关性达到峰值后，神经表示迅速演变，以至于视网膜组织不再足以解释大脑对刺激的时变表示。总体而言，大脑表示的最强预测因子是基于人类感知相似性判断的模型，该模型达到了与神经数据的最大相关性（由“噪声上限”定义）的极限。我们的研究结果表明，大脑的大规模激活模式包含了对复合视觉特征的感知格式塔的神经特征，并证明了感知与大脑活动的复杂模式之间存在很强的对应关系。
