Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Kapittelweg 29, 6525 EN Nijmegen, the Netherlands.
Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Kapittelweg 29, 6525 EN Nijmegen, the Netherlands.
Curr Biol. 2014 Jul 7;24(13):1531-5. doi: 10.1016/j.cub.2014.05.042.
An essential part of visual perception is the grouping of local elements (such as edges and lines) into coherent shapes. Previous studies have shown that this grouping process modulates neural activity in the primary visual cortex (V1) that is signaling the local elements [1-4]. However, the nature of this modulation is controversial. Some studies find that shape perception reduces neural activity in V1 [2, 5, 6], while others report increased V1 activity during shape perception [1, 3, 4, 7-10]. Neurocomputational theories that cast perception as a generative process [11-13] propose that feedback connections carry predictions (i.e., the generative model), while feedforward connections signal the mismatch between top-down predictions and bottom-up inputs. Within this framework, the effect of feedback on early visual cortex may be either enhancing or suppressive, depending on whether the feedback signal is met by congruent bottom-up input. Here, we tested this hypothesis by quantifying the spatial profile of neural activity in V1 during the perception of illusory shapes using population receptive field mapping. We find that shape perception concurrently increases neural activity in regions of V1 that have a receptive field on the shape but do not receive bottom-up input and suppresses activity in regions of V1 that receive bottom-up input that is predicted by the shape. These effects were not modulated by task requirements. Together, these findings suggest that shape perception changes lower-order sensory representations in a highly specific and automatic manner, in line with theories that cast perception in terms of hierarchical generative models.
视觉感知的一个重要组成部分是将局部元素（如边缘和线）组合成连贯的形状。先前的研究表明，这种分组过程会调节初级视觉皮层（V1）中信号局部元素的神经活动[1-4]。然而，这种调制的性质存在争议。一些研究发现形状感知会降低 V1 中的神经活动[2,5,6]，而另一些研究则报告在形状感知期间 V1 活动增加[1,3,4,7-10]。将感知视为生成过程的神经计算理论[11-13]提出，反馈连接携带预测（即生成模型），而前馈连接则表示自上而下的预测与自下而上的输入之间的不匹配。在这个框架内，反馈对早期视觉皮层的影响可能是增强或抑制，这取决于反馈信号是否与一致的自下而上的输入相匹配。在这里，我们通过使用群体感受野映射来量化在感知错觉形状时 V1 中的神经活动的空间分布，来检验这一假设。我们发现，形状感知会同时增加 V1 中具有形状感受野但未接收自下而上输入的区域的神经活动，并抑制接收形状预测的自下而上输入的 V1 区域的活动。这些影响不受任务要求的调节。这些发现表明，形状感知以高度特定和自动的方式改变了较低阶的感觉表示，与将感知视为分层生成模型的理论一致。
