Van Humbeeck Nathalie, Putzeys Tom, Wagemans Johan
Laboratory of Experimental Psychology, Department of Brain & Cognition, University of Leuven, Leuven, Belgium.
PLoS Comput Biol. 2016 Oct 26;12(10):e1005155. doi: 10.1371/journal.pcbi.1005155. eCollection 2016 Oct.
Two stimuli alternately presented at different locations can evoke a percept of a stimulus continuously moving between the two locations. The neural mechanism underlying this apparent motion (AM) is thought to be increased activation of primary visual cortex (V1) neurons tuned to locations along the AM path, although evidence remains inconclusive. AM masking, which refers to the reduced detectability of stimuli along the AM path, has been taken as evidence for AM-related V1 activation. AM-induced neural responses are thought to interfere with responses to physical stimuli along the path and as such impair the perception of these stimuli. However, AM masking can also be explained by predictive coding models, predicting that responses to stimuli presented on the AM path are suppressed when they match the spatio-temporal prediction of a stimulus moving along the path. In the present study, we find that AM has a distinct effect on the detection of target gratings, limiting the maximum performance at high contrast levels. This masking is strongest when the target orientation is identical to the orientation of the inducers. We developed a V1-like population code model of early visual processing, based on a standard contrast normalization model. We find that AM-related activation in early visual cortex is too small to either cause masking or to be perceived as motion. Our model instead predicts strong suppression of early sensory responses during AM, consistent with the theoretical framework of predictive coding.
在不同位置交替呈现的两种刺激可以唤起一种在两个位置之间持续移动的刺激感知。这种表观运动(AM)背后的神经机制被认为是沿着AM路径调谐到各个位置的初级视觉皮层(V1)神经元的激活增加,尽管证据仍然不确凿。AM掩蔽是指沿着AM路径的刺激的可检测性降低,已被视为与AM相关的V1激活的证据。AM诱导的神经反应被认为会干扰对沿该路径的物理刺激的反应,从而损害对这些刺激的感知。然而,AM掩蔽也可以用预测编码模型来解释,该模型预测当沿着路径移动的刺激的时空预测与在AM路径上呈现的刺激相匹配时,对这些刺激的反应会受到抑制。在本研究中,我们发现AM对目标光栅的检测有显著影响,在高对比度水平下限制了最大性能。当目标方向与诱导物的方向相同时,这种掩蔽最强。我们基于标准对比度归一化模型开发了一种早期视觉处理的类似V1的群体编码模型。我们发现早期视觉皮层中与AM相关的激活太小,既不会导致掩蔽,也不会被感知为运动。相反,我们的模型预测在AM期间早期感觉反应会受到强烈抑制,这与预测编码的理论框架一致。