Department of Psychology, University of Bologna, Viale Berti Pichat, 5, 40127, Bologna, Italy.
Institute for Experimental Psychology, University of Regensburg, 93053, Regensburg, Germany.
Sci Rep. 2023 Jul 31;13(1):12362. doi: 10.1038/s41598-023-39247-7.
The perception of coherent form configurations in natural scenes relies on the activity of early visual areas that respond to local orientation cues. Subsequently, high-level visual areas pool these local signals to construct a global representation of the initial visual input. However, it is still debated whether neurons in the early visual cortex respond also to global form features. Glass patterns (GPs) are visual stimuli employed to investigate local and global form processing and consist of randomly distributed dots pairs called dipoles arranged to form specific global configurations. In the current study, we used GPs and functional magnetic resonance imaging (fMRI) adaptation to reveal the visual areas that subserve the processing of oriented GPs. Specifically, we adapted participants to vertically oriented GP, then we presented test GPs having either the same or different orientations with respect to the adapting GP. We hypothesized that if local form features are processed exclusively by early visual areas and global form by higher-order visual areas, then the effect of visual adaptation should be more pronounced in higher tier visual areas as it requires global processing of the pattern. Contrary to this expectation, our results revealed that adaptation to GPs is robust in early visual areas (V1, V2, and V3), but not in higher tier visual areas (V3AB and V4v), suggesting that form cues in oriented GPs are primarily derived from local-processing mechanisms that originate in V1. Finally, adaptation to vertically oriented GPs causes a modification in the BOLD response within early visual areas, regardless of the relative orientations of the adapting and test stimuli, indicating a lack of orientation selectivity.
在自然场景中感知连贯的形式结构依赖于早期视觉区域的活动，这些区域对局部方向线索做出反应。随后，高级视觉区域整合这些局部信号，构建初始视觉输入的全局表示。然而，关于早期视觉皮层中的神经元是否也对全局形式特征做出反应，仍存在争议。玻璃图案（GP）是用于研究局部和全局形式处理的视觉刺激，由随机分布的点对组成，称为偶极子，排列成特定的全局配置。在当前的研究中，我们使用 GP 和功能磁共振成像（fMRI）适应来揭示处理定向 GP 的视觉区域。具体来说，我们让参与者适应垂直定向的 GP，然后呈现具有与适应 GP 相同或不同方向的测试 GP。我们假设，如果局部形式特征仅由早期视觉区域处理，而全局形式特征由更高阶视觉区域处理，那么视觉适应的效果在更高阶视觉区域中应该更明显，因为它需要对模式进行全局处理。与这一预期相反，我们的结果表明，GP 的适应在早期视觉区域（V1、V2 和 V3）中很稳健，但在更高阶视觉区域（V3AB 和 V4v）中不明显，这表明定向 GP 中的形式线索主要来自于起源于 V1 的局部处理机制。最后，无论适应和测试刺激的相对方向如何，垂直定向 GP 的适应都会导致早期视觉区域内 BOLD 反应的改变，这表明缺乏方向选择性。
