Klímová Michaela, Bloem Ilona M, Ling Sam
Department of Psychological and Brain Sciences, Boston University, Boston, Massachusetts, United States.
Center for Systems Neuroscience, Boston University, Boston, Massachusetts, United States.
J Neurophysiol. 2025 Feb 1;133(2):539-546. doi: 10.1152/jn.00224.2024. Epub 2025 Jan 7.
Visuocortical responses are regulated by gain control mechanisms, giving rise to fundamental neural and perceptual phenomena such as surround suppression. Suppression strength, determined by the composition and relative properties of stimuli, controls the strength of neural responses in early visual cortex, and in turn, the subjective salience of the visual stimulus. Notably, suppression strength is modulated by feature similarity; for instance, responses to a center-surround stimulus in which the components are collinear to each other are weaker than when they are orthogonal. However, this feature-tuned aspect of normalization, and how it may affect the gain of responses, has been understudied. Here, we examine the contribution of the tuned component of suppression to contrast response modulations across the visual field. To do so, we used functional magnetic resonance imaging (fMRI) to measure contrast response functions (CRFs) in early visual cortex (areas V1-V3) in 10 observers while they viewed full-field center-surround gratings. The center stimulus varied in contrast between 2.67% and 96% and was surrounded by a collinear or orthogonal surround at full contrast. We found substantially stronger suppression of responses when the surround was parallel to the center, manifesting as shifts in the population CRF. The magnitude of the CRF shift was strongly dependent on voxel spatial preference and seen primarily in voxels whose receptive field spatial preference corresponds to the area straddling the center-surround boundary in our display, with little-to-no modulation elsewhere. Visuocortical responses are underpinned by gain control mechanisms. In surround suppression, it has been shown that suppression strength is affected by the orientation similarity between the center and surround stimuli. In this study, we examine the impact of orientation-tuned suppression on population contrast responses in early visual cortex and its spread across the visual field. Results show stronger suppression in parallel stimulus configurations, with suppression largely isolated to voxels near the center-surround boundary.
视皮层反应受增益控制机制调节，从而产生诸如周边抑制等基本的神经和感知现象。抑制强度由刺激的组成和相对属性决定，它控制着早期视觉皮层中神经反应的强度，进而控制视觉刺激的主观显著性。值得注意的是，抑制强度受特征相似性的调节；例如，对中心-周边刺激的反应，当各组成部分相互共线时比相互正交时更弱。然而，这种归一化的特征调谐方面以及它如何影响反应增益，一直未得到充分研究。在这里，我们研究抑制的调谐成分对整个视野中对比度反应调制的贡献。为此，我们使用功能磁共振成像（fMRI）来测量10名观察者在观看全场中心-周边光栅时早期视觉皮层（V1-V3区）的对比度反应函数（CRF）。中心刺激的对比度在2.67%至96%之间变化，并被全对比度的共线或正交周边所环绕。我们发现当周边与中心平行时，反应的抑制作用明显更强，表现为群体CRF的偏移。CRF偏移的幅度强烈依赖于体素的空间偏好，并且主要出现在其感受野空间偏好与我们显示中跨越中心-周边边界的区域相对应的体素中，其他地方几乎没有调制。视皮层反应由增益控制机制支撑。在周边抑制中，已经表明抑制强度受中心和周边刺激之间的方向相似性影响。在本研究中，我们研究方向调谐抑制对早期视觉皮层群体对比度反应的影响及其在整个视野中的传播。结果表明，在平行刺激配置中抑制作用更强，且抑制作用主要局限于靠近中心-周边边界的体素。
