Klimova Michaela, Kwon MiYoung
Department of Psychology, Northeastern University, Boston, Massachusetts 02115
J Neurosci. 2025 May 21;45(21):e1649242025. doi: 10.1523/JNEUROSCI.1649-24.2025.
Mesopic (dim light) conditions are prevalent in everyday environments, yet most human vision research is conducted under idealized, photopic (bright) conditions. Electrophysiological studies suggest that under mesopic conditions, contrast-encoding retinal ganglion cell receptive fields expand their center width while diminishing surround inhibition. These retinal modifications enhance light capture by increasing the summation area but they limit spatial resolution. However, the impact of mesopic conditions on human cortical spatial integration mechanisms remains unclear. To address this, we investigate how mesopic conditions affect early visuocortical processing, specifically spatial summation and surround suppression. Across two experiments, we acquired fMRI BOLD responses from 11 normally sighted participants of both sexes under photopic and mesopic conditions in visual areas V1-V3. The first experiment estimated population receptive field (pRF) properties while the second experiment assessed cortical surround suppression. Photopic and mesopic psychophysical surround suppression, contrast sensitivity function (CSF), and visual acuity were also measured. At the cortical level, mesopic conditions were associated with smaller pRF sizes, while surround suppression remained robust. At the perceptual level, mesopic conditions led to reduced acuity, lower CSF, and weaker suppression, diverging from the observed cortical effects. Importantly, individual differences linked these findings: participants who exhibited greater mesopic reductions in visual acuity also showed larger decreases in early visuocortical surround suppression, underscoring its role in contrast coding and spatial resolution. Altogether, our fMRI findings contrast with retinal electrophysiology and suggest that early visual cortex may employ distinct, perhaps compensatory, mechanisms in response to reduced retinal input under mesopic conditions.
中间视觉（暗光）条件在日常环境中普遍存在，但大多数人类视觉研究是在理想化的明视觉（强光）条件下进行的。电生理研究表明，在中间视觉条件下，对比编码视网膜神经节细胞的感受野会扩大其中心宽度，同时减弱外周抑制。这些视网膜变化通过增加总和面积来增强光捕获，但会限制空间分辨率。然而，中间视觉条件对人类皮层空间整合机制的影响仍不清楚。为了解决这个问题，我们研究了中间视觉条件如何影响早期视觉皮层处理，特别是空间总和和外周抑制。在两个实验中，我们在明视觉和中间视觉条件下，从11名正常视力的男女参与者的视觉区域V1-V3获取了功能磁共振成像血氧水平依赖（BOLD）反应。第一个实验估计群体感受野（pRF）特性，而第二个实验评估皮层外周抑制。还测量了明视觉和中间视觉的心理物理学外周抑制、对比敏感度函数（CSF）和视敏度。在皮层水平上，中间视觉条件与较小的pRF大小相关，而外周抑制仍然很强。在感知水平上，中间视觉条件导致视敏度降低、CSF降低和抑制减弱，这与观察到的皮层效应不同。重要的是，个体差异将这些发现联系起来：在中间视觉条件下视敏度降低幅度更大的参与者，其早期视觉皮层外周抑制的降低幅度也更大，这突出了其在对比编码和空间分辨率中的作用。总之，我们的功能磁共振成像结果与视网膜电生理学结果形成对比，表明早期视觉皮层可能采用不同的、也许是补偿性的机制来应对中间视觉条件下视网膜输入的减少。
