Burton Eliza, Wattam-Bell John, Rubin Gary S, Atkinson Janette, Braddick Oliver, Nardini Marko
Institute of Ophthalmology, University College London, London, UK.
Division of Psychology and Language Sciences, University College London, London, UK.
Vision Res. 2016 Apr;121:39-49. doi: 10.1016/j.visres.2016.01.008. Epub 2016 Feb 18.
Advances in potential treatments for rod and cone dystrophies have increased the need to understand the contributions of rods and cones to higher-level cortical vision. We measured form, motion and biological motion coherence thresholds and EEG steady-state visual evoked potentials (SSVEP) responses under light conditions ranging from photopic to scotopic. Low light increased thresholds for all three kinds of stimuli; however, global form thresholds were relatively more impaired than those for global motion or biological motion. SSVEP responses to coherent global form and motion were reduced in low light, and motion responses showed a shift in topography from the midline to more lateral locations. Contrast sensitivity measures confirmed that basic visual processing was also affected by low light. However, comparison with contrast sensitivity function (CSF) reductions achieved by optical blur indicated that these were insufficient to explain the pattern of results, although the temporal properties of the rod system may also play a role. Overall, mid-level processing in extra-striate areas is differentially affected by light level, in ways that cannot be explained in terms of low-level spatiotemporal sensitivity. A topographical shift in scotopic motion SSVEP responses may reflect either changes to inhibitory feedback mechanisms between V1 and extra-striate regions or a reduction of input to the visual cortex. These results provide insight into how higher-level cortical vision is normally organised in absence of cone input, and provide a basis for comparison with patients with cone dystrophies, before and after treatments aiming to restore cone function.
视杆和视锥营养不良潜在治疗方法的进展增加了理解视杆和视锥对高级皮层视觉贡献的必要性。我们在从明视觉到暗视觉的光照条件下，测量了形状、运动和生物运动连贯性阈值以及脑电图稳态视觉诱发电位（SSVEP）反应。低光照增加了所有三种刺激的阈值；然而，整体形状阈值比整体运动或生物运动阈值受到的损害相对更大。在低光照条件下，对连贯整体形状和运动的SSVEP反应降低，并且运动反应在地形图上显示出从中央线向更外侧位置的偏移。对比敏感度测量证实基本视觉处理也受到低光照的影响。然而，与通过光学模糊实现的对比敏感度函数（CSF）降低进行比较表明，这些不足以解释结果模式，尽管视杆系统的时间特性可能也起作用。总体而言，纹外区域的中级处理受光照水平的影响不同，其方式无法用低级时空敏感度来解释。暗视觉运动SSVEP反应的地形图偏移可能反映了V1和纹外区域之间抑制性反馈机制的变化，或者是视觉皮层输入的减少。这些结果为在没有视锥输入的情况下高级皮层视觉通常如何组织提供了见解，并为与视锥营养不良患者在旨在恢复视锥功能的治疗前后进行比较提供了基础。
