Hou Yuchen, Nanduri Devyani, Granley Jacob, Weiland James D, Beyeler Michael
Department of Computer Science, University of California, Santa Barbara, CA.
Department of Psychological & Brain Sciences, University of California, Santa Barbara, CA.
medRxiv. 2023 Dec 26:2023.07.21.23292908. doi: 10.1101/2023.07.21.23292908.
Retinal implants use electrical stimulation to elicit perceived flashes of light ("phosphenes"). Single-electrode phosphene shape has been shown to vary systematically with stimulus parameters and the retinal location of the stimulating electrode, due to incidental activation of passing nerve fiber bundles. However, this knowledge has yet to be extended to paired-electrode stimulation.
We retrospectively analyzed 3548 phosphene drawings made by three blind participants implanted with an Argus II Retinal Prosthesis. Phosphene shape (characterized by area, perimeter, major and minor axis length) and number of perceived phosphenes were averaged across trials and correlated with the corresponding single-electrode parameters. In addition, the number of phosphenes was correlated with stimulus amplitude and neuroanatomical parameters: electrode-retina and electrode-fovea distance as well as the electrode-electrode distance to ("between-axon") and along axon bundles ("along-axon"). Statistical analyses were conducted using linear regression and partial correlation analysis.
Simple regression revealed that each paired-electrode shape descriptor could be predicted by the sum of the two corresponding single-electrode shape descriptors ( < .001). Multiple regression revealed that paired-electrode phosphene shape was primarily predicted by stimulus amplitude and electrode-fovea distance ( < .05). Interestingly, the number of elicited phosphenes tended to increase with between-axon distance ( < .05), but not with along-axon distance, in two out of three participants.
The shape of phosphenes elicited by paired-electrode stimulation was well predicted by the shape of their corresponding single-electrode phosphenes, suggesting that two-point perception can be expressed as the linear summation of single-point perception. The notable impact of the between-axon distance on the perceived number of phosphenes provides further evidence in support of the axon map model for epiretinal stimulation. These findings contribute to the growing literature on phosphene perception and have important implications for the design of future retinal prostheses.
视网膜植入物利用电刺激引发可感知的闪光（“光幻视”）。由于刺激电极周围神经纤维束的偶然激活，单电极光幻视的形状已被证明会随刺激参数和刺激电极在视网膜上的位置而系统变化。然而，这一知识尚未扩展到双电极刺激。
我们回顾性分析了三名植入阿格斯II视网膜假体的盲人参与者绘制的3548张光幻视图。光幻视形状（以面积、周长、长轴和短轴长度为特征）和感知到的光幻视数量在各试验中进行平均，并与相应的单电极参数相关联。此外，光幻视数量还与刺激幅度和神经解剖学参数相关：电极与视网膜的距离、电极与中央凹的距离以及电极与电极之间沿轴突束的距离（“轴突间”）和沿轴突束的距离（“沿轴突”）。使用线性回归和偏相关分析进行统计分析。
简单回归显示，每个双电极形状描述符都可以通过两个相应单电极形状描述符的总和来预测（<0.001）。多元回归显示，双电极光幻视形状主要由刺激幅度和电极与中央凹的距离预测（<0.05）。有趣的是，在三名参与者中的两名中，诱发的光幻视数量倾向于随着轴突间距离增加（<0.05），但不随沿轴突距离增加。
双电极刺激引发的光幻视形状可以很好地由其相应单电极光幻视的形状预测，这表明两点感知可以表示为单点感知的线性总和。轴突间距离对感知到的光幻视数量的显著影响为视网膜外刺激的轴突图谱模型提供了进一步的证据支持。这些发现有助于丰富关于光幻视感知的文献，并对未来视网膜假体的设计具有重要意义。
