【作者】 杨元；

【导师】 邱意弘；

【作者基本信息】 上海交通大学 ， 生物医学工程， 2010， 硕士

【摘要】 人工视觉假体研究已经证实基于光幻点模式的假体视觉可以恢复非先天性失明患者的一部分视觉功能(例如,物体识别和文字阅读)。在这些视觉功能中,面孔识别对人类是十分重要的,因为它在日常社交活动中发挥着举足轻重的作用。尽管行为学实验已经证实了假体视觉下面孔识别的有效性,但幻点面孔的早期处理机制仍然需要通过神经生理学研究来阐明。本论文旨在通过神经电生理实验和数学计算方法研究仿真假体视觉下面孔处理的早期机制。这不仅会为评价光幻点模式视觉假体的有效性提供一个客观的依据,也将有助于测试和改进假体视觉设计中使用到的图像处理策略。本文主要研究内容包括事件相关电位(ERP)成分分析和数学计算(ICA,溯源分析)两个部分:在第一部分,我们在ERP实验中使用面孔和物体的照片和它们对应的光幻点形式的图片作为刺激图,并在实验中记录了皮层脑电信号,然后通过叠加平均得到各类刺激对应的ERP。我们通过在枕颞叶区(TP7/8, P7/8, PO7/8和O1/2)测量并分析面孔敏感的ERP成分来探索假体视觉下面孔识别的早期机制。我们的结果表明(1)正常面孔和光幻点面孔都可以诱发显著的P1和N170;(2)光幻点面孔刺激诱发的N170较正常面孔刺激要小,但这一现象对P1而言是不显著的;(3)光幻点面孔刺激导致了P1和N170潜伏期的延迟。因此,我们认为:(1)早期面孔处理在光幻点模式下被诱发;(2)光幻点面孔在图像上的不连续性和高频段的信息丢失主要削弱了面孔处理的精细处理阶段而非粗略处理阶段;(3)光幻点刺激模式干扰了面孔处理的整个阶段,不仅干扰了精细处理阶段而且还包括了粗略处理阶段。在第二部分,我们通过对在第一部分中记录到的多通道脑电信号进行独立成分分析(ICA),寻找到了与面孔敏感的EEG独立成分,并用偶极子溯源分析算法和四层头部模型BESA 2000来对其进行溯源。最后,研究该独立成分对面孔敏感的ERP成分P1和N170的贡献,以及光幻点模式面孔对该独立的成分的影响。我们的研究发现:(1)独立成分IC-FS是面孔敏感的,其偶极子源位于梭状回(fusiform gyrus,FG)区域;(2)IC-FS是造成面孔刺激下大幅值P1和N170的主要独立成分,它与面孔的构形处理有关;(3)光幻点模式影响了面孔的构形处理,进而对面孔敏感独立成分(IC– FS)造成影响,最后导致P1的潜伏期和N170的潜伏期和幅值的改变。综上所述,本文阐明了光幻点(假体视觉)模式对面孔处理机制的影响,使得我们对假体视觉环境下面孔识别神经电生理机制有了一个更深入的了解。同时,这也将为测试现有视觉假体的有效性提供了一个新的手段,即通过测量神经电生理数据(EEG),分析面孔敏感ERP成分和独立成分的变化来评价假体视觉环境对面孔识别的影响。更多还原

【Abstract】 Artificial vision studies have validated that phosphene-based prosthetic vision could functionally recover some basic visual abilities (e.g., object perception and text reading) of non-congenitally blind individuals. Among these visual abilities, face perception is very important to humans due to its critical role in daily social interactions. Behavioral studies have tested and demonstrated the feasibility of face perception under phosphene-based prosthetic vision; however, neurophysiologic studies are required to elucidate the early visual processing mechanisms of phosphene faces.This thesis aimed to investigate the early face processing mechanism underlying the simulated prosthetic vision via electro-neurophysiologic and computational methods, which may not only provide an objective criterion for evaluating the efficacy of phosphene-based visual prostheses but also help test and improve the image processing strategies used in visual prosthesis design. The content of the thesis includes two main sections:In the first section, a face perception experiment was implemented using photographs of normal faces, non-face objects and their corresponding phosphene images. Electroencephalogram (EEG) was recorded with scalp electrodes during the experiment; and event-related potentials (ERPs) were derived by grand averaging the trials corresponding to each type of stimuli. We measured and analyzed face-sensitive ERP components at or near occipito-temporal areas (the ventral visual pathway), i.e., TP7/8, P7/8, PO7/8 and O1/2, to explore the early mechanism of face perception under prosthetic vision. Our results showed that (1) both normal and phosphene face stimuli could elicit prominent P1 and N170; (2) phosphene face stimuli caused significant amplitude suppression on N170 but not on P1 compared with normal stimuli; and (3) phosphene face stimuli also resulted in a significant delay on the latencies of both P1 and N170. Therefore, it was suggested that (1) early face processing was triggered in phosphene face perception; (2) the phosphene face pattern mainly impaired the fine processing stage rather than the coarse processing stage due to spatial discontinuity and information loss in high frequency; and (3) the phosphene pattern also disrupted the entire early processing of faces including both coarse and fine processing stages.In the second section, we employed independent component analysis (ICA) on the multi-channel EEGs that we recorded in the first section to seek for the independent face-sensitive EEG component. Then, we used source tracing algorithm and spherical four-shell BESA 2000 model to locate its source. Finally, we tested whether it contributed to face-sensitive ERP components P1 and N170 and whether it was modulated under phosphene faces. Our results showed that (1) an independent component IC-FS was found to be sensitive to face and the source of IC-FS located in fusiform gyrus; (2) IC-FS contributed to the face-sensitive P1 and N170 and related to face configural processing; (3) phosphene face pattern affected face configural processing so as the independent component IC-FS, leading to latency modulation on P1 and amplitude/latency modulation on N170.To sum up, this thesis systematically clarified how phosphene patterns affect the early face processing, offering a basic understanding of the neural representation of faces under phosphene vision. Meanwhile, it also provide a novel method for testing the efficacy of visual prosthesis, that is, evaluating the effect of prosthetic vision on face perception via recording electro-neurophysiologic data (EEG) and analysis the modulation of face sensitive ERPs and independent EEG components.更多还原