单侧空间忽略的右脑受损患者无法探索左侧空间。最近的脑电图和临床证据表明,忽视患者可能存在预测编码缺陷,即识别和利用环境中感官刺激之间的概率关联。为了获得对这个问题的直接见解,我们专注于预测编码的分层组件。我们记录了中枢诱发的脑电图反应,在四个中央音调序列的末尾呈现的左侧或右侧音调。左侧和右侧偏差音调会产生预先注意的失配否定性,反映了序列末尾音调的\'Local\'偏差的低阶预测误差。在声学环境中这些偏差的频率的高阶预测误差,即\'全球\'偏差,由P3响应标记。我们表明,当忽视患者沉浸在以频繁的左侧偏差音调为特征的声学环境中时,对于左侧偏差的音调和最后一个音调的不频繁遗漏,它们都没有表现出注意前的不匹配否定,而他们对不频繁的右侧偏差音调有不匹配的否定性。在同样的条件下,忽视患者对偏差音调的“全球”预测错误没有P300反应,包括那些不被忽视的右侧,和遗漏。与此相反,当右侧异常音调在声学环境中占主导地位时,忽视患者对右侧偏差音调和不频繁遗漏都有注意前失配否定,而对于不频繁的左侧偏差音调,它们没有显示不匹配的否定性。最重要的是,在相同的情况下,忽视患者对罕见的左侧异常音调的P300反应增强,尽管这些音调没有引起预先注意的不匹配否定。后一个发现表明,\'全局\'预测与不匹配否定提供的\'本地\'错误信号无关。这些结果证明了空间忽视综合征中预测编码的缺陷,并表明忽视患者的预测行为仅基于与空间右侧感觉事件频繁发生有关的统计规律。
Right brain-damaged patients with unilateral spatial neglect fail to explore the left side of space. Recent EEG and clinical evidence suggests that neglect patients might suffer deficits in predictive coding, i.e. in identifying and exploiting probabilistic associations among sensory stimuli in the environment. To gain direct insights on this issue, we focussed on the hierarchical components of predictive coding. We recorded EEG responses evoked by central, left-side or right-side tones that were presented at the end of sequences of four central tones. Left-side and right-side deviant tones produce a pre-attentive Mismatch Negativity that reflects a lower-order prediction error for the \'Local\' deviation of the tone at the end of the sequence. Higher-order prediction errors for the frequency of these deviations in the acoustic environment, i.e. \'Global\' deviation, are marked by the P3 response. We show that when neglect patients are immersed in an acoustic environment characterized by frequent left-side deviant tones, they display no pre-attentive Mismatch Negativity both for left-side deviant tones and infrequent omissions of the last tone, while they have Mismatch Negativity for infrequent right-side deviant tones. In the same condition, neglect patients show no P300 response to \'Global\' prediction errors for deviant tones, including those in the non-neglected right-side, and omissions. In contrast to this, when right-side deviant tones are predominant in the acoustic environment, neglect patients have pre-attentive Mismatch Negativity both for right-side deviant tones and infrequent omissions, while they display no Mismatch Negativity for infrequent left-side deviant tones. Most importantly, in the same condition neglect patients show enhanced P300 response to infrequent left-side deviant tones, notwithstanding that these tones evoked no pre-attentive Mismatch Negativity. This latter finding indicates that \'Global\' predictions are independent of \'Local\' error signals provided by the Mismatch Negativity. These results qualify deficits of predictive coding in the spatial neglect syndrome and show that neglect patients base their predictive behaviour only on statistical regularities that are related to the frequent occurrence of sensory events on the right side of space.