Rotational uncertainty refers to the fact that the reaction time (RT) for identifying an upright stimulus is longer when the target stimulus is presented in a sequence of stimuli with different orientations (SU condition) than upright stimuli only (AU condition). Up until now, the rotational uncertainty effect has been only revealed by behavior measures, and its underlying neural mechanism remains unclear. In this study, using the hand mental rotation paradigm and EEG recordings, we aimed to find the electrophysiological evidences of the rotational uncertainty from event-related potential (ERP) and event-related (de)synchronization (ERS/ERD) measurements. Compared with the upright hand stimuli in AU condition, the same stimuli in SU condition took longer RT, elicited stronger α-ERD and β-ERD, and evoked larger P100, P300 and the slow wave (SW) from -500 ms to -200 ms before response. In particular, the amplitude of SW difference (i.e., SW_SU-SW_AU) was negatively correlated with the extent of rotational uncertainty effect (i.e., RT_SU-RT_AU), with its source localized mainly in the right precentral and postcentral gyri, precuneus, and the left inferior parietal lobule. Our results suggested that identifying the upright hand stimuli in SU condition induced more activation of motor networks, and the rotational uncertainty influenced multiple cognitive processes from the early visual processing to late mental rotation and judging phases. The results implied that in SU condition, subjects might maintain readiness for the next possible mental rotation immediately after the last response, with more attention to the coming visual stimuli. Even for the upright stimuli, they might still prepare for the mental rotation, and even mentally rotate the stimuli in a minor angle.

旋转不确定性是指这样的事实，即当目标刺激以不同方向的刺激序列（SU条件）呈现时，识别竖立刺激的反应时间（RT）比仅竖立刺激（AU条件）更长。到目前为止，旋转不确定性效应仅通过行为手段得以揭示，其潜在的神经机制尚不清楚。在这项研究中，我们使用手部心理旋转范例和EEG记录，旨在从事件相关电位（ERP）和事件相关（去同步）（ERS / ERD）测量中找到旋转不确定性的电生理证据。与AU状态下的直立手刺激相比，SU状态下的相同刺激需要更长的RT，诱发更强的α-ERD和β-ERD，并诱发更大的P100，P300和慢波（SW）从-500毫秒到-200毫秒才响应。特别是，SW差异的幅度（即SW_SU -SW _AU）与旋转不确定性影响的程度呈负相关（即RT _SU -RT _AU）），其来源主要集中在右中央前和中央后回，前丘脑和左下顶叶。我们的研究结果表明，在SU状态下识别直立的手部刺激会诱导更多的运动网络激活，而旋转不确定性会影响从早期视觉处理到后期精神旋转和判断阶段的多个认知过程。结果表明，在SU状态下，受试者可能在上次反应后立即保持对下一次可能的心理旋转的准备，并更多地关注即将到来的视觉刺激。即使对于直立的刺激，他们仍可能为精神旋转做好准备，甚至在心理上以较小的角度旋转刺激。