认知与发展心理学研究室知识库

    时间知觉是一种易受情绪影响的主观知觉体验，但尚不知这种时间扭曲效应是否必须依赖于对情绪线索的外显觉知。本文以不可见的恐惧线索为研究对象，结合心理物理学、颅内事件相关电位以及功能性核磁共振等方法，考察其与时距知觉的关系，并探索背后的认知机制(研究一)和脑机制(研究二)。
    在研究一中，我们设计了两组正交的黑白光栅，并将负性电击刺激与其中一组朝向的光栅建立恐惧情绪的条件化联结。然后，使用红绿相位相反的一对彩色光栅，使它们以高于闪光融合(critical flicker fusion, CFF )阂限的频率交替闪烁以形成稳定、融合的知觉，从而使条件化(CS+)和非条件化(CS-)的朝向信息完全不可见。在时程比较任务中，不可见CS+的时间知觉显著长于CS-。当刺激的物理呈现时间从250ms增长至SOOms时，知觉上的时距延长效应量亦随之加倍。我们粗略地探索了该时距延长效应在时间上的消退特性，发现它在建立恐惧联结后的30分钟之内便快速消失。注意资源的不均衡分配不足以解释该效应，因为我们在控制实验中发现不可见的cs+和cs一之间没有相对的视觉注意优势。当解除闪光融合，转而对完全可见的cs+和cs一进行时距比较时，上述时距延长效应消失;与此相反，当把不包含恐惧信息，但视觉显著性却显著不同的两类纹理材料通过闪光融合范式掩蔽至无意识状态之后，原本在可见条件下出现的时距扭曲效应却消失了。如此这种根据视觉意识水平不同而不同，并在习得性恐惧和视觉显著性之间表现出双分离的计时现象说明，无意识恐惧所诱导的时距延长效应可能依赖于一套专有利于无意识线索影响时间知觉的特异化的计时机制。
在研究二中，我们探索无意识的习得性恐惧延长时间知觉的脑机制。首先，它不可能被局域性的视觉区的神经能量的增强所中介:相比于静止不闪烁的黄色圆盘，在知觉上完全匹配的中性的闪光融合刺激虽然诱发了显著更强的，局限于视觉区的神经活动，但却不影响时间知觉。其次，该效应与恐惧加工的核心脑区—杏仁核关系紧密。从六名癫痈病人志愿者的杏仁核记录的颅内脑电的数据表明，在计时过程中，不可见的cs+相比cs一在杏仁核激活了显著不同的差异化反应;与行为上的意识分离效应一致，当对可见的cs+和cs-计时的过程中，杏仁核局部场电位的差异化反应不再显著。最后，采用核磁共振扫描的方法，探索无意识恐惧诱导时距延长效应的神经通路。结果发现，在计时任务中，偏侧化地分布于右脑的杏仁核和参与计时任务的核心脑区一一脑岛、辅助运动区和额下回一一对不可见cs+的BOLD响应显著强于cs-;相关分析表明，上述脑区的BOLD增强效应越大，无意识恐惧在行为上诱导的时距延长效应越强;动态因果模型的分析表明，相比cs-，杏仁核向额下回以及向脑岛的前馈连接在cs+条件下增加得越多，行为上的时距延长效应越强;计时脑区向杏仁核的反馈调节与行为效应无显著相关。在控制条件下，当对可见的cs+和cs一进行计时的过程中，杏仁核以及计时脑区的活动不再具有显著差异。
    以上实验结果表明，无意识的习得性恐惧刺激可以显著延长时距知觉，它可能依赖于一套专有利于无意识信息发挥作用的，特异化的计时机制;在右侧半球中，杏仁核与脑岛和额下回的前馈连接，而非反馈连接，可能是该效应所依赖的神经通路。

  Time perception of visual events is intertwined with conscious and emotional experiences, yet it remains unknown whether such temporal distortion effect depends on explicit awareness of emotional cues. In this dissertation, we focused on invisible conditioned fear and combined psychophysics, intra-cranial electroencephalography recording (iEEG) and functional magnetic resonance imaging (fMRI) to unlock the cognitive and neural mechanisms through which the invisible conditioned fear may take effect in sub-second time perception.
    In study 1，conditioned fear was created by repetitively pairing aversive electrical shocks to one of two sets of luminance gratings with orthogonal orientations. Following the conditioning phase, counter-phase chromatic gratings with the conditioned (CS+) and nonconditioned (CS一)orientations were rendered invisible through flickering at a frequency above the critical flicker fusion (CFF) threshold. In a temporal duration discrimination task, the invisible CS+ flicker was perceived significantly longer than the invisible CS一flicker. Magnitude of this temporal dilation effect doubled when the physical duration of stimulus presented increased from 250ms to SOOms. We roughly explored the extinguishing time course of this effect and found it fading swiftly to nonsignificant within 30 minutes. Asymmetric allocation of attentional sources may not explain the effect, since a control experiment found no difference between the invisible CS+ and CS一flickers in attentional capture. When only one part of the CS+ and CS-flickers were presented and thus all visual features of the gratings to be timed were explicitly visible, however, the temporal dilation effect disappeared.  Oppositely, another kind of temporal dilation effect induced by increase of visual saliency of neutral textures was observed in the visible condition only, it disappeared completely when these neutral textures were flickering above CFF threshold and thus rendered invisible.This double dissociation, dependent on visual awareness between conditioned fear and neutral visual saliency, suggests a specific timing mechanism adapted for conditioned fear outside the scope of visual awareness.
    In study 2，we studied the neural mechanisms underlying the temporal dilation effect induced by invisible conditioned fear. At first, it cannot be mediated by locally enhanced neural energy in the visual areas: chromatic flickers, though evokes larger neural energy selectively in the visual cortex, failed to dilate time perception relative to the static presentation of its perceptual counterpart. Secondly, this effect was closely related to the amygdala, a hub region for fear processing in the human brain. Intracranial electroencephalography (iEEG) data, recorded from electrodes implanted precisely in the human amygdala of six volunteer epilepsy patients, revealed that,during the temporal duration discrimination task, invisible CS+ flicker evoked local field potential significantly larger than that of the CS一In line with the behavioral findings, when the CS+ and CS一gratings to be timed were explicitly visible, no differential responses were observed in amygdala in vivo. At last, by using functional magnetic resonance imaging (fMRI), we explored in the whole brain what additional regions, together with amygdala, may account for the temporal dilation effect. During a revised oddball timing task, BOLD responses lateralized in the right hemisphere in the amygdala and core regions involved in timing, namely the insula, supplementary motor area (SMA) and inferior frontal gyrus (IFG), were significantly larger for invisible CS+ flicker than that for CS一flicker. These effects of significant BOLD enhancement were selectively tied to the invisible condition, which were nonsignificant while the visible CS+ and CS一were to be timed. Inter-individual correlation analysis revealed that larger BOLD enhancement in these four regions predicted more temporal dilation effect induced by invisible conditioned fear. Dynamic causal modeling analyses revealed that stronger feedforward modulation from the right amygdala to the IFG and Insula, induced by invisible CS+ relative to CS一，was associated with larger temporal dilation effect. These associations were not significant for the connectivity modulation backwards to the amygdala.
    Taken together, invisible conditioned fear may significantly dilate perceived temporal duration. This effect may depend on a timing mechanism specifically adapted for conditioned fear outside the scope of visual awareness. More specifically,feedforward rather than feedback connectivity from the amygdala to the insula and IFG in the right hemisphere may mediate the temporal dilation effect induced by invisible conditioned fear.