Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Germany.
Neuroimage. 2012 Nov 15;63(3):1730-42. doi: 10.1016/j.neuroimage.2012.08.017. Epub 2012 Aug 11.
Neuroimaging research has identified several brain systems sensitive to statistical regularities within environmental input. However, the continuous input impinging on sensory organs is rarely stationary and its degree of regularity may itself change over time. The goals of the current fMRI study were to identify systems sensitive to changes in statistical regularities within an ongoing stimulus, and determine to what extent sensitivity to such changes depends on intentional monitoring of order. We predicted that changes in regularity would be coded for in systems previously associated with statistical coding (hippocampus and middle frontal regions) or event segmentation (posterior medial regions). Participants listened to a rapid train of four different tones whose order levels fluctuated over time. In an active task, participants monitored the tones and indicated when they perceived a change in regularity; in a passive task, they performed a concurrent visuo-motor task and could ignore the auditory input. Behavioral responses in the active task were used to define points of consensus between participants regarding changes in regularity. Activity in 7.5s epochs that preceded these order-change points was contrasted with activity during matched-length epochs where no participant indicated a change in order. We found that brain regions differentiating these two types of epochs matched those identified in prior research as mediating event segmentation in narratives and movies. These consisted mainly of medial posterior parietal and occipital regions, with limited involvement of temporal and lateral frontal cortices and no hippocampal involvement. In both tasks, order-change epochs were associated with a higher BOLD response than stable-order epochs, but the specific regions showing this pattern varied across tasks. We suggest that partitioning an input stream on the basis of statistical shifts constitutes a basic neural function underlying the ability to segment both semantic and non-semantic inputs. We further discuss the implications of these findings for neurobiological theories of statistical coding and event segmentation.
神经影像学研究已经确定了几个对环境输入中统计规律敏感的大脑系统。然而，连续不断地冲击感官器官的输入很少是静止的，其规则性的程度本身可能会随时间变化。本 fMRI 研究的目的是确定对正在进行的刺激中统计规律变化敏感的系统，并确定对这些变化的敏感性在多大程度上依赖于对顺序的有意监测。我们预测，在以前与统计编码（海马体和中额叶区域）或事件分割（后内侧区域）相关的系统中，会对规则的变化进行编码。参与者听了一组快速的四个不同音调的音轨，其顺序水平随时间波动。在主动任务中，参与者监测音调并指出何时感知到规则的变化；在被动任务中，他们执行同时的视动任务并可以忽略听觉输入。在主动任务中的行为反应用于定义参与者对规则变化的共识点。在这些顺序变化点之前的 7.5 秒时段中的活动与在没有参与者表示顺序变化的匹配长度时段中的活动进行了对比。我们发现，区分这两种类型的时段的大脑区域与先前研究中确定的在叙事和电影中介导事件分割的区域相匹配。这些区域主要包括内侧后顶叶和枕叶区域，颞叶和外侧额叶皮质的参与有限，没有海马体的参与。在两种任务中，与稳定顺序的时段相比，顺序变化的时段与更高的 BOLD 反应相关，但表现出这种模式的特定区域在任务之间有所不同。我们认为，基于统计变化对输入流进行分区构成了分割语义和非语义输入的基本神经功能。我们进一步讨论了这些发现对统计编码和事件分割的神经生物学理论的意义。
