Brain and Mind Institute, University of Western Ontario, London, Ontario, Canada; Neuroscience Program, University of Western Ontario, London, Ontario, Canada.
Brain and Mind Institute, University of Western Ontario, London, Ontario, Canada.
Neuropsychologia. 2021 Dec 10;163:108080. doi: 10.1016/j.neuropsychologia.2021.108080. Epub 2021 Oct 30.
Auditory short-term memory is often conceived of as a unitary capacity, with memory for different auditory materials (such as syllables, pitches, rhythms) posited to rely on similar neural mechanisms. One spontaneous behavior observed in short-term memory studies is 'chunking'. For example, individuals often recount digit sequences in groups, or chunks, of 3-4 digits, and chunking is associated with better performance. Chunking may also operate in musical rhythm, with beats acting as potential chunk boundaries for tones in rhythmic sequences. Similar to chunking, beat-based structure in rhythms also improves performance. Thus, it is possible that beat processing relies on the same mechanisms that underlie chunking of verbal material. The current fMRI study examined whether beat perception is indeed a type of chunking, measuring brain responses to chunked and 'unchunked' letter sequences relative to beat-based and non-beat-based rhythmic sequences. Participants completed a sequence discrimination task, and comparisons between stimulus encoding, maintenance, and discrimination were made for both rhythmic and verbal sequences. Overall, rhythm and verbal short-term memory networks overlapped substantially. When contrasting rhythmic and verbal conditions, rhythms activated basal ganglia, supplementary motor area, and anterior insula more than letter strings did, during both encoding and discrimination. Verbal letter strings activated bilateral auditory cortex more than rhythms did during encoding, and parietal cortex, precuneus, and middle frontal gyri more than rhythms did during discrimination. Importantly, there was a significant interaction in the basal ganglia during encoding: activation for beat-based rhythms was greater than for non-beat-based rhythms, but verbal chunked and unchunked conditions did not differ. The interaction indicates that beat perception is not simply a case of chunking, suggesting a dissociation between beat processing and chunking-based grouping mechanisms.
听觉短期记忆通常被认为是一种单一的能力，对不同听觉材料（如音节、音高、节奏）的记忆被认为依赖于相似的神经机制。在短期记忆研究中观察到的一种自发行为是“组块”。例如，个体经常以 3-4 位数字为一组，即组块，来复述数字序列，并且组块与更好的表现相关。在音乐节奏中，组块可能也会起作用，节拍可能充当节奏序列中音调的潜在组块边界。与组块类似，节奏中的基于节拍的结构也能提高表现。因此，节拍处理可能依赖于构成言语材料组块的相同机制。目前的 fMRI 研究探讨了节拍感知是否确实是一种组块，通过测量相对于基于节拍和非基于节拍的节奏序列，对组块和“非组块”字母序列的大脑反应。参与者完成了序列辨别任务，并对节奏和言语序列的刺激编码、保持和辨别进行了比较。总体而言，节奏和言语短期记忆网络有很大的重叠。当对比节奏和言语条件时，在编码和辨别过程中，与字母串相比，节奏更能激活基底神经节、辅助运动区和前岛叶。在编码过程中，与节奏相比，言语字母串更能激活双侧听觉皮层，而在辨别过程中，与节奏相比，顶叶皮层、楔前叶和中额回的激活更多。重要的是，在编码过程中基底神经节存在显著的交互作用：基于节拍的节奏的激活大于非基于节拍的节奏，但言语组块和非组块条件没有差异。这种相互作用表明节拍感知不仅仅是一种组块，这表明节拍处理与基于组块的分组机制之间存在分离。
