Troyer Todd W, Brainard Michael S, Bouchard Kristofer E
Department of Biology and Neurosciences Institute, University of Texas at San Antonio, San Antonio, Texas;
Department of Physiology, University of California, San Francisco, California.
J Neurophysiol. 2017 Sep 1;118(3):1556-1566. doi: 10.1152/jn.00296.2017. Epub 2017 Jun 21.
To investigate mechanisms of action sequencing, we examined the relationship between timing and sequencing of syllables in Bengalese finch song. An individual's song comprises acoustically distinct syllables organized into probabilistic sequences: a given syllable potentially can transition to several different syllables (divergence points), and several different syllables can transition to a given syllable (convergence points). In agreement with previous studies, we found that more probable transitions at divergence points occur with shorter intersyllable gaps. One intuition for this relationship is that selection between syllables reflects a competitive branching process, in which stronger links to one syllable lead to both higher probabilities and shorter latencies for transitions to that syllable vs. competing alternatives. However, we found that simulations of competitive race models result in overlapping winning-time distributions for competing outcomes and fail to replicate the strong negative correlation between probability and gap duration found in song data. Further investigation of song structure revealed strong positive correlation between gap durations for transitions that share a common convergent point. Such transitions are not related by a common competitive process, but instead reflect a common terminal syllable. In contrast to gap durations, transition probabilities were not correlated at convergence points. Together, our data suggest that syllable selection happens early during the gap, with gap timing determined chiefly by the latency to syllable initiation. This may result from a process in which probabilistic sequencing is first stabilized, followed by a shortening of the latency to syllables that are sung more often. Bengalese finch songs consist of probabilistic sequences of syllables. Previous studies revealed a strong negative correlation between transition probability and the duration of intersyllable gaps. We show here that the negative correlation is inconsistent with previous suggestions that timing at syllable transitions is governed by a race between competing alternatives. Rather, the data suggest that syllable selection happens early during the gap, with gap timing determined chiefly by the latency to syllable initiation.
为了研究动作序列的机制，我们考察了 Bengalese 雀类歌声中音节的时间安排与序列之间的关系。个体的歌声由组织成概率序列的声学上不同的音节组成：给定的一个音节可能会过渡到几个不同的音节（发散点），并且几个不同的音节可以过渡到给定的一个音节（汇聚点）。与之前的研究一致，我们发现发散点处更可能的过渡发生在较短的音节间间隔时。对于这种关系的一种直觉是，音节之间的选择反映了一个竞争性分支过程，在这个过程中，与一个音节的更强联系导致与竞争替代音节相比，向该音节过渡的概率更高且延迟更短。然而，我们发现竞争性竞赛模型的模拟导致竞争结果的获胜时间分布重叠，并且无法复制歌声数据中发现的概率与间隔持续时间之间的强负相关。对歌声结构的进一步研究揭示了共享一个共同汇聚点的过渡的间隔持续时间之间存在强正相关。这样的过渡并非由共同的竞争过程相关联，而是反映了一个共同的结尾音节。与间隔持续时间相反，过渡概率在汇聚点处没有相关性。总之，我们的数据表明音节选择在间隔早期发生，间隔时间主要由音节起始的延迟决定。这可能是由一个过程导致的，在这个过程中，概率序列首先稳定下来，随后是更频繁演唱的音节的延迟缩短。Bengalese 雀类的歌声由音节的概率序列组成。先前的研究揭示了过渡概率与音节间间隔持续时间之间存在强负相关。我们在此表明，这种负相关与之前关于音节过渡时间由竞争替代方案之间的竞赛所支配的观点不一致。相反，数据表明音节选择在间隔早期发生，间隔时间主要由音节起始的延迟决定。
