Doctoral Dissertation Research: Predictability and Recoverability of High Vowel Reduction in Speech

人类的认知依靠直接和间接的信息来得出结论。依赖于直接信息的过程被称为自下而上的过程，即完全根据所提供的信息得出结论；依赖于间接信息的过程被称为自顶向下的过程，其中使用上下文、模式识别和概率等元素来形成对特定结果的期望。研究表明，强烈的自上而下的过程通常会阻碍刺激中某些信息的自下而上处理，但人们对这两种过程如何相互作用知之甚少。作为人类认知的一个组成部分，语言也表现出自上而下和自下而上过程的相互作用，在一种语言中有意义的差异在另一种语言中可能很容易被忽视。因此，语言是一种极好的工具，可以揭示大脑如何处理直接信息和间接信息。本研究以日语为个案进行研究。日语的音节结构绝大多数遵循简单的辅音-元音结构。然而，在日语中，不重读的元音/i， u/在两个不发音的辅音之间被弱化（例如，/suki/ [ski] 'like'），这通常会导致在发音过程中完全删除一个元音。然而，说日语的人经常报告在两个连续的无元音辅音之间感觉到一个元音，即使在完全没有元音的情况下（例如，[ski]被理解为/suki/）。目前还不清楚是什么导致了这种对显然不存在的元音的误解，但有两个可能的来源。第一种是间接来源。考虑到日语简单的音节结构，说日语的人习惯于在辅音之后看到元音，在这种情况下，对元音的误解可能是一个强大的自上而下的过程的结果。另一种选择是直接来源。因为在日语中元音的重读是很常见的，所以说日语的人甚至可能对暗示元音存在的细微声音信息都非常敏感，在这种情况下，对元音的感知将是自下而上过程的结果。生产实验和语料库研究将首先测试弱元音在自然产生的语音中存在哪些声学信息。然后，感知实验将对直接和间接信息进行处理，以测试这些日本听众在感知弱元音时更依赖哪一个。实验结果将为计算模型提供信息，该模型将研究如何学习对直接和间接线索的依赖。这些实验，连同这个模型，将使我们更深入地了解自下而上和自上而下的过程在多大程度上是由语言经验和更广泛的人类认知作为一个整体形成的。

Human cognition relies on direct and indirect information to draw conclusions. Processes that rely on direct information are called bottom-up processes, where a conclusion is drawn based solely on the provided information; processes that rely on indirect information are called top-down processes, where elements such as context, pattern-recognition, and probability are used to form an expectation for a particular outcome. Studies have shown that a strong top-down process often blocks bottom-up processing of certain information available in the stimulus, but how the two types of processes interact is poorly understood. As an integral part of human cognition, language also shows interactions of top-down and bottom-up processes, where differences that are meaningful in one language may be readily ignored as uninformative in another. Language, therefore, is an excellent tool for shedding light on how the processing of direct and indirect information interacts in the mind.This research focuses on Japanese as a case study. The syllable structure of Japanese overwhelmingly follows a simple consonant-vowel structure. However, the process of high vowel reduction in Japanese, where unaccented vowels /i, u/ are weakened between two voiceless consonants (e.g., /suki/ [ski] 'like'), often results in the complete deletion of a vowel during speech production. However Japanese speakers often report perceiving a vowel between two consecutive voiceless consonants, even in the complete absence of a vowel (e.g., [ski] perceived as /suki/). It is unclear at this point what drives this misperception of apparently non-existent vowels, but there are two likely sources. The first is an indirect source. Given the simple syllable structure of Japanese, Japanese speakers are conditioned to expect a vowel after a consonant, in which case the misperception of a vowel would be the result of a strong top-down process. The alternative is a direct source. Because high vowel reduction is common in Japanese, Japanese speakers may be hypersensitive even to subtle acoustic information that indicates the presence of a vowel, in which case the perception of a vowel would be the result of a bottom-up process. A production experiment and a corpus study will first test what acoustic information for a weakened vowel exists in naturally produced speech. A perception experiment will then manipulate the direct and indirect information to test which of these Japanese listeners rely on more when perceiving a weakened vowel. The experimental results will inform a computational model, which investigates how a reliance on the direct and indirect cues might be learned. The experiments, together with the model, will lead to a deeper understanding of the extent in which bottom-up and top-down processes are shaped by experience both in language and more broadly in human cognition as a whole.