Rogers Jack C, Davis Matthew H
MRC Cognition & Brain Sciences Unit, Cambridge, UK.
University of Birmingham.
J Cogn Neurosci. 2017 May;29(5):919-936. doi: 10.1162/jocn_a_01096. Epub 2017 Jan 27.
Speech perception and comprehension are often challenged by the need to recognize speech sounds that are degraded or ambiguous. Here, we explore the cognitive and neural mechanisms involved in resolving ambiguity in the identity of speech sounds using syllables that contain ambiguous phonetic segments (e.g., intermediate sounds between /b/ and /g/ as in "blade" and "glade"). We used an audio-morphing procedure to create a large set of natural sounding minimal pairs that contain phonetically ambiguous onset or offset consonants (differing in place, manner, or voicing). These ambiguous segments occurred in different lexical contexts (i.e., in words or pseudowords, such as blade-glade or blem-glem) and in different phonological environments (i.e., with neighboring syllables that differed in lexical status, such as blouse-glouse). These stimuli allowed us to explore the impact of phonetic ambiguity on the speed and accuracy of lexical decision responses (Experiment 1), semantic categorization responses (Experiment 2), and the magnitude of BOLD fMRI responses during attentive comprehension (Experiment 3). For both behavioral and neural measures, observed effects of phonetic ambiguity were influenced by lexical context leading to slower responses and increased activity in the left inferior frontal gyrus for high-ambiguity syllables that distinguish pairs of words, but not for equivalent pseudowords. These findings suggest lexical involvement in the resolution of phonetic ambiguity. Implications for speech perception and the role of inferior frontal regions are discussed.
语音感知和理解常常因需要识别退化或模糊的语音而受到挑战。在这里，我们使用包含模糊语音片段（例如，“blade”和“glade”中介于/b/和/g/之间的中间音）的音节，探索解决语音身份模糊性所涉及的认知和神经机制。我们使用音频变形程序创建了大量听起来自然的最小对立体，这些对立体包含语音上模糊的起始或结尾辅音（在发音部位、发音方式或浊音方面有所不同）。这些模糊片段出现在不同的词汇语境中（即单词或伪词中，如blade - glade或blem - glem）以及不同的音系环境中（即与词汇状态不同的相邻音节一起出现，如blouse - glouse）。这些刺激使我们能够探索语音模糊性对词汇判断反应（实验1）、语义分类反应（实验2）的速度和准确性以及在注意力理解过程中BOLD fMRI反应幅度（实验3）的影响。对于行为和神经测量，观察到的语音模糊性效应受到词汇语境的影响，导致区分单词对的高模糊性音节的反应变慢，并且左下额叶回的活动增加，但对于等效的伪词则不然。这些发现表明词汇参与了语音模糊性的解决。讨论了对语音感知的影响以及额叶下部区域的作用。
