Faculty of Social and Human Sciences, Universidad de Deusto, Bilbao, Spain.
Basque Foundation for Science Ikerbasque, Bilbao, Spain.
Dev Sci. 2024 Sep;27(5):e13533. doi: 10.1111/desc.13533. Epub 2024 Jun 9.
Infants begin to segment word forms from fluent speech-a crucial task in lexical processing-between 4 and 7 months of age. Prior work has established that infants rely on a variety of cues available in the speech signal (i.e., prosodic, statistical, acoustic-segmental, and lexical) to accomplish this task. In two experiments with French-learning 6- and 10-month-olds, we use a psychoacoustic approach to examine if and how degradation of the two fundamental acoustic components extracted from speech by the auditory system, namely, temporal (both frequency and amplitude modulation) and spectral information, impact word form segmentation. Infants were familiarized with passages containing target words, in which frequency modulation (FM) information was replaced with pure tones using a vocoder, while amplitude modulation (AM) was preserved in either 8 or 16 spectral bands. Infants were then tested on their recognition of the target versus novel control words. While the 6-month-olds were unable to segment in either condition, the 10-month-olds succeeded, although only in the 16 spectral band condition. These findings suggest that 6-month-olds need FM temporal cues for speech segmentation while 10-month-olds do not, although they need the AM cues to be presented in enough spectral bands (i.e., 16). This developmental change observed in infants' sensitivity to spectrotemporal cues likely results from an increase in the range of available segmentation procedures, and/or shift from a vowel to a consonant bias in lexical processing between the two ages, as vowels are more affected by our acoustic manipulations. RESEARCH HIGHLIGHTS: Although segmenting speech into word forms is crucial for lexical acquisition, the acoustic information that infants' auditory system extracts to process continuous speech remains unknown. We examined infants' sensitivity to spectrotemporal cues in speech segmentation using vocoded speech, and revealed a developmental change between 6 and 10 months of age. We showed that FM information, that is, the fast temporal modulations of speech, is necessary for 6- but not 10-month-old infants to segment word forms. Moreover, reducing the number of spectral bands impacts 10-month-olds' segmentation abilities, who succeed when 16 bands are preserved, but fail with 8 bands.
婴儿在 4 到 7 个月大时开始将流畅的言语分割成语词形式——这是词汇处理中的一项关键任务。先前的研究已经证实，婴儿依赖于言语信号中提供的各种线索（即韵律、统计、声学和词汇）来完成这项任务。在两项针对学习法语的 6 个月和 10 个月大婴儿的实验中，我们使用心理声学方法来研究语音中两个基本声学成分的退化是否以及如何影响词形分割，这两个基本声学成分由听觉系统提取，分别是时域（频率和幅度调制）和频谱信息。婴儿熟悉包含目标词的段落，在这些段落中，通过声码器用纯音替换频率调制（FM）信息，而幅度调制（AM）在 8 或 16 个频谱带中保留。然后，婴儿在目标词与新的控制词的识别测试中接受测试。虽然 6 个月大的婴儿在两种条件下都无法分割，但 10 个月大的婴儿成功了，尽管仅在 16 个频谱带条件下成功。这些发现表明，6 个月大的婴儿需要 FM 时域线索来进行语音分割，而 10 个月大的婴儿则不需要，尽管他们需要将 AM 线索呈现足够的频谱带（即 16 个）。这种在婴儿对频谱时间线索的敏感性方面观察到的发展变化可能是由于可用分割过程范围的增加，以及/或在两个年龄段之间的词汇处理中从元音偏向到辅音偏向的转变，因为元音受我们的声学操作影响更大。研究亮点：尽管将言语分割成语词形式对于词汇习得至关重要，但婴儿听觉系统提取来处理连续言语的声学信息仍然未知。我们使用声码化语音检查了婴儿在语音分割中的对频谱时间线索的敏感性，并在 6 到 10 个月大之间观察到了发展变化。我们表明，FM 信息，即言语的快速时域调制，对于 6 个月大但不是 10 个月大的婴儿来说是分割词形的必要条件。此外，减少频谱带的数量会影响 10 个月大婴儿的分割能力，当保留 16 个带时他们可以成功，而保留 8 个带时则会失败。
