Decoding continuous speech in infancy

想象一下，一位母亲和她6个月大的孩子在看一只鸟啄人行道上的面包屑。妈妈说：看那只鸽子！那是一只鸽子。看到鸽子了吗？”后来，孩子和她爸爸在公园里吃午饭。一只鸟俯冲下来，落在他们旁边。爸爸开玩笑说：“我应该给鸽子一点我的泡菜吗？”在这个假设的例子中，孩子学到了什么？她能理解多少？她现在知道“鸽子”这个词了吗？这些问题看似简单，其实不然。正如我将在下面解释的那样，这个例子说明了我的研究计划旨在解决的一些关键理论问题。

Imagine a mom and her 6-month-old watching a bird peck at crumbs on the sidewalk. The mom says Look at the pigeon! That is a pigeon. See the pigeon?' Later, the child is having lunch with her dad in the park. A bird swoops down and lands next to them. Dad jokes Should I give the pigeon a smidgen of my pickle?' In this hypothetical example, what has the child learned? How much does she understand? Does she now know the word pigeon? These questions seem simple, but they are not. As I will explain below, this example illustrates some key theoretical issues my research program is designed to address. First, speech contains no reliable cues to word boundaries. Adults perceive speech as a string of discrete words only because they know how words typically sound. The lack of physical cues to word boundaries can be appreciated by listening to an unfamiliar language word boundaries blend together, obscuring where one word ends and the next begins. Thus, before we can ask whether the infant in this example understands pigeon', we must first ask whether they have extracted the word from their parents' utterances. Past work suggests that 6-month-olds do not yet do this, but I hypothesize that infants do segment out words when they are repeatedly aligned with an utterance edge (i.e. the Edge Hypothesis). Our hypothetical mom has done what moms often do when addressing their infants pigeon' is repeatedly positioned utterance-finally. Assuming the infant has segmented out pigeon', the next question is whether she will understand pigeon' when spoken by dad. 6-month-olds understand some words, so it is conceivable that the infant may understand pigeon when spoken by mom (especially if mom labels pigeons regularly). But whether or not the child will recognize and understand this word when spoken by dad is another question altogether. First, the dad places the word utterance-medially, making it hard to identify. Moreover, according to distributional models, the fact that dad also produces the syllable pih' in pickle' and gin' in smidgen' may lead the child to hypothesize that the syllables pih' and gin' are each a word. And finally, past research has shown that infants struggle with cross-gender word identification (i.e., a word learned in a female voice is recognized in another female voice, but hard to recognize in a male voice). And if mom and dad speak different variants of English (e.g., mom speaks Canadian English, dad speaks British English), this could complicate matters further. And yet, infants readily learn language despite these challenges. In my research, I ask: 1) How and when do infants segment words from speech? 2) How and when do infants learn to cope with speech variability? 3) What is the impact of being exposed to more than one variant of English? Answers to these questions will advance our theoretical understanding of infant development, and lay the groundwork for more applied advances in speech-language pathology.