STUDY 4: THE IMPACT OF TEST REGISTER – 18- MONTH - OLD INFANTS LEARN

The final study of this dissertation reported in the paper by Schreiner and Mani (in revision) explored infants’ word segmentation and subsequent word learning abilities in order to assess the effect of pre-exposure on word learning. If infants benefit from an extended exposure in segmenting words from fluent IDS and ADS, a pre-exposure to the phonological form of a word might similarly impact infants’

abilities to add meaning to these previously segmented words, especially in regard to the ADS that infants start learning from relatively late. This again would considerably change our understanding of which kinds of language input infants are able to learn from.

CHAPTER 6: SUMMARY OF EMPIRICAL FINDINGS

Eighteen-month-old infants of the study were presented with the modified version of the preferential-listening task including a familiarization of a pseudoword, hereafter referred to as familiarized word, embedded in sentences. In the test phase, infants’ listening times to isolated tokens of the familiarized word and isolated tokens of a novel control word were measured. After a 5-minute interactive play phase with two different novel objects, infants participated in a word learning task. They were trained on two different word-object associations of which one label consisted of the familiarized word from the familiarization phase of the preferential-listening task and the other label consisted of a novel pseudoword that infants had never heard before.

Critically, infants were either trained in IDS or ADS. In the test phase, infants were presented with both objects from the training phase, side by side, and tested on their recognition of the previously learned word-object associations. Importantly, infants were tested in both IDS and ADS registers, regardless of the register of the training phase. The reason for using this method was to explore whether infants are unable to learn from speech samples presented in ADS in general or whether infants rather have difficulties in demonstrating their achievements when tested in the ADS register.

The results of this study suggest that infants were able to learn words regardless of the register they were trained in. That is, infants trained in IDS as well as infants trained in ADS had significantly higher PTLs towards the named object in the post-naming phase compared to the pre-naming phase, however, only if tested in the IDS register. Pre-exposure to the phonological word form in the preferential listening task did not seem to have an impact on infants’ word learning success.

In line with the findings from successful word learning from overheard ADS (Akhtar, Jipson, & Callanan, 2001; Gampe, Liebal, & Tomasello, 2012), the results of the fourth study of this dissertation also suggest that infants are able to learn from a much greater variety of input available to them than previously suggested, extending

CHAPTER 6: SUMMARY OF EMPIRICAL FINDINGS

the findings from word segmentation (Schreiner, Altvater-Mackensen, & Mani, 2016) to word learning (Schreiner & Mani, in revision). This study provides additional evidence that infants need to be attracted to language stimuli in order to learn. The fact that the register at test was critical to infants’ demonstration of their learning success underlines the importance of IDS in early language acquisition. Moreover, the longer times spent listening to IDS rather than ADS stimuli during the familiarization time of the preferential listening task support the idea of IDS as an attention-grabbing spotlight (Saint-Georges et al., 2013).

CHAPTER 7: DISCUSSION

Infants are exposed to language even before birth (DeCasper & Spence, 1986) and demonstrate remarkable language skills from very early on. However, most of the research to date has focused on language learning from a limited portion of the input available to infants. Against this background, the current thesis examined the range of possible inputs that infants are able to learn from and the extent to which language learning is impacted by both the type of exposure and the factors related to infants and mothers. Empirical investigations were conducted to investigate infants’

word segmentation and word learning abilities from different kinds of input. Critically, German-learning infants of the different studies were exposed to IDS, ADS, and exaggerated IDS that resembled the IDS style of American English.

There are two main conclusions that can be drawn from the studies presented in this dissertation. Firstly, infants are able to learn from ADS when exposed to this register of speech over an extended period of time. This suggests that infants are able to learn from a much larger repertoire of language input than previously assumed: Infants do not only learn from the small proportion of IDS directly addressed at the child but they may also learn from overheard input in the ADS register. This finding has important implications for our understanding of early language acquisition. In learning their first language, infants may be able to make use of all input. Even in the presence of adult conversations that are not directed at the infant, infants may overhear and use these adult-directed conversations for language learning. Secondly, young German infants don’t seem to be able to segment words from typical German IDS given short-term laboratory familiarization.

In the course of two studies, the difference in IDS modifications in German compared

CHAPTER 7: DISCUSSION

to American English was identified as a possible explanation for German infants’

failure to segment words from typical German IDS in short-term laboratory familiarization contexts. The magnitude of the differences between IDS and ADS in the two languages is identified as potential explanation for the cross-linguistic differences between German and American English infants’ segmentation abilities.

The first section of the discussion will explore the role of input in segmenting and learning new words. The second section will consider implications of the findings on current models of early language acquisition. Thirdly, the results will be examined in terms of infants’ generalization abilities, that is the flexibility with which infants recognize words despite variation within the speech signal. The fourth section will discuss the different methodological implications of neurophysiological measures and extended naturalistic home exposure that can be taken from this dissertation. Finally, suggestions for future research on early word segmentation and word learning from different kinds of input will be presented.

7.1. WORD SEGMENTATION AND WORD LEARNING FROM DIFFERENT