Much like changing the consonant or vowel in non-tonal languages functions to change the meaning of a word, in tonal languages (e.g., Mandarin Chinese, Thai), tones are also lexically contrastive. Further, similar success in minimal pair leaning has been observed for lexical tones (e.g., Graf Estes & Hay, 2015 Hay et al., 2015 Singh, Hui, Chan, & Golinkoff, 2014). For example, at 12 months English-learning infants are able to map words that differ in lexical stress (e.g., BEdoka vs deDOka) to novel objects ( Curtin, 2009). Work examining infants’ ability to map minimal-pairs that differ in suprasegmental features has revealed a different pattern of performance than the work on consonant-based minimal pairs. Consistent with this hypothesis, as infants gain language experience, they become more sensitive to phonetic differences in minimal pair words and show success in mapping them by 17–20 months of age ( Werker et al., 2002). One account of the difficulty 14-month-olds have mapping these types of minimal pairs is that infants of this age may not have strong, rapid access to minimally-distinctive phonemic contrasts during cognitively demanding word-learning tasks ( Werker & Curtin, 2005 for related evidence see Fennell, 2012 Fennell & Waxman, 2010 Yoshida et al., 2009). Follow-up studies have replicated this pattern of failure by 14-month-olds with numerous consonant-based minimal pairs (e.g., bin/ din, bin/ pin, pin/ din Pater, Stager, & Werker, 2004 buk/puk Rost & McMurray, 2009 daw/taw Thiessen, 2007) and some vowel-based minimal pairs (e.g., deet/doot and dit/doot Curtin, Fennell, & Escudero, 2009). Seminal work by Stager and Werker (1997) has suggested that even when sounds are lexically contrastive (i.e., they are used to differentiate word meaning in a given language) and are easily discriminated in an object-free task (i.e., when the words are presented with a checkerboard instead of an object), 14-month-old infants have a difficult time attending to the fine acoustic features in minimal pair object labels (e.g., bih and dih). In the current work, we aim to uncover why certain stimulus characteristics, specifically pitch contour information, support the mapping of labels to meaning by young learners. Thus, it is not immediately apparent why certain sounds are mapped to referents more easily than others. Further, at 14 months English-learning infants appear to have difficulty mapping labels that differ by a single consonant (e.g., minimal pairs bih and dih Stager & Werker, 1997) but succeed in mapping labels that minimally differ only in pitch contour (e.g., rising /ku/ and falling /ku/ Hay, Graf Estes, Wang, & Saffran, 2015). ooh, ssh) and sound sequences that do not conform to native-language phonotactic patterns (e.g., the Czech word ptak) as labels for novel objects, although, they continue to map phonotactically legal words even if they come from a different language (e.g., the Japanese words sika & hashi) ( MacKenzie, Curtin, & Graham, 2012 MacKenzie, Graham, & Curtin, 2011). For example, at 12 months English-learning infants reject distinct communicative vocal sounds (e.g. Further, even when researchers test infants of the same age and use the same basic methodologies, different patterns of results can emerge depending on characteristics of the labels used. There are many factors that affect infants’ ability to associate sounds with referents, including, but not limited to, infant characteristics (e.g., age & vocabulary size Werker, Fennell, Corcoran, & Stager, 2002) and task characteristics (e.g., referential support Fennell & Waxman, 2010 experimental design Yoshida, Fennell, Swingley, & Werker, 2009). Together, our findings suggest that multiple factors contribute to whether specific acoustic forms will function as candidate object labels.Īt its most basic level, word learning involves mapping sounds to meaning. We argue that experience with hearing and/or producing native language prosody may lead infants to initially over-interpret the role rising pitch plays in differentiating words. Instead, English-learning infants only learned if one of the labels had a rising pitch contour. In Experiment 2, we found that the degree of pitch variation in labels also does not account for learning. Conversely, infants readily mapped the less distinctive rising and dipping labels. Contrary to the salience hypothesis proposed in Experiment 1, English-learning 14-month-olds failed to map acoustically distinctive level and dipping labels to novel referents, even though they discriminated the labels when no potential referents were present. Here, we explore perceptual and experiential factors that drive associative learning of labels that differ in pitch contour. Infants show interesting patterns of flexibility and constraint early in word learning.
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