Online Processing of Speech and Social Information in Early Word Learning

Online Processing of Speech and Social Information in Early Word Learning Daniel Yurovsky Anna Wade Michael C. Frank yurovsky@stanford.edu Department of Psychology Stanford University wadea@neurosurg.ucsf.edu Department of Neurological Surgery University of California, San Francisco mcfrank@stanford.edu Department of Psychology Stanford University Abstract Although word learning unfolds over days, weeks, and months, individual naming events are over in a matter of seconds. To benefit from a naming event, children must at least hear the la- bel and see the referent. We tested 1-, 2- , 3-, and 4-year old children in a naturalistic word learning task with two condi- tions: one that taxed both speech processing and rapid gaze- following, and one in which a social cue-to-reference was available for an extended time. The development of word- learning in the extended condition paralleled the development of speech processing, but learning in the brief condition lagged behind. However, learning from both the brief and extended cues was predicted by individual differences in speech pro- cessing and cue-following together. Thus, even through the 4th year, real-time processing of social and linguistic informa- tion are a critical bottleneck for word learning. Keywords: Language acquisition, word learning, attention, social cues, development Introduction Language learning is a fundamentally social endeavor – it relies critically on input from social partners. This is be- cause many aspects of natural languages, like the mappings between words and their referents, are conventions that can vary from community to community (Chater & Christiansen, 2010). To learn their first words, children must track the re- lationship between the sounds that speakers produce and the things in their world (Pinker, 1984; Siskind, 1996). Not everything about a word and its referents needs to be learned in a single shot. Instead, it is likely that this rela- tionship is refined over multiple exposures, over a period of days, weeks or months (Carey & Bartlett, 1978; Smith & Yu, 2008; McMurray, Horst, & Samuelson, 2012). Nonetheless, each individual naming event occurs in real-space and real- time (Samuelson, Smith, Perry, & Spencer, 2011; Spencer, Perone, Smith, & Samuelson, 2011). If a child does not hear the label, or does not see the target referent, the informa- tion “available” in the naming event is effectively unavailable to the child (Yu & Smith, 2012; Yurovsky, Smith, & Yu, in press). Thus, a critical bottleneck in language acquisition is the ability to process the right information at the right time (Fernald & Marchman, 2012). Young children are slow processors of both speech and vi- sual input (Kail, 1991; Fernald, Pinto, Swingley, Weinberg, & McRoberts, 1998). They are also slow to re-deploy their at- tention in response to changing visual information (Colombo, 2001). Thus, it is perhaps unsurprising that the properties of child-directed speech and child-directed actions seem well- designed to scaffold slow processors. Child-directed utter- ances are slower, shorter, and have larger pitch contours than do utterances spoken to adults. Repetition is common in child-directed speech, and key words are made more salient through minor local variations (Onnis, Waterfall, & Edelman, 2008). In addition, new labels are often introduced through a small set of common naming phrases that facilitate attention tom and learning of, new words (Fernald & Hurtado, 2006; Yurovsky, Yu, & Smith, 2012). Exposure to these kind of structure makes a real difference, predicting individual dif- ferences in vocabulary development (Hoff, 2003). Child- directed actions are similarly exaggerated, marked by big- ger, simpler, and more repetitive movements (Brand, Bald- win, & Ashburn, 2002). Indeed, multi-modal synchrony be- tween these exaggerated visual and auditory inputs may be precisely the the information that young children use to to learn their first words (Gogate, Bahrick, & Watson, 2000). However, while social partners may sometimes scaffold young language learners, simplifying their speech and tim- ing their naming events so that labels coincide with the focus of children’s visual attention, this kind of pedagogical nam- ing likely accounts for a minority of the relevant input from which words and their referents could be learned. For in- stance, while isolated words facilitate speech processing and word learning, they make up less than 10% of all speech to children (Brent & Siskind, 2001). Similarly, referential expressions produced while children are already looking at the target object facilitate word learning, but make up only a portion of the naming events produced to young children (Tomasello & Farrar, 1986; Frank, Tenenbaum, & Fernald, 2013). In the remaining naming events, successful learn- ing requires the child to check with the speaker to determine the target of her reference (Baldwin, 1991). Consequently, the ability to quickly process speech, and to quickly follow a speaker’s social cues, should both give learners access to more and more useful information. Over the first two years, children make rapid gains in the rate at which they process auditory input, picking referen- tial words out of continuous speech (Fernald et al., 1998). During this time, individual differences in rate of spoken lan- guage processing predict individual differences in vocabulary size (Fernald, Perfors, & Marchman, 2006). Over the same two year period, children also improve in their abilities to at- tend to and use social cues indicating the target of a speaker’s reference (Scaife & Bruner, 1975; Hollich, Hirsh-Pasek, & Golinkoff, 2000). As with speech processing, individual dif- ferences in children’s gaze- and point-following predict their language development over these two years (Brooks & Melt- zoff, 2006). But, while the second year is marked by an increase in the rate at which children learn new words, this acceleration in