Communicative signals promote abstract rule learning by 7-month-old infants

Communicative signals promote abstract rule learning by 7-month-old infants Brock Ferguson (brock@u.northwestern.edu) Department of Psychology, Northwestern University, 2029 Sheridan Rd. Evanston, IL 60208 USA Casey Lew-Williams (clewwilliams@gmail.com) Department of Psychology, Princeton University, Peretsman-Scully Hall Princeton, NJ 08540 USA Abstract Infants’ ability to detect patterns in speech input is central to their acquisition of language, and recent evidence suggests that their cognitive faculties may be specifically tailored to this task: Seven-month-olds reliably abstract rule-like structures (e.g., ABB vs. ABA) from speech, but not other stimuli. Here we ask what drives this speech advantage. Specifically, we propose that infants’ learning from speech is driven by their representation of speech as a communicative signal. As evidence for this claim, we report an experiment in which 7-month-old infants (N=28) learned rules from a novel sound (sine-wave tones) introduced as a communicative signal, but failed to learn the same rules from tones presented in non-communicative contexts. These findings highlight the powerful influence of social-communicative contexts on infants’ learning. Keywords: language development; abstract rule learning; statistical learning; social cognition; grammar; infants Introduction The human capacity to learn language is unparalleled in the animal kingdom. Typically developing human infants efficiently learn the complexities of sounds, syllables, words, and sentences, but non-human animals – even those raised in rich linguistic environments – seem incapable of doing so (Pinker, 1994). What might explain this striking divide between humans and even our closest evolutionary cousins? One longstanding hypothesis is that humans have cognitive machinery dedicated to language acquisition (e.g., Chomsky, 1965; Pinker, 1994); however, identifying language- dedicated machinery has proven difficult. Several previous candidate language learning mechanisms – fast mapping of novel words, tracking transitional probabilities between syllables, and categorically perceiving speech – are now known to be engaged equally well by non-linguistic stimuli. In this paper, we assess the extent to which another candidate mechanism – abstract rule learning – is uniquely engaged by human speech. Specifically, we ask whether the well-documented “speech advantage” in rule learning might result from infants’ processing of speech per se, or whether it might result from infants’ attention to communicative signals including, but not limited to, speech. Abstract rule learning is the ability to extract generalizable regularities from a stream of input (Aslin & Newport, 2012). For example, given several sequences of syllables such as go-la-la, mu-fi-fi, and be-da-da, one might detect that all sequences follow an ABB rule (in which the latter two elements are identical and distinct from the former). This abstract rule contrasts with stimulus-specific rules (e.g., transitional probabilities, such as that la follows go 100% of the time, or that all sequences end with /a/) because one could recognize the instantiation of the abstract rule in an entirely novel sequence such as ci-ru-ru. Such generalizations are crucial to learning in many domains, but particularly in language acquisition. A hallmark of language proficiency is the ability to comprehend and produce novel utterances, and it seems that humans do so by generalizing rules (e.g., grammatical relations) and categories (e.g., semantic and syntactic groupings) from the linguistic input. Abstract rule learning in infancy appears to be specifically enhanced by speech. From seven months of age, infants reliably abstract simple ABB, AAB, and ABA rules from streams of spoken syllables (Gomez & Gerken, 1999; Marcus, Vijayan, Rao, & Vishton, 1999). In contrast, infants do not reliably abstract rules from non-speech auditory or visual stimuli (e.g., tones, animal sounds, geometric shapes; Johnson et al., 2009; Marcus, Fernandes, & Johnson, 2007). Even infants exposed to language in another modality (i.e., sign language) do not robustly uncover underlying rules (Rabagliati, Senghas, Johnson, & Marcus, 2012). These observations support the proposal that abstract rule learning may be a speech-tuned mechanism, and may help explain why human infants rapidly learn language while other species do not (Marcus & Rabagliati, 2008). Others have attempted to explain the “speech advantage” vis-a-vis abstract rule learning without appealing to cognitive adaptations for language. For example, speech may contain phonetic redundancies that guide infants towards an abstract rule (e.g., ABB) in ways that less redundant stimuli do not (Frank, Slemmer, Marcus, & Johnson, 2009a; Thiessen, 2012). Or, being a highly familiar signal, speech may be more efficiently processed relative to other stimuli and thus leave infants’ relatively limited cognitive resources free to uncover abstract rules