Symbolic labelling in 5-month-old human infants

Abstract

Humans naturally entertain complex representations of the world based on various symbolic systems, from natural language to mathematical or musical notation. Above and beyond mere perceptual representations, the adult human mind can recode sensory inputs into abstract symbolic representations that can be internally manipulated and projected back onto the external world. However, the ontogeny of this striking ability remains controversial: Are children progressively acquiring symbolic representations through language acquisition, or are mental representations symbolic from the very beginning, language learning consisting in mapping mental symbols onto public symbols? Using high-density electroencephalography, we show here that preverbal infants can form mental representations that feature symbolic attributes. In three experiments, a total of 150 five month-olds were exposed to triplet words characterized by their abstract syllabic structure (AAB/ABA/ABB) consistently followed by an arbitrary label. Subsequently, incongruent structure-label pairings evoked a late violation-of-expectations signal, whereas congruent pairings induced an early priming effect. Importantly, the late surprise response was recorded for incongruent pairs even when the pairing order was reversed at test (i.e. labels preceding structure). Our results indicate that first, far beyond habituation/dishabituation, preverbal infants are able to recode sensory inputs, into abstract mental representations to which arbitrary labels can be flexibly assigned. Second, we demonstrate that, beyond conditioned associations, this mapping is instantly bidirectional. These findings buttress the hypothesis of symbolic representations in preverbal infants, which may serve as a foundation for our distinctively human learning abilities.\n\nSignificance StatementSymbolic systems provide a powerful tool for efficiently re-describing the world into operable mental variables that, in turn, become objects of cognitive manipulation. However, is this ability tied to mastering language? Using an associative learning task in preverbal infants, we show that 5 month-olds can re-describe percepts into abstract mental variables that can be associated with arbitrary labels, well before they produce their first words. Importantly, we show that, beyond associative learning, they readily inferred a bidirectional mapping between the re-described representations and the associated labels, a capacity that animals do not spontaneously exhibit. Human cognitive success might be rooted in such abstract recoding which is no longer sensitive to local variations, thus alleviating cognitive load, and ultimately facilitating learning.