Sensitivity to the sonority sequencing principle in rats (Rattus norvegicus)

Abstract

Albeit diverse, human languages exhibit universal structures. A salient example is the syllable, an important structure of language acquisition. The structure of syllables is determined by the Sonority Sequencing Principle (SSP), a linguistic constraint according to which phoneme intensity must increase at onset, reaching a peak at nucleus (vowel), and decline at offset. Such structure generates an intensity pattern with an arch shape. In humans, sensitivity to restrictions imposed by the SSP on syllables appears at birth, raising questions about its emergence. We investigated the biological mechanisms at the foundations of the SSP, testing a nonhuman, non-vocal-learner species with the same language materials used with humans. Rats discriminated well-structured syllables (e.g., pras) from ill-structured ones (e.g., lbug) after being familiarized with syllabic structures conforming to the SSP. In contrast, we did not observe evidence that rats familiarized with syllables that violate such constraint discriminated at test. This research provides the first evidence of sensitivity to the SSP in a nonhuman species, which likely stems from evolutionary-ancient cross-species biological predispositions for natural acoustic patterns. Humans' early sensitivity to the SSP possibly emerges from general auditory processing that favors sounds depicting an arch-shaped envelope, common amongst animal vocalizations. Ancient sensory mechanisms, responsible for processing vocalizations in the wild, would constitute an entry-gate for human language acquisition.

We are grateful to Martin Giurfa, Gonzalo Garcia-Castro and Andrea Ravignani for their feedbacks on this work. We also thank David M. Gómez for sharing the stimuli used in the neonate study. C.S. was supported by a Juan de la Cierva post-doctoral fellowship (IJC2019-041548-1/AEI/10.13039/501100011033). N.S.G. was supported by the project PID2021-123416NB-100/MICIN/AEI/10.13039/501100011033/FEDER UE financed by the Spanish Ministerio of Science and Innovation, State Research Agency and European Regional Development Fund. J.M.T was supported by the project PID2021-123973NB I00/MICIN/AEI/10.13039/501100011033/FEDER UE financed by the Spanish Ministerio of Science and Innovation, State Research Agency and European Regional Development Fund. N.S.G and J.M.T. were also supported by the project 2021 SGR 00911 financed by the Catalan Generalitat AGAUR.