  Interpretability research has shown that self-supervised Spoken Language
Models (SLMs) encode a wide variety of features in human speech from the
acoustic, phonetic, phonological, syntactic and semantic levels, to speaker
characteristics. The bulk of prior research on representations of phonology has
focused on segmental features such as phonemes; the encoding of suprasegmental
phonology (such as tone and stress patterns) in SLMs is not yet well
understood. Tone is a suprasegmental feature that is present in more than half
of the world's languages. This paper aims to analyze the tone encoding
capabilities of SLMs, using Mandarin and Vietnamese as case studies. We show
that SLMs encode lexical tone to a significant degree even when they are
trained on data from non-tonal languages. We further find that SLMs behave
similarly to native and non-native human participants in tone and consonant
perception studies, but they do not follow the same developmental trajectory.
