Cognitive bias for learning speech sounds from a continuous signal space seems non-linguistic

When learning language, humans have a tendency to produce more extreme distributions of speech sounds than those observed most frequently: in rapid, casual speech, vowel sounds are centralized, yet cross-linguistically, peripheral vowels occur almost universally. We investigate whether adults’ generalization behaviour reveals selective pressure for communication when they learn skewed distributions of speech-like sounds from a continuous signals space. The domainspecific hypothesis predicts that the emergence of sound categories is driven by a cognitive bias to make these categories maximally distinct, resulting in more skewed distributions in participants’ reproductions. However, our participants showed more centred distributions, which goes against this hypothesis, indicating that there are no strong innate linguistic biases that affect learning these speech-like sounds. The centralization behaviour can be explained by a lack of communicative pressure to maintain categories.