To learn words, humans extract statistical regularities from speech. Multiple species use statistical learning also to process speech, but the neural underpinnings of speech segmentation in non-humans remain largely unknown. Here, we investigated computational and neural markers of speech segmentation in dogs, a phylogenetically distant mammal that efficiently navigates humans’ social and linguistic environment. Using electroencephalography (EEG), we compared event-related responses (ERPs) for artificial words previously presented in a continuous speech stream with different distributional statistics. Results revealed an early effect (220–470 ms) of transitional probability and a late component (590–790 ms) modulated by both word frequency and transitional probability. Using fMRI, we searched for brain regions sensitive to statistical regularities in speech. Structured speech elicited lower activity in the basal ganglia, a region involved in sequence learning, and repetition enhancement in the auditory cortex. Speech segmentation in dogs, similar to that of humans, involves complex computations, engaging both domain-general and modality-specific brain areas.
Whereas the present study showed that dogs can apply complex computations to segment a speech stream, the origin of this ability is less clear. The capacity for word segmentation could either reflect a general mammalian capacity that was previously undetected in other non-primate mammals or could be the result of effects of exposure or domestication. Although the design of the present study does not allow to disentangle these accounts, we did test whether individual differences in word segmentation capacity are influenced by dogs’ age (a potential though clearly imperfect proxy for exposure; cf. Salthouse 81 ) or head shape (an index of breeding that has been related to communicative cue-
reading abilities; cf. Bognár et al. 64,82 and Gácsi et al. 83 ), but we found no significant correlations with either factor. In future studies, domestication-related effects could be tested by comparing modern versus ancient breeds (differing in genetic ancestry 84 ) or similarly socialized wolves versus dogs 85–88 with comparable speech exposure.