Neural evidence for referential understanding of object words in dogs

Using words to refer to objects in the environment is a core feature of the human language faculty. Referential understanding assumes the formation of mental representations of these words.^1,2 Such understanding of object words has not yet been demonstrated as a general capacity in any non-human species,³ despite multiple behavior-based case reports.^{4,5,6,7,8,9,10} In human event-related potential (ERP) studies, object word knowledge is typically tested using the semantic violation paradigm, where words are presented either with their referent (match) or another object (mismatch).^11,12 Such mismatch elicits an N400 effect, a well-established neural correlate of semantic processing.^12,13 Reports of preverbal infant N400 evoked by semantic violations¹⁴ assert the use of this paradigm to probe mental representations of object words in nonverbal populations. Here, measuring dogs' (Canis familiaris) ERPs to objects primed with matching or mismatching object words, we found a mismatch effect at a frontal electrode, with a latency (206-606 ms) comparable to the human N400. A greater difference for words that dogs knew better, according to owner reports, further supported a semantic interpretation of this effect. Semantic expectations emerged irrespective of vocabulary size, demonstrating the prevalence of referential understanding in dogs. These results provide the first neural evidence for object word knowledge in a non-human animal. VIDEO ABSTRACT.