Pet-directed speech (PDS) is often produced by humans when
addressing dogs. Similar to infant-directed speech, PDS is marked by a
relatively higher and more modulated fundamental frequency
(f
0) than is adult-directed speech. We tested
the prediction that increasing eye size in dogs, one facial feature of neoteny
(juvenilisation), would elicit exaggerated prosodic qualities or pet-directed
speech. We experimentally manipulated eye size in photographs of twelve dog
breeds by −15%, +15% and +30%. We first showed that dogs with larger eyes were
indeed perceived as younger. We then recorded men and women speaking towards
these photographs, who also rated these images for cuteness. Linear
mixed-effects models demonstrated that increasing eye size by 15% significantly
increased pitch range (f
0 range) and variability
(f
0CV) among women only. Cuteness ratings did
not vary with eye size, due to a possible ceiling effect across eye sizes. Our
results offer preliminary evidence that large eyes can elicit pet-directed
speech and suggest that PDS may be modulated by perceived juvenility rather than
cuteness. We discuss these findings in the context of inter-species vocal
communication.