# What Does That Head Tilt Mean? Brain Lateralization and Sex Differences in the Processing of Familiar Human Speech by Domestic Dogs

## TL;DR

Dogs tilt their heads when interacting with humans, possibly to process speech, with differences based on sex and direction of tilt.

## Contribution

This study reveals sex-based differences in head tilting in dogs, potentially linked to lateralized brain processing of human speech.

## Key findings

- Dogs tilt their heads more frequently in response to rich communicative cues from humans.
- Neutered male dogs tilt their heads more often than spayed females.
- Rightward head tilts suggest left-hemisphere language processing in dogs, similar to human patterns.

## Abstract

Dogs display many behaviors and expressions when interacting with human companions. Among these behaviors, people frequently observe dogs tilting their heads in one direction or the other when they are being spoken to. Despite being a commonly observed behavior, the origin and purpose of head-tilting in dogs is not well understood. In this study we use the DogFACS coding system coupled with AI analyses to review video recordings of household dogs responding to communication from their human owners. We examine head tilts to try to determine when and how dogs exhibit this behavior, and if it may be related to language processing. We find that communicative cues from people elicit more head tilting from dogs, and that there may be sex differences related to tilt frequency and directionality. Our findings have important implications for understanding human–dog interactions and language processing in non-human animals.

Does the head tilt observed in many domesticated dogs index lateralized language processing? To answer this question, the present study evaluated household dogs responding to four conditions in which owners provided an increasing number of communicative cues. These cues ranged from no communicative/affective cues to rich affective cues coupled with dog-directed speech. Dogs’ facial responses were first coded manually using the Dog Facial Action Coding System (DogFACS), followed by an in-depth investigation of head tilt behavior, in which AI-based automated analysis of head tilt and audio analysis of acoustic features extracted from communicative cues were implemented. In a sample of 103 dogs representing seven breed groups and mixed-breed dogs, we found significant differences in the number of head tilts occurring between conditions, with the most communicative (last) condition eliciting the most head tilts. There were also significant differences in the direction of the head tilts and between sex groups. Dogs were more likely to tilt their heads to the right, and neutered male dogs were more likely to tilt their heads than spayed female dogs. The right-tilt bias is consistent with left-hemisphere language processing in humans, with males processing language in a more lateralized manner, and females processing language more bilaterally—a pattern also observed in humans. Understanding the canine brain is important to both evolutionary research through a comparative lens, and in understanding our interspecies relationship.