Repetition enhancement to voice identities in the dog brain

Marianna Boros,Anna Gábor,Dóra Szabó,Attila Andics,Ferenc Szalay,Anett Bozsik,Tamás Faragó,Márta Gácsi

doi:10.1038/s41598-020-60395-7

Marianna Boros, Anna Gábor + Show 6 more

Open Access

https://doi.org/10.1038/s41598-020-60395-7

Copy DOI

Abstract

In the human speech signal, cues of speech sounds and voice identities are conflated, but they are processed separately in the human brain. The processing of speech sounds and voice identities is typically performed by non-primary auditory regions in humans and non-human primates. Additionally, these processes exhibit functional asymmetry in humans, indicating the involvement of distinct mechanisms. Behavioural studies indicate analogue side biases in dogs, but neural evidence for this functional dissociation is missing. In two experiments, using an fMRI adaptation paradigm, we presented awake dogs with natural human speech that either varied in segmental (change in speech sound) or suprasegmental (change in voice identity) content. In auditory regions, we found a repetition enhancement effect for voice identity processing in a secondary auditory region – the caudal ectosylvian gyrus. The same region did not show repetition effects for speech sounds, nor did the primary auditory cortex exhibit sensitivity to changes either in the segmental or in the suprasegmental content. Furthermore, we did not find evidence for functional asymmetry neither in the processing of speech sounds or voice identities. Our results in dogs corroborate former human and non-human primate evidence on the role of secondary auditory regions in the processing of suprasegmental cues, suggesting similar neural sensitivity to the identity of the vocalizer across the mammalian order.

Highlights

In the human speech signal, cues of speech sounds and voice identities are conflated, but they are processed separately in the human brain
On the whole-brain level, acoustic stimuli elicited extensive activity in bilateral temporal cortices encompassing the rostral, mid and caudal portions of the ectosylvian gyrus and a caudal portion of the Sylvian gyrus (Table 1 and Fig. 2). This contrast was used to identify group level peaks around which the sphere masks were built for the region of interest (ROI) analysis
This resulted in the selection of two peaks in the left hemisphere: one in the primary auditory cortex, the mid ectosylvian gyrus [−22, −16, 20] and one secondary auditory region, the caudal ectosylvian gyrus [−26, −24, 6]; and two peaks in the corresponding regions in the right hemisphere: mid ectosylvian gyrus [24, −18, 18] and caudal ectosylvian gyrus [24, −16, 2]

Summary

Introduction

In the human speech signal, cues of speech sounds and voice identities are conflated, but they are processed separately in the human brain. The same region did not show repetition effects for speech sounds, nor did the primary auditory cortex exhibit sensitivity to changes either in the segmental or in the suprasegmental content. Previous dog fMRI studies found no hemispheric bias for processing intonational cues in human speech[32], but the neural processing of segmental or speaker-related suprasegmental cues in non-primate species has not yet been tested systematically. We hypothesized that to humans, the analysis of these cues in dogs takes place at higher levels of the processing hierarchy, i.e. outside the primary auditory cortex If these cues are processed by separate mechanisms in the dog brain, these may be reflected in distinct repetition effects and/or hemispheric bias

Objectives

Methods

Results

Discussion

Conclusion