Dog brains are sensitive to infant- and dog-directed prosody.

When addressing preverbal infants and family dogs, people tend to use specific speech styles. While recent studies suggest acoustic parallels between infant- and dog-directed speech, it is unclear whether dogs, like infants, show enhanced neural sensitivity to prosodic aspects of speech directed to them. Using functional magnetic resonance imaging on awake unrestrained dogs we identify two non-primary auditory regions, one that involve the ventralmost part of the left caudal Sylvian gyrus and the temporal pole and the other at the transition of the left caudal and rostral Sylvian gyrus, which respond more to naturalistic dog- and/or infant-directed speech than to adult-directed speech, especially when speak by female speakers. This activity increase is driven by sensitivity to fundamental frequency mean and variance resulting in positive modulatory effects of these acoustic parameters in both aforementioned non-primary auditory regions. These findings show that the dog auditory cortex, similarly to that of human infants, is sensitive to the acoustic properties of speech directed to non-speaking partners. This increased neuronal responsiveness to exaggerated prosody may be one reason why dogs outperform other animals when processing speech.

The acoustic bases of human voice identity processing in dogs.

Speech carries identity-diagnostic acoustic cues that help individuals recognize each other during vocal-social interactions. In humans, fundamental frequency, formant dispersion and harmonics-to-noise ratio serve as characteristics along which speakers can be reliably separated. The ability to infer a speaker's identity is also adaptive for members of other species (like companion animals) for whom humans (as owners) are relevant. The acoustic bases of speaker recognition in non-humans are unknown. Here, we tested whether dogs can recognize their owner's voice and whether they rely on the same acoustic parameters for such recognition as humans use to discriminate speakers. Stimuli were pre-recorded sentences spoken by the owner and control persons, played through loudspeakers placed behind two non-transparent screens (with each screen hiding a person). We investigated the association between acoustic distance of speakers (examined along several dimensions relevant in intraspecific voice identification) and dogs' behavior. Dogs chose their owner's voice more often than that of control persons', suggesting that they can identify it. Choosing success and time spent looking in the direction of the owner's voice were positively associated, showing that looking time is an index of the ease of choice. Acoustic distance of speakers in mean fundamental frequency and jitter were positively associated with looking time, indicating that the shorter the acoustic distance between speakers with regard to these parameters, the harder the decision. So, dogs use these cues to discriminate their owner's voice from unfamiliar voices. These findings reveal that dogs use some but probably not all acoustic parameters that humans use to identify speakers. Although dogs can detect fine changes in speech, their perceptual system may not be fully attuned to identity-diagnostic cues in the human voice.

Social relationship-dependent neural response to speech in dogs.

In humans, social relationship with the speaker affects neural processing of speech, as exemplified by children's auditory and reward responses to their mother's utterances. Family dogs show human analogue attachment behavior towards the owner, and neuroimaging revealed auditory cortex and reward center sensitivity to verbal praises in dog brains. Combining behavioral and non-invasive fMRI data, we investigated the effect of dogs' social relationship with the speaker on speech processing. Dogs listened to praising and neutral speech from their owners and a control person. We found positive correlation between dogs' behaviorally measured attachment scores towards their owners and neural activity increase for the owner's voice in the caudate nucleus; and activity increase in the secondary auditory caudal ectosylvian gyrus and the caudate nucleus for the owner's praise. Through identifying social relationship-dependent neural reward responses, our study reveals similarities in neural mechanisms modulated by infant-mother and dog-owner attachment.

Longitudinal Volumetric Assessment of Ventricular Enlargement in Pet Dogs Trained for Functional Magnetic Resonance Imaging (fMRI) Studies.

BACKGROUND: Recent studies suggest that clinically sound ventriculomegaly in dogs could be a preliminary form of the clinically significant hydrocephalus. We evaluated changes of ventricular volumes in awake functional magnetic resonance imaging (fMRI) trained dogs with indirectly assessed cognitive abilities over time (thus avoiding the use of anaesthetics, which can alter the pressure). Our research question was whether ventricular enlargement developing over time would have any detrimental effect on staying still while being scanned; which can be extrapolated to the ability to pay attention and to exert inhibition. METHODS: Seven healthy dogs, 2-8 years old at the baseline scan and 4 years older at rescan, participated in a rigorous and gradual training for staying motionless (<2 mm) in the magnetic resonance (MR) scanner without any sedation during 6 minute-long structural MR sequences. On T1 structural images, volumetric analyses of the lateral ventricles were completed by software guided semi-automated tissue-type segmentations performed with FMRIB Software Library (FSL, Analysis Group, Oxford, UK). RESULTS AND CONCLUSION: We report significant enlargement for both ventricles (left: 47.46 %, right: 46.07 %) over time while dogs retained high levels of attention and inhibition. The results suggest that even considerable ventricular enlargement arising during normal aging does not necessarily reflect observable pathological changes in behavior.

Multilevel fMRI adaptation for spoken word processing in the awake dog brain.

Human brains process lexical meaning separately from emotional prosody of speech at higher levels of the processing hierarchy. Recently we demonstrated that dog brains can also dissociate lexical and emotional prosodic information in human spoken words. To better understand the neural dynamics of lexical processing in the dog brain, here we used an event-related design, optimized for fMRI adaptation analyses on multiple time scales. We investigated repetition effects in dogs' neural (BOLD) responses to lexically marked (praise) words and to lexically unmarked (neutral) words, in praising and neutral prosody. We identified temporally and anatomically distinct adaptation patterns. In a subcortical auditory region, we found both short- and long-term fMRI adaptation for emotional prosody, but not for lexical markedness. In multiple cortical auditory regions, we found long-term fMRI adaptation for lexically marked compared to unmarked words. This lexical adaptation showed right-hemisphere bias and was age-modulated in a near-primary auditory region and was independent of prosody in a secondary auditory region. Word representations in dogs' auditory cortex thus contain more than just the emotional prosody they are typically associated with. These findings demonstrate multilevel fMRI adaptation effects in the dog brain and are consistent with a hierarchical account of spoken word processing.

Repetition enhancement to voice identities in the dog brain.

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.

On the Face of It: No Differential Sensitivity to Internal Facial Features in the Dog Brain.

Dogs are looking at and gaining information from human faces in a variety of contexts. Next to behavioral studies investigating the topic, recent fMRI studies reported face sensitive brain areas in dogs' temporal cortex. However, these studies used whole heads as stimuli which contain both internal (eyes, nose, mouth) and external facial features (hair, chin, face-outline). Behavioral studies reported that (1) recognition of human faces by dogs requires visibility of head contour and that (2) dogs are less successful in recognizing their owners from 2D pictures than from real human heads. In contrast, face perception in humans heavily depends on internal features and generalizes to 2D images. Whether putative face sensitive regions in dogs have comparable properties to those of humans has not been tested so far. In two fMRI experiments, we investigated (1) the location of putative face sensitive areas presenting only internal features of a real human face vs. a mono-colored control surface and (2) whether these regions show higher activity toward live human faces and/or static images of those faces compared to scrambled face images, all with the same outline. In Study 1 (n = 13) we found strong activity for faces in multiple regions, including the previously described temporo-parietal and occipital regions when the control was a mono-colored, homogeneous surface. These differences disappeared in Study 2 (n = 11) when we compared faces to scrambled faces, controlling for low-level visual cues. Our results do not support the assumption that dogs rely on a specialized brain region for processing internal facial characteristics, which is in line with the behavioral findings regarding dogs inability to recognize human faces based on these features.

Dogs can sense weak thermal radiation.

The dog rhinarium (naked and often moist skin on the nose-tip) is prominent and richly innervated, suggesting a sensory function. Compared to nose-tips of herbivorous artio- and perissodactyla, carnivoran rhinaria are considerably colder. We hypothesized that this coldness makes the dog rhinarium particularly sensitive to radiating heat. We trained three dogs to distinguish between two distant objects based on radiating heat; the neutral object was about ambient temperature, the warm object was about the same surface temperature as a furry mammal. In addition, we employed functional magnetic resonance imaging on 13 awake dogs, comparing the responses to heat stimuli of about the same temperatures as in the behavioural experiment. The warm stimulus elicited increased neural response in the left somatosensory association cortex. Our results demonstrate a hitherto undiscovered sensory modality in a carnivoran species.

Interspecific voice discrimination in dogs.

BACKGROUND AND AIMS: Conspecific individual recognition using vocal cues has been shown in a wide range of species but there is no published evidence that dogs are able to recognize their owner based on his/her voice alone (interspecific individual recognition). METHODS: In our test, dogs had to rely on vocal cues to find their hidden owner in a two-way choice task. From behind an opaque screen, both the owner and a control person uttered neutral speech (reading sentences from a receipt) before the dogs were allowed to make their choice. Correct choices were reinforced by food and by verbal praise. RESULTS: During the six-choice trials, dogs chose their owner's voice significantly more often than the control person's voice. There was no effect of learning throughout the trials, and dogs did not show side preference. DISCUSSION: Thus, dogs are able to discriminate interspecific voices, suggesting that they are able to identify their owner based on vocal cues alone. This experimental design allows exploration of the role of individual acoustic parameters (such as fundamental frequency) in voice discrimination.