Do children understand man’s best friend? Classification of dog barks by pre-adolescents and adults
Pongrácz P, Molnár Cs, Dóka A & Miklósi Á
Applied Animal Behaviour Science, 2011, 135, 95-102

Play back experiments compared the ability of children (aged 6, 8, and 10 years) and adults to discriminate dog barks recorded in three different contexts. Participants had to categorize barks according to recording context, and to characterize the inner states of dogs by relating barks to facial expression of humans. It was found that older children classified more barks correctly. Children in all groups classified barks at a Stranger significantly above chance level, however, only the ten-year-old children and adults could classify Play barks over the chance level. There were no significant differences between the groups performances in the inner state characterization task. Stranger barks were considered as more angry, while Alone barks were indicated as being more fearful. In the case of Play barks, participants had more difficulties in characterization. Overall we found only slight differences between the performances of preschoolers and adults. This shows that the ability of understanding basic inner states of dogs on the basis of acoustic signals is present in humans from a very young age. These results are in sharp contrast with other reports in the literature which showed that young children tend to misinterpret canine visual signals.

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Media reflections to this study.

Seeing with ears: Sightless humans’ perception of dog bark provides a test for structural rules in vocal communication
Molnár Cs, Pongrácz P & Miklósi Á
Quarterly Journal of Experimental Psychology, 2010, 63, 1004-1013

Prerecorded family dog (Canis familiaris) barks were played back to groups of congenitally sightless, sightless with prior visual experience, and sighted people (none of whom had ever owned a dog). We found that blind people without any previous canine visual experiences can categorize accurately various dog barks recorded in different contexts, and their results are very close to those of sighted people in characterizing the emotional content of barks. These findings suggest that humans can recognize some of the most important motivational states reflecting, for example, fear or aggression in a dog’s bark without any visual experience. It is very likely that this result can be generalized to other mammalian species – that is, no visual experience of another individual is needed for recognizing some of the most important motivational states of the caller.

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Dogs discriminate between barks: The effect of context and identity of the caller
Molnár Cs, Pongrácz P, Faragó T, Dóka A & Miklósi Á
Behavioural Processes, 2009, 82, 198-201

In the present study we explored whether dogs (Canis familiaris) are able to discriminate between conspecific barks emitted in different contexts recorded either from the same or different individuals. Playback experiments were conducted with dogs using barks as stimuli in a habituation-dishabituation paradigm. Barks were recorded in two contexts (stranger at the fence and when the dog was left alone) from different individuals. We found that dogs distinguished between barks emitted in these two contexts and were also able to discriminate between different individuals which were barking in the same context. These findings suggest that dog bark may carry context- and individual-specific information for the conspecifics.

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Barking in family dogs: An ethological approach
Pongrácz P, Molnár Cs & Miklósi Á
The Veterinary Journal, 2010, 183, 141-147

Although it is one of the most conspicuous features of dog behaviour, barking has received little attention from ethologists or from an applied perspective. In this review, an ethological look is taken at the communicative aspect of dog barking. Emerging new research has indicated that in the repertoire of dog vocalisations barking has unique features in showing wide ranges of acoustic parameters, such as frequency, tonality and rhythmicity. Barking has been shown to be context dependent, and provides information for humans about the inner state of the dog although there are few indications that barking is used for intra-species communication. It is assumed that dog barking emerged through selective processes in which human preferences for certain acoustic aspects of the vocalisation may have been paramount. A more experiment-oriented approach is required for the study of dog vocalisation that could shed light on the possible communicative function of these acoustic signals.

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Classification of dog barks: a machine learning approach
Molnár Cs, Kaplan F, Roy P, Pachet F, Pongrácz P, Dóka A & Miklósi Á
Animal Cognition, 2008, 11, 389-400

In this study we analyzed the possible contextspecific and individual-specific features of dog barks using a new machine-learning algorithm. A pool containing more than 6,000 barks, which were recorded in six different communicative situations was used as the sound sample. The algorithm’s task was to learn which acoustic features of the barks, which were recorded in different contexts and from different individuals, could be distinguished from another. The program conducted this task by analyzing barks emitted in previously identified contexts by identified dogs. After the best feature set had been obtained (with which the highest identification rate was achieved), the efficiency of the algorithm was tested in a classification task in which unknown barks were analyzed. The recognition rates we found were highly above chance level: the algorithm could categorize the barks according to their recorded situation with an efficiency of 43% and with an efficiency of 52% of the barking individuals. These findings suggest that dog barks have context-specific and individual-specific acoustic features. In our opinion, this machine learning method may provide an efficient tool for analyzing acoustic data in various behavioral studies.

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This study has gained some interest in public media. See articles in several languages.

Dogs can discriminate barks from different situations
Maros, K, Pongrácz P, Bárdos Gy, Molnár Cs, Faragó T & Miklósi Á
Applied Animal Behaviour Science, 2008, 114, 159-167

We investigated if dogs can discriminate barks of another individual recorded in two markedly different situations: (a) when a stranger entered the property where the dog lived, and (b) when the dog was tethered to a tree and left alone. We used a habituation-dishabituation paradigm for testing discriminatory abilities. Three 25-s long samples of “stranger” bark were followed by a single “alone” bark sample. As a control, we used two types of mechanical noise (an electric drill and a refrigerator). Dogs (n = 14) were equipped with a portable heart rate monitor which recorded the data during the whole experiment. Upon hearing the first barking sound, the heart rate of the dogs increased significantly, followed by a habituation when the same barks were played back the second and third time. The fourth, different bark caused dishabituation of the heart rate. This suggests that heart rate can be a sensitive indicator of changes in attentiveness. The dogs did not show any significant evidence of dishabituation to the Control condition of the mechanical noises. Our experiment showed that dogs can perceive the difference between barks originating from different situations, thus barking is perhaps a communicative tool not only for dogs to humans, but for dogs to dogs as well.

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A New Scientist article about this study here (might require subscription).

Can humans discriminate between dogs on the base of the acoustic parameters of barks?
Molnár Cs, Pongrácz P, Dóka A & Miklósi Á
Behavioural Processes, 2006, 73, 76-83

In this study we tested the often suggested claim that people are able to recognize their dogs by their barks. Earlier studies in other species indicated that reliable discrimination between individuals cannot be made by listening to chaotically noisy vocalizations. As barking is typically such a chaotic noisy vocalization, we have hypothesized that reliable discrimination between individuals is not possible by listening to barks. In this study, playback experiments were conducted to explore (1) how accurately humans discriminate between dogs by hearing only their barks, (2) the impact of the eliciting context of calls on these discrimination performances, and (3) how much such discrimination depends on acoustic parameters (tonality and frequency of barks, and the intervals between the individual barks). Our findings were consistent with the previous studies: human performances did not pass the empirical threshold of reliable discrimination in most cases. But a significant effect of tonality was found: discrimination between individuals was more successful when listeners were listening to low harmonic-to-noise ratio (HNR) barks. The contexts in which barks were recorded affected significantly the listeners’ performances: if the dog barked at a stranger, listeners were able to discriminate the vocalizations better than if they were listening to sounds recorded when the dog was separated from its owner. It is rendered probable that the bark might be a more efficient communication system between humans and dogs for communicating the motivational state of an animal than for discrimination among strange individuals.

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Acoustic parameters of dog barks carry emotional information for humans
Pongrácz P, Molnár Cs & Miklósi Á
Applied Animal Behaviour Science, 2006, 100, 228-240

In an earlier study, we found that humans were able to categorize dog barks correctly, which were recorded in various situations. The acoustic parameters, like tonality, pitch and inter-bark time intervals, seemed to have a strong effect on how human listeners described the emotionality of these dog vocalisations. In this study, we investigated if the effect of the acoustic parameters of the dog bark is the same on the human listeners as we would expect it from studies in other mammalian species (for example, low, hoarse sounds indicating aggression; high pitched, tonal sounds indicating subordinance/ fear). People with different experience with dogs were asked to describe the emotional content of several artificially assembled bark sequences on the basis of five emotional states (aggressiveness, fear, despair, playfulness, happiness). The selection of the barks was based on low, medium and high values of tonality and peak frequency. For assembling artificial bark sequences, we used short, middle or long inter-bark intervals. We found that humans with different levels of experience with dogs described the emotional content of the bark sequences quite similarly, and the extent of previous experience with the given breed (Mudi), or with dogs in general, did not cause characteristic differences in the emotionality scores. The scoring of the emotional content of the bark sequences was in accordance with the so-called Morton’s structural-acoustic rules. Thus, low pitched barks were described as aggressive, and tonal and high pitched barks were scored as either fearful or desperate, but always without aggressiveness. In general, tonality of the bark sequence had much less effect than the pitch of the sounds. We found also that the inter-bark intervals had a strong effect on the emotionality of dog barks for the human listeners: bark sequences with short inter-bark intervals were scored as aggressive, but bark sequences with longer inter-bark intervals were scored with low values of aggression. High pitched bark sequences with long inter-bark intervals were considered happy and playful, independently from their tonality. These findings show that dog barks function as predicted by the structural-motivational rules developed for acoustic signals in other species, suggesting that dog barks may present a functional system for communication at least in the dog-human relationship. In sum it seems that many types of different emotions can be expressed with the variation of at least three acoustic parameters.

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Media reflection to this study.

Human Listeners Are Able to Classify Dog (Canis familiaris) Barks Recorded in Different Situations 
Pongrácz P, Molnár Cs, Miklósi Á & Csányi V
Journal of Comparative Psychology, 2005, 119, 136-144

The authors investigated whether human listeners could categorize played-back dog (Canis familiaris) barks recorded in various situations and associate them with emotional ratings. Prerecorded barks of a Hungarian herding dog breed (Mudi) provided the sample. Human listeners were asked to rate emotionality of the vocalization and to categorize the situations on the basis of alternative situations provided on a questionnaire. The authors found almost no effect of previous experience with the given dog breed or of owning a dog. Listeners were able to categorize bark situations high above chance level. Emotionality ratings for particular bark samples correlated with peak and fundamental frequency and interbark intervals. The authors did not find a significant effect of tonality (harmonic-to-noise ratio) on either the emotionality rating or situation categorization of the human listeners. Humans’ ability to recognize meaning suggests that barks could serve as an effective means of communication between dog and human.

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