Until recently, the barks of domesticated dogs were thought to have little to no communicative function (Cohen and Fox, 1976). In the last article I reviewed, I summarized Pongracz et al.’s (2005) finding that people can discriminate between, and accurately characterize dog barks. This suggests that dog barks have communicative value to humans. While this study is not perfect (discussed previously), I want to know how dogs react to barks, and whether a bark has intraspecies communicative value. I found the following article by Maros, Pongracz, Bardos, Molnar, Farago´, and Miklosi (2008) that suggests pet dogs can at least discriminate between barks emitted in different contexts.

The goal of the study was to determine if barking transmits information to a listening dog. To do this, the authors used a habituation-dishabituation paradigm consisting of two types of barks, and recorded corresponding changes in heart rate (HR) elicited by each bark. They played one type of bark 3 times and predicted the receiver, listener, would react less (have a decreased HR) with each presentation. A decrease in response over time is termed habituation. Maros et al. (2008) then played a different type of bark. If the HR response elicited by the original bark was restored with the different bark, than dishabituation occurred. The authors considered a dishabituated response an indicator of discrimination between the two types of barks by the listening dog.

Procedure

Before the start of the study the authors prerecorded the barks of male and female dogs in two different contexts: 1) Stranger - unknown person in yard and 2) Alone - dog tied to a tree. Both barks having different acoustic features. They also recorded control sounds consisting of two types of mechanical noises, a drill and a refrigerator.

Thirty minutes before testing, pet dogs were fitted with a HR monitor. Dogs were then tested using the habituation–dishabituation paradigm described previously. They heard playbacks of prerecorded sounds from one of two conditions: bark or mechanical noises. The following is an example of what a dog may have heard in the bark condition. During the habituation phase dogs heard 3 different barks from the same dog recorded in one context (i.e. Stranger). In the dishabituation phase dogs heard 1 bark from the same dog but recorded in the other context (i.e. Alone). The procedure was identical for the mechanical noise condition. The order in which the bark or mechanical noise condition where heard, varied randomly. A half hour separated each test condition. The authors then compared HRs elicited during the bark condition to the HRs elicited during the mechanical noise condition.

Results/Conclusion

Based on changes in HR, Maros et al. (2008) found that HR decreased with repeated playbacks to barks recorded in the same context (habituation), HR increased with playback of the bark in the other context (dishabituation), and HR did not increase with playback of a new mechanical noise (no dishabituation). By measuring changes in HR, the authors showed dogs habituate to different samples from the same context, and can discriminate between barks from different contexts. This was not true for the mechanical noise condition as HR did not change.

Discussion

This study suggests dogs are capable of distinguishing between barks emitted in different contexts. While this is good information, I want to know what the dogs did (their behavior) when they heard the barks. Did the dogs show fear postures, remain neutral, or become offensive? Maybe the dogs showed no discernible change in behavior. Looking at their heart rates, this might be the case. Baseline HR was 93 BPM in both conditions. In the bark condition, the maximum average HR hit 103 BPM. In the mechanical noise condition, the maximum average HR never rose above 93 BPM. Seeing such low heart rates makes me question the validity of this study. In my experience, only dogs with solid temperaments have a HR this low in an unfamiliar place, something hard to find in a pet dog. I suppose it’s possible that these dogs were very calm throughout testing, however the data don’t add up to me. Personally, I’m not impressed by an increase in HR of 10 BPM. With the change in HR being so small, and no report of behavior before and after the barks, what criteria did the authors use to decide the dogs heard the noises? Overall I think this was a poorly designed study.

However, I really like that Maros et al. (2008) used HR monitors. My friend and mentor, Nancy Williams, studies HR and heart rate variability (HRV) in dogs. Her research (something I’ll definitely write about in the future) suggests moment-to-moment changes in a dog’s HR, elicited by a stimulus, predict a behavioral response. With this information, she has developed innovative techniques for modifying the behavior of fearful, anxious, and aggressive dogs that keep the dog’s HR low. (Williams et al., 2003). More research needs to be done on this topic.

Anyways, thanks for learning with me. As always, I’m on the look out for high quality research. If you find something, let me know!

References

Cohen, J.A., Fox, M.W., 1976. Vocalization in wild canids and possible effects of domestication. Behavioural Processes, 1, 77–92.

Pongracz, P., Molnar, C., Miklosi, A., & Csanyi, V. (2005). Human listeners are able to classify dog (Canis familiaris) barks recorded in different situations. Journal of Comparative Psychology, 119(2), 136–144.

Maros, K., Pongracz, P., Bardos, G., Molnar, C., Farago´, T., Miklosi, A. (2008). Dogs can discriminate barks from different situations. Applied Animal Behaviour Science, 114, 159–167.

Williams, N. G., Borchelt, P. L., Sollers, J. J. 3rd, Gasper, P.W., & Thayer, J. F. (2003). Ambulatory monitoring of cardiovascular responses during behavioral modification of an aggressive dog. Biomedical Sciences Instrumentation, 39, 214-9.