By: Stephanie Pappas, LiveScience Senior Writer
Published: 06/08/2012 10:04 AM EDT on LiveScience

Plenty of pet owners are comforted by a pair of puppy-dog eyes or a swipe of the tongue when their dog catches them crying. Now, new research suggests that dogs really do respond uniquely to tears. But whether pets have empathy for human pain is less clear.

In a study published online May 30 in the journal Animal Cognition, University of London researchers found that dogs were more likely to approach a crying person than someone who was humming or talking, and that they normally responded to weeping with submissive behaviors. The results are what you might expect if dogs understand our pain, the researchers wrote, but it's not proof that they do.

"The humming was designed to be a relatively novel behavior, which might be likely to pique the dogs' curiosity," study researcher and psychologist Deborah Custance said in a statement. "The fact that the dogs differentiated between crying and humming indicates that their response to crying was not purely driven by curiosity. Rather, the crying carried greater emotional meaning for the dogs and provoked a stronger overall response than either humming or talking."

Humans domesticated dogs at least 15,000 years ago, and many a pet owner has a tale of their canine offering comfort in tough times. Studies have shown that dogs are experts at human communication, but scientists haven't been able to show conclusively that dogs feel empathy or truly understand the pain of others. In one 2006 study, researchers had owners fake heart attacks or pretend to be pinned beneath furniture, and learned that pet dogs failed to go for help (so much for Lassie saving Timmy from the well).

But seeking out assistance is a complex task, and Custance and her colleague Jennifer Mayer wanted to keep it simple. They recruited 18 pet dogs and their owners to test whether dogs would respond to crying with empathetic behaviors. The dogs included a mix of mutts, Labrador retrievers, golden retrievers and a few other common breeds. [What Your Dog's Breed Says About You]

The experiment took place in the owners' living rooms. Mayer would arrive and ignore the dog so that it would have little interest in her. Then she and the owner would take turns talking, fake-crying and humming.

Of the 18 dogs in the study, 15 approached their owner or Mayer during crying fits, while only six approached during humming. That suggests that it's emotional content, not curiosity, that brings the dogs running. Likewise, the dogs always approached the crying person, never the quiet person, as one might expect if the dog was seeking (rather than trying to provide) comfort.

"The dogs approached whoever was crying regardless of their identity. Thus they were responding to the person's emotion, not their own needs, which is suggestive of empathic-like comfort-offering behavior," Mayer said in a statement.

Of the 15 dogs that approached a crying owner or stranger, 13 did so with submissive body language, such as tucked tails and bowed heads, another behavior consistent with empathy (the other two were alert or playful). Still, the researchers aren't dog whisperers, and they can't prove conclusively what the dogs were thinking. It's possible that dogs learn to approach crying people because their owners give them affection when they do, the researchers wrote.

"We in no way claim that the present study provides definitive answers to the question of empathy in dogs," Mayer and Custance wrote. Nevertheless, they said, their experiment opens the door for more study of dogs' emotional lives, from whether different breeds respond to emotional owners differently to whether dogs understand the difference between laughter and tears.

Follow Stephanie Pappas on Twitter @sipappas or LiveScience @livescience. We're also on Facebook & Google+

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GALLERY: EXTREME ANIMALS
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  • Best Visual Effects

    <b>Nominees</b>: The glowing squid <i>Taningia danae</i>; the toothy and luminous Blackdragon fish; and the amazing <a href="http://www.livescience.com/16976-transparent-octopus-opaque-camouflage.html">transparent octopus</a> <i>Japetella heathi</i>. <b>And the winner is...</b> <i>Japetella heathi</i>. This deep-sea octopus possesses the amazing ability to switch from transparent to opaque and back again. In regular conditions, the octopuses are see-through, perhaps to prevent themselves as being seen as a dark silhouette against the ocean surface. But when bioluminescent light hits them, they instantaneously become pigmented, preventing a mirror-like glare from alerting potential predators to their existence. Well-played, <i>J. heathi</i>. Please limit your acceptance speech to 45 seconds.

  • Best Sound Mixing

    This technical prize goes to the animal that really brings it in the sound department. <b>Nominees:</b> The water boatman, for its incredibly loud genitals; the rumbling <a href="http://www.livescience.com/15966-mantis-shrimp-rumble.html">California mantis shrimp</a>; and the Emei music frog, for her beautiful love songs. <b>And the winner is</b> ... The water boatman. This itsy-bitsy insect is the loudest creature on Earth relative to body size, and boy does he pull it off in the weirdest way. Male water boatman <a href="http://www.livescience.com/14869-loudest-animal-calls-genitals.html">rub their genitals</a> against ridges on their bodies to produce mating songs that rival in loudness listening to an orchestra from the front-row seat. Truly an award-winning feat.

  • Best Sound Editing

    This award goes to the animal with the all-around coolest call. <b>Nominees:</b> Barking piranhas, for their species-bending approach to communication; Dolphins <a href="http://www.livescience.com/18074-dolphins-sleep-talk-whale-song.html">sleep-talking in foreign tongues</a>; and the lion, for its grating, effortless roar. <b>And the winner is</b> ... the dolphin. These marine mammals go the extra mile by mimicking the sounds of other species. Recently, a group of captive dolphins in France was caught sleep-talking in the language of whales -- a language they'd only heard played on recordings at their aquatic theme park home. We assume they're getting into Method acting.

  • Best Music

    This award goes to the animal with the most melodious call. <b>Nominees:</b> The Philippine tarsier (we're sure its <a href="http://www.livescience.com/18359-embargoed-world-highest-pitched-primate-calls-bat.html">ultrasonic calls</a> sound pleasant to its own kind); the crooning Emei music frog; and the humpback whale. <b>And the winner is</b> ... the humpback whale. It's a tough call, but the haunting music of humpback whales takes the Animal Academy Award. The whales are amazingly diverse, with different populations <a href="http://www.livescience.com/18279-humpback-whale-songs-distinct.html">singing distinct songs</a>. The songs also <a href="http://www.livescience.com/665-grammar-revealed-love-songs-whales.html">follow grammatical rules</a> to convey information.

  • Best Makeup

    This award goes to the creature that can best alter its appearance to blend in. <b>Nominees</b>: The black-marbled jawfish, for its ability to <a href="http://www.livescience.com/17745-fish-mimics-octopus.html">mimic an octopus</a> that mimics a fish; the land snail <em>Napaeus barquini</em>, for its do-it-yourself application of camouflaging lichen; and the <a href="http://www.livescience.com/12688-psychedelic-cephalopods-swiftly-switch-color-schemes.html">cuttlefish</a>, which can mimic both the color and the texture of its surroundings. <b>And the winner is</b> ... the black-marbled jawfish. We love the multidimensional portrayal of a mimic mimicking a mimic. And whose heart wouldn't be melted by the plucky little underdog jawfish finding a way to venture out of his burrow without fear of predators?

  • Best Costume Design

    This award goes to the flashiest, most colorful animal around. <b>Nominees</b>: The <a href="http://www.livescience.com/17138-poison-frogs-color-evolution.html ">poison dart frog</a>, which has evolved brilliant neon skin to warn predators of its toxicity; the peacock, for reasons both obvious and iridescent; and the harlequin shrimp, for its clownlike colors and extra frills. <b>And the winner is </b>... the harlequin shrimp. These pretty predators are popular for aquarium enthusiasts, but their diet makes keeping them in captivity tricky: The shrimp eat only starfish. And they eat them alive. Sometimes over a period of weeks. Let's move on to the next category, shall we?

  • Best Supporting Actor/Actress

    This award goes to the animal with the weirdest group behavior. <b>Nominees:</b> Guppies, for their Jerry-Springer-worthy "girl fights" over males; <a href="http://www.livescience.com/18326-beetle-sperm-evolution.html">diving beetle sperm</a> (yes, we know, technically not an animal!), for their creepy ability to join together to navigate the female reproductive tract; timber rattlesnakes, for their heretofore unknown snuggly behavior. <b>And the winner is</b> ... snuggly snakes. Rattlesnakes seem like the standoffish sort, but new research suggests that they're actually <a href="http://www.livescience.com/18577-rattlesnakes-social-animals-kin.html">more sociable</a> than expected, clustering with their kin. Rattlesnake family reunion, anyone?

  • Best Actor

    This prize is for the best male mating display. <b>Nominees:</b> The always over-the-top peacock, for his garish feather displays; the hilarious houbara bustard, for their <a href="http://www.livescience.com/15410-sexy-show-offs-burn.html">wild mating runs</a>, which have them flinging a shield of white feathers over their faces and scampering around blindly; and the marvelous <a href="http://www.livescience.com/1480-video-reveals-rare-hummingbird-courtship-display.html">Spatuletail hummingbird</a>, which whirls its long tail in circles to impress the ladies. <b>And the winner is</b> ... the houbara bustard. Tough competition for this one, and the Animal Academy doesn't usually reward comedy, but the houbara bustard gives it his all for this win. Plus chest features are totally in this year.

  • Best Actress

    Though females aren't usually as flashy as males in the wild, this award goes to the female animal that puts on the best mating display. <b>Nominees:</b> Female butterflies, which, if raised in cool temperatures, take it upon themselves to <a href="http://www.livescience.com/9216-cool-weather-heats-female-butterfly-quest-sex.html">pursue males</a> for mates; Wilson's Phalaropes, which switch the usual sex roles and put on flashy courtship displays to snag guys; and the bonobo, for whom sex is an anything-goes group activity. <b>And the winner is</b> ... the Wilson's Pharlarope. Females in this species of shorebird show up at breeding grounds first and puff up their feathers to lure in mates. Once they snag a guy, they defend him zealously, protecting a territory around the nest where he cares for their babies.

  • Best Picture

    <b>Nominees</b>: Zombie ants, who capitalize on zombie-mania when attacked by a <a href="http://www.livescience.com/14064-zombie-ant-fungus-parasite.html">mind-controlling fungus</a>; the glowing millipedes of the genus Mytoxia, who <a href="http://www.livescience.com/16221-glowing-millipedes-toxic-warning.html ">sweat cyanide</a> to ward off predators; and the <a href="http://www.livescience.com/16564-cyclops-shark-cryptozoology.html">Cyclops shark</a>, a malformed dusky fetus whose look mixes grotesque and cute in equal measure. <b>And the winner is</b> ... the Cyclops shark. Millipedes and ants are forever, but this weird fetus is one-of-a-kind, or at least very rare. Considering that the fetal shark is very unlikely to have survived outside the womb, the least we can do is offer it a nice posthumous statuette -- and, of course, the <a href="http://www.livescience.com/16582-cyclops-shark-pictures.html ">obligatory Academy Award memorial reel</a>.