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Dogs can learn to recognize smiles, study finds

March 2, 2011
Special to World Science staff

Dogs can learn to tell apart smiles from blank ex­pres­sions in pho­tographs of peo­ple, a study has found. But wheth­er they rec­og­nize and re­spond to smiles in real life is open to ques­tion, ac­cord­ing to the re­search­ers.

“Although it re­mains un­clear wheth­er dogs have hu­man-like sys­tems for vis­u­al pro­cess­ing of hu­man fa­cial ex­pres­sions, the abil­ity to learn to dis­crim­i­nate hu­man fa­cial ex­pres­sions may have helped dogs adapt to hu­man so­ci­ety,” the sci­en­tists, with Az­abu Uni­vers­ity in Ja­pan, wrote in a re­port on the find­ings.

They put five pet dogs through a train­ing course de­signed to teach them to re­act dif­fer­ently to smil­ing and un­smil­ing pho­tos of their own­er. Four oth­er dogs that in­i­tially were in the study were re­jected from the train­ing be­cause their eyes kept wan­der­ing from the pho­tos.

The trained dogs, all lab­ra­dor re­triev­ers or poo­dles, were lat­er tested with new pho­tos. All five “were able, sig­nif­i­cantly more of­ten than ex­pected by chance, to dis­crim­i­nate their own­ers’ smil­ing faces from their blank faces,” wrote the re­search­ers, Miho Na­ga­sawa and col­leagues. “When shown pho­tographs of un­fa­mil­iar per­sons, they were al­so able to sig­nif­i­cantly more of­ten dis­crim­i­nate smil­ing faces from blank faces,” but only if the pic­tured peo­ple were of the same gen­der as the own­er.

“These re­sults sug­gest that dogs can learn to dis­crim­i­nate be­tween smil­ing and blank hu­man faces con­di­tion­al­ly.” Which fa­cial fea­tures and changes dogs use to rec­og­nize the smiles is un­known; they might have based their choices on the ap­pear­ance of teeth, Na­ga­sawa and col­leagues not­ed.

“A­mong hu­mans, the abil­ity to ac­cu­rately rec­og­nize oth­er peo­ple’s ex­pres­sions and judge their emo­tions is a vi­tal so­cial skill. This study has shown that dogs that live closely with hu­mans are al­so able to rec­og­nize pos­i­tive fa­cial ex­pres­sions, in­di­cat­ing that these dogs have ac­quired the so­cial skills help­ful to sur­vive,” they wrote.

“In re­cent years, sci­en­tists have be­gun to fo­cus on so­cial vis­u­al cog­ni­tive abil­i­ties in dogs’ in­ter­ac­tions with hu­mans,” they added. “For ex­am­ple, if a hu­man throws a ball for a dog to fetch and then turns his back, the dog al­most al­ways brings the ball back around the hu­man’s body in or­der to drop it in front of his face…. Dogs can al­so un­der­stand the rela­t­ion­ship be­tween the di­rec­tion in which hu­mans are fac­ing or gaz­ing and their at­ten­tion­al state.”

Past re­search, they added, has al­so shown that dogs re­spond dif­fer­ently to pho­tos of their own­ers’ faces and those of oth­er peo­ple, and gen­er­ate an “in­ter­nal rep­re­senta­t­ion of the own­er’s face when they hear the own­er call­ing them.”

The new study ap­pears in the Feb. 26 ad­vance on­line is­sue of the re­search jour­nal An­i­mal Cog­ni­tion.


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Dogs can learn to tell apart smiles from blank expressions in photographs of people, a study has found. But whether they recognize and respond to smiles in real life is open to question, according to the researchers. “Although it remains unclear whether dogs have human-like systems for visual processing of human facial expressions, the ability to learn to discriminate human facial expressions may have helped dogs adapt to human society,” the scientists, with Azabu University in Japan, wrote in a report on the findings. They put five pet dogs through a training course designed to teach them to react differently to smiling and unsmiling photos of their owner. Four other dogs that initially were in the study were rejected from the training because their eyes kept wandering from the photos. The trained dogs, all labrador retrievers or poodles, were later tested with new photos. All five “were able, significantly more often than expected by chance, to discriminate their owners’ smiling faces from their blank faces,” wrote the researchers, Miho Nagasawa and colleagues. “When shown photographs of unfamiliar persons, they were also able to significantly more often discriminate smiling faces from blank faces,” but only if the pictured people were of the same gender as the owner. “These results suggest that dogs can learn to discriminate between smiling and blank human faces conditionally.” Which facial features and changes dogs use to recognize the smiles is unknown; they might have based their choices on the appearance of teeth, Nagasawa and colleagues noted. “Among humans, the ability to accurately recognize other people’s expressions and judge their emotions is a vital social skill. This study has shown that dogs that live closely with humans are also able to recognize positive facial expressions, indicating that these dogs have acquired the social skills helpful to survive,” they wrote. “In recent years, scientists have begun to focus on social visual cognitive abilities in dogs’ interactions with humans,” they added. “For example, if a human throws a ball for a dog to fetch and then turns his back, the dog almost always brings the ball back around the human’s body in order to drop it in front of his face…. Dogs can also understand the relationship between the direction in which humans are facing or gazing and their attentional state.” Past research they added, has also shown that dogs respond differently to photos of their owners’ faces and those of other people, and generate an “internal representation of the owner’s face when they hear the owner calling them.” The new study appears in the Feb. 26 advance online issue of the research journal Animal Cognition.