To solve the mystery behind what enables people to properly relate owners to their dogs, Sadahiko Nakajima, a psychologist from Kwansei Gakuin University in Japan, conducted a study that involved 502 Japanese undergrads. This was not Nakajima's first attempt at it. In the previous research, he and his colleagues had shown that the participants could match photos of owners and their dogs by facial look alone.

In the latest study, all the participants were provided with two test sheets and every sheet had about 20 photo sets of dog-human pairs, showing their faces side-by-side.

In order to remove irrelevant factors, the photos selected for the task were of basic color headshots cropped at the shoulders and showed alongside a plain white background. These photos were taken earlier at dog lovers field festival and the owners were asked to look straight at the camera and smile. Dogs' photos were also taken in the same manner. Then, photos were randomly allotted to those two test sheets.

The judge's work was simple as they had to select the set of dog-owner pairs that physically looked like each other. Then, participants were allotted with different masking conditions. The difference in these conditions was the way the photos were presented to the judges on the two sheets.

There were few condition as well, comprising no-mask, in which full faces of humans and dogs were visible to the participant; eye-mask, in which eyes of human were covered with black rectangular bars; mouth with mask, in which the human mouths were covered and dog-eye mask, wherein the dogs' eyes were covered.

About 49 of the 61 judges selected the set of images showing the real-life pairs. Those who saw the same photo sets but with the owners' mouths covered were less impressive. By contrast, by covering the eyes either of the humans or of the dogs made the judge's performance falls statistically. Findings of the study have been published in the journal Anthrozoös.

People are amazingly talented at knowing that which pooch goes with which person on the basis of their facial appearance. So, in the recent study, Nakajima teased apart the many possibilities to find out which facial features people use to make their bizarrely correct decisions.

The importance of this study is its capability to tell that which physical sign people don't use to properly match dogs with their human owners.