There are many subtle ways humans signal and cue one another. In some cases unconscious biases can influence the signals sent, sometimes in the form of negative cues that researchers call “micro-inequities.” Repetitive exposure to these instances can add up over time and drastically affect someone’s feelings of belonging and worth.
Physical cues can also have a significant impact on an individual’s feelings of inclusion and their likelihood to engage in a particular activity. Research shows how individuals see themselves reflected in their surroundings (or the lack thereof) can have physiological and cognitive effects. In this particular study, participants were asked to watch a video of a conference with a male-dominated audience. Researchers tracked significant increases in the stress levels of female viewers, as well as a lower sense of belonging and interest in conference participation than those who watched a video with a more gender-balanced audience. When thinking about building a workforce, conference panels, or event attendee lists Google wants to be cognizant of representation and thoughtful about what unintentional signals might be present and the message that's sending.
A different study showed that physical environment can actually influence an individual's interest in pursuing a certain career path or line of work. In this study, researchers asked undeclared underclassmen about their interest in computer science. They found that the decorations of the room itself where the students participated could influence their stated interest. When the room was adorned with stereotypically “geeky” items (Star Trek posters and video games) women were significantly less likely to express interest in computer science than when the room had more neutral (nature posters and phone books) decorations.
This is not to say that you should create equally unwelcome environments for everyone, but it's important to consider how workplaces might alienate certain groups or send subtle message that only certain types of people are welcome. This didn't mean Google threw out the Legos, Star Wars posters, or Nerf guns. But Google is encouraging employees to be thoughtful about workplace design and decoration.