Racial disparities have hindered police-community relations. Now research shows that they originate in a surprising place: an officer’s tone of voice.

A new University of Michigan study showed that officers communicate in a friendlier, more respectful and less tense manner to white men during routine traffic stops, but in a less positive tone to Black drivers. These interactions, in turn, shape people’s perceptions of and trust in law enforcement.

In studies conducted in laboratory and community settings, respondents listened to the voice content from officer-worn body cameras. Without knowing the race of the male drivers or hearing their voices, they answered questions about the short clips of the officers’ conversation.

The researchers sought to move beyond what little is known about interpersonal aspects of officer behavior when police records are scrutinized. Body cameras, however, can capture the nuances of conversations law enforcement have with the public.

Nicholas Camp, U-M assistant professor of organizational studies and study’s lead author, and his colleagues revealed racial disparities in officers’ language in a previous study. This led them to question whether gaps in officer respect emerged not just in what officers say, but how they say it.

“Racial disparities in cues as subtle as an officer’s tone of voice can shape citizens’ trust in the police and alter their interpretation of subsequent encounters,” Camp said.

In the first study, which included three separate analyses, respondents listened to a group of 450 recordings of more than 100 officers communicating to Black or white males during routine traffic stops. The drivers’ speech was removed from the audio, leaving nearly 12 seconds of the officers’ words. As a result, respondents could not tell the drivers’ race when the interactions occurred.

Respondents rated if the officer sounded friendly, at ease and respectful to the driver, or took a cold tone. They also assessed their trust and personal experience with the police. Study participants perceived the officer’s tone of voice toward white drivers as being more positive than the tone toward Black drivers: more respectful, more at ease and more friendly.

What do these disparities mean for police-community trust? In a follow-up study, Camp and colleagues asked nearly 250 customers at a DMV office to listen to 20 audio clips. However, half of the participants listened to 20 clips of officers speaking with Black men, while the other respondents listened to officers speaking to white men.

Participants who listened to officers conversing with Black drivers said they would be less trusting and supportive of the police department, compared to those who listened to the police speaking to white drivers.

Overall, the study shows that officer communication matters in building—or eroding—police-community trust. It also illustrates how body camera footage can reveal patterns in large numbers of police encounters.

Camp and his colleagues hope to measure the impact of policy change and training programs. They are currently working with law enforcement agencies to improve these common but consequential encounters.

The findings appear in the Journal of Personality and Social Psychology: Attitudes and Social Cognition.

The study’s authors include Rob Voigt, assistant professor of linguistics at Northwestern University, and Stanford University’s Dan Jurafsky, professor of linguistics and computer science, and Jennifer Eberhardt, professor of psychology.

More information:

• Study (PDF): The Thin Blue Waveform: Racial Disparities in Officer Prosody Undermine Institutional Trust in the Police