Statistics reveal that black Americans are more than twice as likely as white Americans to be unarmed when killed during encounters with police. This is one of the most dramatic examples of how implicit stereotypes, usually consciously disavowed, influence behaviour in highly charged contexts.

In addition, psychological research shows that university students and police officers are more likely to misidentify harmless objects as weapons when they are associated with a black person. Consequently, in laboratory simulations, they are more likely to ‘shoot’ unarmed black people. Although these studies highlight factors that may influence this biased behaviour, the precise underlying physiological mechanism remains largely unknown.

A new study, led by Professor Manos Tsakiris and Dr Ruben Azevedo from Royal Holloway, University of London and The Warburg Institute at the University of London’s School of Advanced Study, has now examined how people misperceive images of potential threat shown to them during or between heartbeats. The resulting report, ‘Cardiac afferent activity modulates the expression of racial stereotypes’, has been published in open access journal, Nature Communications.

Cardiac afferent activity modulates the expression of racial stereotypes 

This work extends earlier research conducted by the report’s co-authors Dr Sarah Garfinkel and Professor Hugo D Critchley, who are from Brighton and Sussex Medical School (BSMS). Their findings show that signals from individual heartbeats, telling the brain about the state of bodily arousal, can increase a person’s sensitivity to threat and fear at the expense of attention to other information.

Dr Azevedo and colleagues conducted a set of experiments using pictures depicting black or white individuals holding guns or mobile phones. Pictures were presented briefly during heartbeats (coinciding with heartbeat arousal signals) or between heartbeats (no heart arousal signals).

The volunteer participants were asked to judge whether the object was a gun or a phone. As in earlier research, those taking part were more likely to misidentify innocent objects as guns when they are carried by black people.  It was found that when the image was flashed at them during the heartbeat, as opposed to between heartbeats, they were approximately 10 per cent more likely to perceive the object as a gun when it was held by a Black person.

Remarkably, the team found that these identification errors predominantly occurred during the timing of bodily arousal signals. ‘The misidentification of tools as weapons when associated with black individuals was increased when the stimuli were presented during a heartbeat, but not between heartbeats,’ explains Professor Tsakiris. ‘This suggests that the combination of the firing of signals from the heart to the brain, along with concurrent presentation of threat, increases the chances that even a non-threat will be perceived as threatening.’

‘While our study specifically looked at the bias against black individuals, that so often in real life has tragic consequences, it is entirely possible that this could apply in other situations,’ says Dr Azevedo. ‘When physically and emotionally aroused – as in a tense situation – faster stronger heartbeats may lead to greater likelihood of perceiving threat where there is none and making an error in judgment.’

Commenting on the study’s usefulness for questions around police shootings of unarmed black people, Dr Sarah Garfinkel, a research fellow in emotion and neuroscience, says   ‘This research has important implications for understanding racially based behaviour.’ Professor Hugo Critchley, her BSMS colleague adds, ‘We can use it to think about potential ways to target this heart-brain communication to reduce the number of tragedies caused by racial bias.’

Cardiac afferent activity modulates the expression of racial stereotypes’, has been published in open access journal, Nature Communications.